Review: Welfare Outcomes Of Leg-Hold Trap Use In Victoria
Prepared By Nocturnal Wildlife Research Pty Ltd September 2008
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Welfare outcomes of leg hold trap use part 2
7.0 COMPARISION OF DEVICES
7.1 Welfare outcomes
7.1.1 Steel-jawed leg-hold traps
Toothed, steel-jawed leg-hold traps cause serious injuries, including compound fractures, dislocations and amputations of limbs. Not all animals caught in toothed Lane’s traps sustained injuries that were considered debilitating, but in a comparative assessment of four other devices, they were the only device where animals were found dead in the trap (Fleming et al. 1998). Unpadded traps such as the Victor #3 NM, Victor #3NR, Victor #3 coil springs and Newhouse #4 produce major injuries to coyotes (Phillips 1996b). Of 196 red and grey foxes trapped with #1 to #3 long-spring type traps (#1 ½ being the most common), 26% were believed to have been crippled through self mutilation or escaping with traps attached to limbs. The potential for survival was considered to be low, although survival with the loss of one or two toes is common and these animals have been reported to be re-trapped (Atkeson 1956). Over two years the survival rate of marked and released nutria (Myocastor coypus) previously trapped in leg-hold traps (Victor #11 long spring, Victor #1½ coil spring, Victor #2 long spring or Victor #2 coil spring traps) or cage traps was compared. Released nutria that had been captured in a leg-hold traps experienced a significantly greater mortality rate (74% compared to 53% for those cage trapped). In this study, it was unknown if the type of leg-hold trap used influenced survival (Chapman et al. 1978). Subsequent to capture by steel-jawed ‘Lane’s’ traps, 14% of common wombats were shown to have major injuries and the remaining 86% displayed minor wounds. Wallabies and kangaroos received major wounds on 61% and 83% of occasions, respectively. Major wounding occurred in 65% of foxes, 69% of possums and 84% of birds (Murphy et al. 1990) (Table 11)
7.1.2 Modified steel-jawed leg-hold traps
Modifications were made to # 2 double coil spring traps by removing one spring and padding the jaws with adhesive tape after the sharp edges were filed blunt. Of 86 adult foxes captured, four broke legs and 7/65 cubs broke legs in similarly modified # 1 ½ traps (Sheldon 1949). Based upon a comparison of injuries sustained by grey wolves in toothed or smooth jawed traps with either off-set or fully closing jaws, Van Ballenberghe (1984) observed that #14 toothed traps off-set by 1.8 cm appeared to produce less cuts and major injuries (trap inspection time unstated). Lane’s traps were modified with padding and offsetting the jaws of the trap so that they did not fully close (Harden 1985) and this reduced the injuries produced compared with unpadded Lane’s traps (Fleming et al. 1998). Thompson (1992) used padded Lane’s leg-hold traps (trap inspection time unstated) and 21/205 (10.2%) dingoes died directly as a result of trapping believed to be caused by a combination of exposure, exhaustion and shock. Most trapped dingoes sustained minor cuts or oedema of the trapped leg or foot and their gait appeared normal within days of capture. Although 33/205 (16.1%) were released with more serious injuries such as missing toes, 19/33 of these were believed to suffer from no long lasting ill-effects, while 12/33 exhibited abnormal gait and 2/33 became dissociated from the social group and eventually died. In all, 27.3% of dingoes captured in this manner sustained major injuries and 23/205 (11.2%) died either directly as a result of trapping or in the period afterwards (Table 11).
7.1.3 Padded leg-hold traps
Kreeger et al. (1990) studied the behavioural, physiological, biochemical and pathological response of captive and free ranging red foxes to padded Victor Soft-Catch #3 and unpadded steel-jaw traps. Foxes caught in both types of leg-hold traps developed typical stress responses characterised by elevated heart rate, HPA hormones, CK, AST, LDH and neutrophilia. Foxes spent far les time physically resisting padded traps, and recurrent peaks of struggling were restricted to unpadded traps. Unpadded traps appeared less humane on the basis that, among other indicators, foxes had significantly higher levels of blood cortisol, ALP, AST and gamma-glutamyl trans-peptidase (GGT) and greater limb injury damage scores compared to padded traps.
Earlier designs of the Victor #3 Soft-Catch traps were shown to cause minor foot injuries to coyotes (Olsen et al. 1986, Linhart et al. 1988) and had lower capture success than the unpadded Victor #3 NM trap (Linhart et al. 1986, Linhart et al. 1988, Linscombe et al. 1988, Linhart et al. 1992, Houben et al. 1993, Hubert et al. 1997). Progressive modifications to the trap appear to have overcome earlier problems over a number of generations of development and testing (Skinner et al. 1990, Linhart et al. 1992, Phillips et al. 1992, Phillips et al. 1996a). Soft-Catch traps caused the least visible injury to coyotes and 50% (n=10) had no visible injury while the remainder (n=10) had a swollen foot, small cuts or abrasions. This contrasted with the Victor #3 NM trap that caused moderate to severe injuries in 80% of coyotes and the #4 Newhouse traps that caused moderate to severe injuries in 45% (Phillips et al. 1992). The use of #3 Montgomery music wire springs increased the pressure needed to depress the spring levers from 110 kg in the supplied traps to 154 kg (Houben et al. 1993) and appeared to reduce the mean injury score by 7 – 14 points in coyotes (Houben et al. 1993). In comparison to unpadded trap types (Victor #3 NM longspring, unpadded #4 Newhouse and Sterling MJ600) the Victor Soft-Catch #3 was found to have comparable capture rates and efficacy to the other trap devices under a range of trapping conditions. There was no difference among the four traps for capturing the paw below or across the pads, although the Sterling MJ600 had significantly fewer toe captures (Phillips et al. 1996c) (Table 11).
In a comparison of eight capture devices for coyote by the Denver Wildlife Research Centre (USA), the Victor Soft-Catch #3 modified with four coil springs and increased clamping force (3.6 kg cm2, compared to 2.1 kg cm2 for the standard model) produced less than half the mean injury score and higher capture rate (see Chapter 7.3) (CR = 0.97) compared to a laminated Northwoods #3 trap and was the most successful of all devices compared. While the EZ Grip trap and Belisle foot-snare appeared to produce marginally lower median injury scores, they had lower capture rates (CR = 0.88 and 0.64) respectively) (Andelt et al. 1999) and the WS-T snare produced more injury (Shivik et al. 2005). The # 3 ½ EZ Grip was compared with unpadded Stirling MJ600 and the unpadded Northwoods #3 with rolled steel laminations for the capture of coyotes. Trauma scores were based upon those proposed by Jotham et al. (1994) and the ISO trauma scales (Jotham et al. 1994) and median injury scores for the EZ Grip traps were significantly lower than for the other devices. Frame and Meier (2007) found that the EZ Grip trap cased no injury in 74% and 77% of adult and juvenile wolves. Using Victor Soft-Catch #2 and #3 traps, 61% of red foxes were found to have no injury (Englund 1982) (Table 11).
Australian studies that compared a range of devices designed to capture wild dogs and foxes revealed that Victor Soft-Catch traps seriously injured 28.3% of non-target animals and treadle-snares caused serious injuries to 17.1%. The severity of injuries experienced by animals caught in Soft-Catch traps varied between species, with wallabies (mostly Macropus dorsalis and M. rufogriseus) suffering either minor injuries, broken limb bones or dislocations (Fleming et al. 1998). Molsher (2001) used Victor #1 ½ Soft-Catch traps to target feral cats and observed that a non-target fox broke its leg. A cat was captured repeatedly within a relatively short period (10 times in total): its left front leg was swollen and it limped on release. It was found dead two months later. Some foxes caught in 'Victor' traps sustained serious tissue damage and exposure of the metacarpal bone. Meek et al. (1995) found that animals dislocated their legs by entangling themselves and the trap in understorey vegetation while trying to escape, and the shock-absorbing effect of the spring and the swivel were rendered ineffective. Non-target birds were released with the loss of some leg scales after capture in Victor Soft-Catch traps (Meek et al. 1995). An adult fox was euthanased after capture by the scrotum in a Victor Soft-Catch trap (C.A. Marks, unpublished data). Marks et al. (2004) used fourth generation Victor Soft-Catch #3 fitted with a diazepam or placebo TTD to trap dingoes and assessed damage to soft tissue, bone, tendon, and cartilage, consistent with the scoring method described by Onderka et al. (1990). Chipped or broken teeth and total tooth damage scores were similar for the drug TTD and placebo TTD fitted traps. Limb damage was limited in both groups with 13/20 and 16/19 dingo limbs having no visible injury in the placebo and drug groups respectively. Compound fractures and bone damage was limited to a single case of a bone chip on a digit. Superficial damage was generally limited to small cutaneous lacerations and subcutaneous haemorrhage however there was no significant difference in the median limb damage scores for both groups (Marks et al. 2004). Research into the injury sustained by brushtail possums in New Zealand using Lane’s-Ace and padded and unpadded Victor #1 and #1½ traps indicated that serious injuries were caused by traps without padding modifications (Warburton et al. 2004) (Table 11). Recent authors have encouraged further research with padded leg-hold traps as they appear to minimise injuries more than other models or modifications (Hubert et al. 1997) and are the thought to be a significant advance in preventing capture trauma (Phillips 1996).
Pressure necrosis and ischemia may arise from the use of traps or leg-hold snares that restrict blood flow to tissues for prolonged periods, and this may also be at least partly responsible for the initiation of self-mutilation (see Chapter 6.2.1). Ischemia has been described in wolves captured with leg-hold traps (Frame et al. 2007) but the degree to which this occurs in a range of traps is unknown. Dingoes trapped in Victor Soft-Catch #3 traps with modified springs showed signs of necrotic injury upon recapture and this was hypothesised to be a result of constriction caused by the rubber pads (Byrne and Allen 2008). Foxes housed in a research facility were originally trapped with the Victor Soft-Catch #3 trap and showed indications of mild to moderate oedema after removal from the trap and no other trauma. When held in captivity for approximately one week, some were found to develop tissue necrosis and erosions that caused the exposure of tendons (Figure 9d and 9e) (C.A. Marks and F. Busana, unpublished data). The incidence of this trauma in non-target species is not known, nor is the welfare implications of such injury in target species, as most are either euthanased or released before visible pathology develops. Self-mutilation of feet was observed in 2/10 coyotes trapped in Victor Soft-Catch traps that were modified for 40% greater spring tension and a 15 cm chain that restricted activity and movement (Houben et al. 1993). It was suggested that this may have been due to the Soft-Catch trap being more capable of numbing the coyote’s foot (Houben et al. 1993), however the small sample (n=10) of animals taken with the alternative trap (modified Northwoods #3 coil spring) precludes any firm conclusions.
7.1.4 Laminated leg-hold traps
The #3 Northwoods offset jawed, coil-springed traps (Glen Sterling: Faith, South Dakota) were modified with 6.35 mm lamination strips and the average pressure required to depress the jaws was 198 kg. Coyotes captured in unpadded Victor #3 coil spring traps and Victor #3 long-spring traps had an incidence of injury 5-7.5 times greater than those captured in the modified Northwoods traps (Houben et al. 1993). The combination of doubling the width of the jaw area and offsetting jaws, strong springs and improved swivelling system were believed to be responsible for this, however there was no significant reduction in injury scores when compared to the Victor Soft-Catch trap, although these data were based upon small samples (n=10) (Houben et al. 1993). Injuries to coyotes using Northwoods #3 traps modified with unpadded, offset, wide-laminated jaws (12.8 mm) and centre mounted anchor chains where significantly higher than for padded #3 ½ EZ Grip long-spring traps (Phillips et al. 1996b).
Trap related injuries in red foxes using # 1 ½ coil spring traps were less serious when jaws were offset and laminated (Kern et al. 1994, in Hubert et al. 1997). However, no statistically significant reduction in injury was detected when larger Bridger #3 traps were modified with similar lamination (total width = 9.5 mm) and offset, although some reduction in mean injury scores (28% reduction in whole body injury) was implied (Hubert et al. 1997). In contrast, between 48-85% reductions in injury have been documented for coyote capture using the #3 Victor Soft-Catch trap (Olsen et al. 1986, Olsen et al. 1988, Onderka et al. 1990, Hubert et al. 1997) (Table 11).
7.1.5 Leg-hold snares
Iossa et al. (2007) reviewed the welfare performance of leg-hold snares and found that they are generally associated with less mortality than leg-hold traps. Approximately 51% of foxes captured with foot-snares (Nordic Sports AB: Kellefteå: Sweden) were found to have dental injury compared to 94% and 75% captured in Victor long-spring traps (Englund 1982). Cable restraints used in trials with the Belisle and WS-T snare caused swelling and lacerations as well as fractured and chipped teeth, probably from chewing the cable. When compared to the Collarum neck snare, both produced far greater injury scores (Shivik et al. 2000). The ‘Rose Leg Cuff’ uses a Kevlar band that encloses the trapped leg and has been used with success to restrain foxes and badgers in the UK, where the only trauma reported was temporary swelling of the trapped paw (Kirkwood 2005). In Australia, visible trauma associated with the treadle-snare was significantly reduced compared to large (Lane’s) steel-jawed traps (Stevens and Brown 1987, Murphy et al. 1990, Fleming et al. 1998) and was believed to be similar to trauma caused by Victor Soft-Catch #3 traps (Meek et al. 1995). Meek et al. (1995) indicated that the most serious injuries sustained by foxes caught in treadle-snares were lacerations caused by the edges of the snare-locking bracket rubbing on the skin. Bubella et al. (1998) captured 71 red foxes with treadle-snares and three suffered broken legs and were shot. Most individuals showed swelling of the lower foreleg due to loss of circulation and skin abrasions, depending on the length of time spent in the trap. Forty red foxes that were radio-tracked and observed for up to two years following trapping showed no apparent long-term adverse effects such as visible deformation of limbs or limping. The nine individuals that were recaptured showed no sign of having been trapped previously as no scarring or thickening of the limb was seen. Fleming et al. (1998) indicated that approximately 55% of dogs, foxes and cats received no injury as a consequence of capture in the treadle-snare (Table 11).
The behaviour of different species when snared will greatly influence the amount of trauma sustained. For instance, after capture with a snare based upon the Aldridge snare throwing arm, lions (Panthera leo) appear to resist little and had no broken skin or injury (Frank et al. 2003). Snares used to capture black bears can cause swelling and lacerations around the restrained area and constant tugging can cause fractures, muscle, tendon, nerve and joint injury (Lemieux et al. 2006). In a study by Powell (2005), black bears were captured with Aldridge-type foot-snares and capture injury and blood biochemistry was compared with bears captured in their dens and those recovered with immobilising dart collars. Snaring resulted in less than 70% of the population incurring damages consistent with a score of ≤ 50 points according to the scoring system used by Powell and Proulx (2003). Blood biochemistry parameters corresponding to higher levels of exertion in snared adult bears in comparison with those recovered by dart collars and included elevated Gl, ALB, AP, ALT, LDH and CK. Dehydration was indicated by changes in Gl, ALB, ALB:globulin ratio and TP. Elevated CK and LDH were indicative of high levels of exertion during snaring relative to other recovery techniques (Powell 2005). Spring activated leg-hold snares (Margo Supplies: Alberta, Canada) used to capture grizzly bears caused elevated CK, AST and ALT which was suggestive of muscle damage following capture, related to tightening of the cable on the forelimb and excessive strain on the muscles and joints. A higher N:L ratio was typical of a stress leukogram as well as increased concentrations of Na and Cl -that indicated dehydration as a result of being deprived of water for 2-23 hours aggravated by intense activity (Cattet et al. 2003). Elevation of muscle enzymes has also been reported for black bears (Ursus americanus) and polar bears (Ursus maritimus) captured by leg-hold snares (Lee et al. 1977, Schroeder 1987, Huber et al. 1997).
Compared to other recovery methods (cage traps, netting and Victor Soft-Catch #3 traps), foxes captured in treadle-snares had significantly higher mean ALB, CK, RCC, N:L ratio, Na, TP and white cell counts (WCC). Treadle-snares were also associated with higher Cl -, Hb and packed cell volume (PCV) than cage trapping and netting. These were indicators of greater muscle damage, exertion and dehydration (Marks, in review, Appendix 1) similar to that reported in snared black bears (Powell 2005) and grizzly bears (Cattet et al. 2003). Treadle-snares were tethered to a solid fixture by a length of snare cable and chain that was 2 m in length, in contrast to 0.5 – 0.75 m chains that were used to anchor the Victor Soft-Catch traps (Marks, in review, Appendix 1). Foxes have the ability to run or leap to the end of the snare tether where they are brought to a sudden stop, while their coordinated movement appears to be impaired when caught in a leg-hold trap (C.A. Marks, personal observations). Longer tethers and an ability to develop large momentum before being pulled to a sudden stop may be associated with greater activity and muscle damage (Chapter 8.3). The apparently greater metallic noise associated with activated treadle-snares (Chapter 6.1.7 and Chapter 8.5) may be an additional stressor that promotes increased activity in comparison to that associated with the Victor Soft-Catch trap.
Limb oedema was an almost universal observation of red foxes that had been recovered by treadle-snares (Figure 6a and 6b) and Victor Soft-Catch traps (Figure 6c and 6d) and this was photo-documented in trapped foxes received by the Victorian Institute of Animal Science (Frankston, Victoria, Australia) and housed in the institute’s fox facility (C.A. Marks and F. Busana, unpublished data). Some foxes captured with treadle-snares were found to have trauma typical of deep, compressive wounds, and lacerations caused by the locking bracket and cable. Oedematous swelling, which appeared to worsen within the first day after capture, was consistent with observations of ischemia and reperfusion injury (Chapter 6.2.1). In some animals, skin and muscle necrosis became apparent within 3-5 days of trapping and extensive erosion of the injury site was exacerbated by foxes licking and debriding the wound (F. Busana, personal observations). Tendon and bone was exposed and muscle tissue had a purple to crimson appearance typical of necrotic tissue (Figure 9a-9c). The progression of this pathology was believed to be consistent with that described for ischemic conditions leading to outcomes of long-term or permanent debilitation (Chapter 6.2.1). The time period that the foxes had been captive in the snare prior to recovery was unclear.
7.1.6 Neck snares
When set correctly, serious injury was reported to be relatively uncommon from non-lethal neck snares used in the UK, although mortality may be higher than for foot-snares due to their frequent misuse (Kirkwood 2005, Iossa et al. 2007). The welfare outcomes from neck snaring of foxes in the UK can be variable as the methods used to manufacture, set and monitor neck snares differ and the proportion of non-target species captured can range from 21-69% (Kirkwood 2005). The Collarum neck snare appears to be more target-specific than many leg-hold traps and snares as it uses a baited lure to trigger it and it is set above ground level, which may allow more selectivity for capturing coyotes (Shivik et al. 2000). The Collarum appears to causes few cases of major injury, with the most conspicuous trauma being tooth damage, probably from chewing on the cable (Shivik et al. 2000). While cases of deaths have been recorded due to the failure of the system to trigger correctly, this is relatively rare (Shivik et al. 2005). The ISO injury scores for two versions of the Collarum neck snare (2.5 and 5.4) were far lower than for the WS-T (12.3) and Belisle snare (22.5) (Shivik et al. 2000). When the Collarum was compared to the WS-T and Victor Soft-Catch in another study, damage scores were 2.5, 30.7 and 21.7 (scoring system after Phillips et al. 1996) respectively (Shivik et al. 2005). Neck snares equipped with diazepam tabs reduced the number of coyotes with oral lacerations and facial injuries (Pruss et al. 2002) and the potential to incorporate this approach with the Collarum snare may reduce injuries further (Table 11). Lethal wire neck snares were assessed in the field and of 65 coyotes recovered, only 59% were captured by the neck. Of the remainder, 20% were captured by the flank, 11% by the front legs and neck and 10% by the foot. Of these, 48% were found to be alive by morning although a proportion were moribund (Guthery et al. 1978). Using power neck snares, foxes could be rendered unconscious in a minimum of six minutes but the device also tended to capture some individuals around the body or head (Proulx et al. 1990).
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Figure 9. Appearance of lower limb of foxes restrained by the treadle snare (a,b,c) and Victor Soft-Catch #3 trap (d,e) 6-11 days after capture showing various degrees of tissue necrosis and erosion exposing tendon and bone. Upon capture these foxes were all observed with oedematous swelling, but no other obvious trauma. Capture duration is unknown.
Table 11. Trap and snare type used to capture canids (wild dogs, dingo, wolf, coyote and red fox) and non-target species and the percentage with no injury (NIL), minor injury (MIN), major injury (MAJ) and those that were dead upon recovery (DEAD). (Minor injury = swelling, cutaneous, tendon or ligament lacerations corresponding to up to 20 points of trauma scale proposed by Tullar 1984, Olsen 1988, Onderka et al. 1990, Hubert et al. 1996. Major injury = trauma > 20 points corresponding to degrees of joint luxation, fractures or amputation. Minor injury corresponds to class I and II (Van Ballenberghe 1984, Kuehn et al. 1986, Frame and Meier 2007), < class III with class I corresponding to no injury (Fleming et al. 1998), class I, II and III (Stevens and Brown). Cause of death is inclusive of trauma from trap related injury or predation of captive animal.
| % | % | % | % | ||||
|---|---|---|---|---|---|---|---|
| TRAP AND SNARE TYPE | TARGET | N | NIL | MIN | MAJ | DEAD | AUTHORITY |
| Belisle foot snare | Coyote | 16 | 1 | 0 | Shivik et al. 2000 | ||
| Bridger #3 | Coyote | 19 | - | 21 | 79 | - | Hubert et al. 19971 |
| Bridger #3 (laminated-offset) | Coyote | 29 | - | 28 | 72 | - | Hubert et al. 19971 |
| Collarum neck snare (1998 | |||||||
| version) | Coyote | 16 | 0 | 0 | Shivik et al. 2000 | ||
| Collarum neck snare (1999 | |||||||
| version) | Coyote | 24 | 4 | 1 | Shivik et al. 2000 | ||
| Collarum neck snare | Coyote | 13 | 30 | 62 | 0 | 7 | Shivik et al. 2005 |
| EZ Grip #7 | Wolf (adult) | 70 | 74.3 | 17.1 | 8.6 | 0.0 | Frame et al. 2007 |
| EZ Grip #7 | Wolf (juv) | 26 | 76.9 | 11.5 | 11.5 | 0.0 | Frame et al. 2007 |
| Lane’s (large steel-jawed) | Dog, fox and cat | 73 | 5.5 | 63.0 | 26.0 | 5.5 | Fleming et al. 1998 |
| Lane’s (large steel-jawed) | Dog, fox and cat | 123 | 3.3 | 65.9 | 27.6 | 3.3 | Stevens et al. 1987 |
| Lane’s (large steel-jawed) | Non-target | 56 | 8.9 | 32.1 | 46.4 | 12.5 | Stevens et al. 1987 |
| Lane’s (large steel-jawed) | All | 179 | 5.0 | 55.3 | 33.5 | 6.1 | Stevens et al. 1987 |
| Lane’s (large steel-jawed) | Fox | 268 | - | 35.4 | 64.6 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Rabbit | 63 | - | 19 | 81 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Cat | 114 | - | 54.4 | 45.6 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Wombat | 88 | - | 86 | 14 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Possum | 72 | - | 31 | 69 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Kangaroo | 36 | - | 17 | 83 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Wallaby | 153 | - | 38.6 | 61.4 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Bird | 25 | - | 16 | 84 | - | Murphy et al. 1990 |
| Lane’s (large steel-jawed) | Dingo | 205 | 0? | - | 16.1? | 10.2 | TDomson 1992 |
| Lane’s (padded) | Dog, fox and cat | 313 | 33.6 | 50.5 | 15.9 | 0.0 | Fleming et al. 1998 |
| Lane’s-Ace | Brushtail possum | 78 | - | 71 | 30 | - | Warburton 19921 |
| LPC #4 | Wolf (adult) | 38 | 13.2 | 31.6 | 55.3 | 0.0 | Sahr et al. 2000 |
| LPC #4 | Wolf (juv) | 47 | 44.7 | 48.9 | 6.4 | 0.0 | Sahr et al. 2000 |
| Newhouse #14 | Wolf (adult) | 91 | 5.5 | 61.5 | 33.0 | 0.0 | Kuehn et al. 1986 |
| Newhouse #14 | Wolf (juv) | 38 | 21.1 | 63.2 | 15.8 | 0.0 | Kuehn et al. 1986 |
| Newhouse #14 | Wolf (adult) | 21 | 4.8 | 95.2 | 0.0 | 0.0 | Kuehn et al. 1986 |
| Newhouse #14 | Wolf (juv) | 19 | 0.0 | 100.0 | 0.0 | 0.0 | Kuehn et al. 1986 |
| Newhouse #4 | Wolf (adult) | 182 | 7.1 | 52.2 | 41.2 | 0.0 | Kuehn et al. 1986 |
| Newhouse #4 | Wolf (juv) | 87 | 36.8 | 46.0 | 17.2 | 0.0 | Kuehn et al. 1986 |
| Newhouse #4 | Wolf (adult) | 81 | 9.9 | 51.9 | 38.3 | 0.0 | Kuehn et al. 1986 |
| Newhouse #4 | Wolf (juv) | 35 | 31.4 | 40.0 | 28.6 | 0.0 | Kuehn et al. 1986 |
| Nordic sport foot-snare | Red fox | 115 | 83 | 15 | 3 | Englund 1982 | |
| SmooTD steel-jawed | Dog, fox and cat | 20 | 40.0 | 50.0 | 10.0 | 0.0 | Fleming et al. 1998 |
| Steel-jawed (various) | Wolves | 106 | 44 | Van Ballenberghe 1984 | |||
| Tomahawk snare | Coyote | 7 | 14 | 43 | 29 | 14 | Shivik et al. 2005 |
| Treadle-snare | Dog, fox and cat | 80 | 33.8 | 60.0 | 5.0 | 1.3 | Stevens et al. 1987 |
| Treadle-snare | Non-target | 32 | 43.8 | 40.6 | 12.5 | 3.1 | Stevens et al. 1987 |
| Treadle-snare | All | 112 | 36.6 | 54.5 | 7.1 | 1.8 | Stevens et al. 1987 |
| Treadle-snare | Dog, fox and cat | 117 | 54.7 | 41.0 | 4.3 | 0.0 | Fleming et al. 1998 |
| Treadle-snare | Fox | 71 | - | - | 4.2 | - | Bubela et al. 1998 |
| Treadle-snare | Fox | 523 | - | 81.3 | 18.7 | - | Murphy et al. 1990 |
| Treadle-snare | Rabbit | 14 | - | 79 | 21 | - | Murphy et al. 1990 |
| Treadle-snare | Cat | 126 | - | 93.7 | 6.3 | - | Murphy et al. 1990 |
| Treadle-snare | Wombat | 483 | - | 91.5 | 8.5 | - | Murphy et al. 1990 |
| Treadle-snare | Possum | 79 | - | 73 | 27 | - | Murphy et al. 1990 |
1Indicates scoring category may have some minor overlap or inconsistency when compressed into current injury category.
Table 11 (cont). Trap and snare type used to capture canids (wild dogs, dingo, wolf, coyote and red fox) and non-target species and the percentage with no injury (NIL), minor injury (MIN), major injury (MAJ) and those that were dead upon recovery (DEAD). (Minor injury = swelling, cutaneous, tendon or ligament lacerations corresponding to up to 20 points of trauma scale proposed by Tullar 1984, Olsen 1988, Onderka et al. 1990, Hubert et al. 1996. Major injury = trauma > 20 points corresponding to degrees of joint luxation, fractures or amputation. Minor injury corresponds to class I and II (Van Ballenberghe 1984, Kuehn et al. 1986, Frame and Meier 2007), < class III with class I corresponding to no injury (Fleming et al. 1998), class I, II and III (Stevens and Brown). Cause of death is inclusive of trauma from trap related injury or predation of captive animal.
| % | % | % | % | ||||
|---|---|---|---|---|---|---|---|
| TRAP TYPE | TARGET | N | NIL | MIN | MAJ | DEAD | AUTHORITY |
| Treadle-snare | Kangaroo | 64 | - | 50 | 50 | - | Murphy et al. 1990 |
| Treadle-snare | Wallaby | 281 | - | 64.8 | 35.2 | - | Murphy et al. 1990 |
| Treadle-snare | Bird | 23 | - | 39 | 61 | - | Murphy et al. 1990 |
| Victor # 1½ unpadded | Brushtail possum | 74 | - | 81 | 10 | Warburton 19921 | |
| Victor # 1 unpadded | Brushtail possum | 72 | - | 87 | 12 | Warburton 19921 | |
| Victor #2 & #3 LS (coated) | Red fox | 28 | 36 | 21 | 43 | Englund 1982 | |
| Victor #2 and #3 LS | Red fox | 117 | 61 | 9 | 30 | Englund 1982 | |
| Victor Soft-Catch # 1 | Brushtail possum | 63 | - | 99 | - | 2 | Warburton 19921 |
| Victor Soft-Catch # 1½ | Foxes | 48 | - | 62.5 | 37.5 | - | Olsen et al. 1988 |
| Victor Soft-Catch # 1½ | Brushtail possum | 82 | - | 93 | 7 | - | Warburton 19921 |
| Victor Soft-Catch # 1½ | Foxes | 30 | - | 93.3 | 6.7 | - | Olsen et al. 1988 |
| Victor Soft-Catch # 3 | Coyote | 36 | - | 47.2 | 52.8 | - | Olsen et al. 1988 |
| Victor Soft-Catch #3 | Wild dog | 13 | 7.7 | 76.9 | 15.4 | 0.0 | Stevens et al. 1987 |
| Victor Soft-Catch #3 | Wild dog | 170 | 60.0 | 20.6 | 19.4 | 0.0 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Red fox | 75 | 46.7 | 30.7 | 22.6 | 0.0 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Feral cat | 35 | 68.6 | 28.6 | 2.8 | 0.0 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Dog, fox and cat | 280 | 55.7 | 24.3 | 18.2 | 0.0 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Birds | 45 | 10.2 | 28.6 | 46.8 | 14.3 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Lagomorphs | 32 | 25.0 | 21.9 | 28.1 | 21.9 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Macropods | 29 | 3.5 | 17.2 | 62.1 | 17.2 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Sheep | 12 | 91.7 | 0.0 | 0.0 | 8.3 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Possums | 11 | 54.6 | 27.2 | 0.0 | 18.2 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Varanids | 11 | 27.3 | 0.0 | 45.5 | 27.2 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Rufous bettong | 9 | 44.4 | 22.2 | 22.2 | 11.1 | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Dingo | 20 | 65.0 | 30.0 | 5.0 | 0.0 | Marks et al. 2004 |
| Victor Soft-Catch #3 | Coyote | 31 | - | 83.9 | 16.1 | - | Olsen et al. 1988 |
| Victor Soft-Catch #3 | Coyote | 24 | 4 | 88 | 8 | 0 | Shivik et al. 2000 |
| Victor Soft-Catch #3/TTD | Dingo | 19 | 84.2 | 15.8 | 0.0 | 0.0 | Marks et al. 2004 |
| WS-T leg snare | Coyote | 20 | 0 | 0 | Shivik et al. 2000 |
1Indicates scoring category may have some minor overlap or inconsistency when compressed into current injury category.
7.2 Comparative capture rate
Capture rate (CR) is the ability of the trap to catch and hold an animal, which has sprung the trap. Linscombe and Wright (1988) defined CR as the number of animals captured divided by the potential captures. Potential captures include those animals that have escaped, or if known, those that failed to trigger the trap mechanism that were at the trap site. Under Australian conditions, the CR of Victor Soft-Catch traps (CR = 0.75) were shown to be significantly higher than those for the toothed Lane’s traps (CR = 0.54). No significant difference in CR was found between Lane’s traps and treadle-snares for dogs, foxes and feral cats combined (CR = 0.46) (Fleming et al. 1998). The capture rate for the Novak and Freemont snares did not differ in the capture of coyotes, yet was approximately three times less than for leg-hold traps, and Novak snares missed potential captures more frequently (Skinner et al. 1990). In general, the CR of snares appears to be lower for leg-hold traps and the Belisle (CR = 0.64, 0.78), Panda (CR = 0.08) and WS-T snares (CR = 0.66, 0.88) mostly under-perform contemporary Victor Soft-Catch devices. Although earlier versions of the Collarum neck snare appeared to have less efficacy (CR=0.41) (Shivik et al. 2000), later versions may have improved this (CR=0.87) (Shivik et al. 2005). It is notable that earlier studies using the first generations of Victor Soft-Catch #3 traps reported reduced CR (eg. CR = 0.32, 0.66, 0.49, 0.95), yet all studies conducted after 1996 with coyotes indicate improved results (CR = 0.82, 0.97, 0.95, 0.95, 0.91, 1.0). This suggests superior performance to past versions and comparable performance to unpadded leg-hold devices of the same size. It is unlikely that few (if any) of the Australian Victor Soft-Catch #3 trap data used in the study by Fleming et al. (1998) related to fourth generation traps, since this study collated data from the late 1980’s to early 1990s that was in part reported by Stevens and Brown (1987), and predated these trap modifications (Table 12).
Linhart and Dasch (1992) indicated that coyote capture rates for modified (‘fourth generation’) Soft-Catch traps were comparable with the unpadded leg-hold trap models which are favoured by trappers (CR = 0.79). In one study much lower CR has been reported for Victor Soft-Catch traps during wet conditions (Kern 1994, in Andelt et al. 1999) and when light soils are used for trap placement for coyotes (CR = 0.32) and bobcats (CR = 0.66) (Holt and Connor 1992, in Houben et al. 1993) while the Victor # 1.75 q-coiled off-set jawed trap had a superior CR for coyotes (CR = 0.92) and bobcats (CR = 1.0). However, under a range of operational conditions there was no indication of reduced performance from the Victor Soft-Catch trap in operational studies when trappers closely followed setting instructions (Phillips et al. 1996c). The fourth generation of the #3 Victor Soft-Catch that was re-engineered to have a faster closure was found to be equal in its performance to unpadded traps (Skinner and Todd 1990, Linhart and Dasch 1992, Phillips et al. 1992). When compared to the #4 Newhouse (CR = 1) Victor NM long-spring trap (CR = 1), the high capture rate (CR = 0.95) was similarly attributed to users closely following the manufacturer’s setting instructions (Phillips et al. 1992). Coyotes were taken more effectively with M-44 cyanide ejectors than with the Oneida-Victor No 3 and No 4 traps in a trial of various control devices in Texas (Beasom 1974), although other studies found a similar level of success (Windberg et al. 1990).
Table 12. Trap type and target species and capture rate (CR) measured as the number of animals captured / potential captures for target species in each region.
| TRAP AND SNARE TYPE | SPECIES | CR | REGION | AUTHORITY |
|---|---|---|---|---|
| Belisle foot snare | Coyote | 0.78 | rural USA | Shivik et al. 2000 |
| Belisle foot snare | Coyote | 0.64 | rural USA | Andelt et al. 1999 |
| Collarum neck snare | Coyote | 0.87 | rural USA | Shivik et al. 2005 |
| Collarum neck snare | Coyote | 0.41 | rural USA | Shivik et al. 2000 |
| EZ Grip #3 padded | Coyote | 0.88 | rural USA | Andelt et al. 1999 |
| Heimbrock Special | Coyote | 0.94 | rural USA | Andelt et al. 1999 |
| Newhouse #4 | Coyotes | 1 | rural USA | Phillips et al. 1992 |
| Newhouse #4 | Coyote | 0.89 | rural USA | Phillips et al. 1996c |
| Newhouse #4 | Coyote | 0.83 | rural USA | Phillips et al. 1996c |
| Newhouse #4 pan tension | Coyote | 0.87 | rural USA | Phillips et al. 1996a |
| Northwoods #3 laminated | Coyote | 0.95 | rural USA | Andelt et al. 1999 |
| Lane’s padded | Dogs and foxes | 0.83 | rural Australian | Fleming et al. 1998 |
| Panda foot snare | Coyote | 0.083 | rural USA | Shivik et al. 2000 |
| Lane’s toothed | Dogs and foxes | 0.54 | rural Australian | Fleming et al. 1998 |
| Sterling MJ 600 | Coyote | 1 | rural USA | Phillips et al. 1996c |
| Sterling MJ 600 | Coyote | 1 | rural USA | Phillips et al. 1996c |
| Sterling MJ 600 | Coyote | 0.94 | rural USA | Andelt et al. 1999 |
| Treadle-snare | Dogs and foxes | 0.46 | rural Australian | Fleming et al. 1998 |
| Victor #1.75 coiled off-set jaw | Coyotes | 0.92 | rural USA | Houben et al. 1993 |
| Victor #1.75 coiled off-set jaw | Bobcats | 1 | rural USA | Houben et al. 1993 |
| Victor #3 coil spring | Coyote | 0.91 | rural USA | Linhart et al. 1992 |
| Victor #3 NM long-spring | Coyotes | 1 | rural USA | Phillips et al. 1992 |
| Victor #3 NM long-spring | Coyote | 0.95 | rural USA | Phillips et al. 1996c |
| Victor #3 NM long-spring | Coyote | 0.91 | rural USA | Phillips et al. 1996c |
| Victor #3 NM long-spring | Coyote | 0.95 | rural USA | Andelt et al. 1999 |
| Victor #3 NM long-spring pan tension | Coyote | 0.91 | rural USA | Phillips et al. 1996a |
| Victor #3 NR and OS offset | Coyote | 0.73 | rural USA | Linhart et al. 1986 |
| Victor #3 NR padded | Coyote | 0.51 | rural USA | Linhart et al. 1986 |
| Victor 3NM long-spring off-set jaws | Coyote | 0.83 | rural USA | Linhart et al. 1992 |
| Victor Soft-Catch #3 | Dogs and foxes | 0.75 | rural Australian | Fleming et al. 1998 |
| Victor Soft-Catch #3 | Coyotes | 0.32 | rural USA | Houben et al. 1993 |
| Victor Soft-Catch #3 | Bobcats | 0.66 | rural USA | Houben et al. 1993 |
| Victor Soft-Catch #3 | Coyotes | 0.95 | rural USA | Phillips et al. 1992 |
| Victor Soft-Catch #3 | Coyote | 1 | rural USA | Shivik et al. 2005 |
| Victor Soft-Catch #3 | Coyote | 0.95 | rural USA | Phillips et al. 1996c |
| Victor Soft-Catch #3 | Coyote | 0.91 | rural USA | Phillips et al. 1996c |
| Victor Soft-Catch #3 | Coyote | 0.95 | rural USA | Andelt et al. 1999 |
| Victor Soft-Catch #3 | Coyote | 0.49 | rural USA | Linhart et al. 1986 |
| Victor Soft-Catch #3 | Coyote | 0.79 | rural USA | Linhart et al. 1992 |
| Victor Soft-Catch #3 modified | Coyote | 0.97 | rural USA | Andelt et al. 1999 |
| Victor Soft-Catch #3 pan tension | Coyote | 0.818 | rural USA | Phillips et al. 1996a |
| WS-T snare | Coyote | 0.66 | rural USA | Shivik et al. 2000 |
| WS-T snare | Coyote | 0.88 | rural USA | Shivik et al. 2005 |
7.3 Comparative capture efficacy
Capture efficiency (CE) is usually defined as the number of target captures per trap set standardised as captures per 100 or 1000 trap-nights (Boggess 1990). The CE measure is affected by the expertise of the trapper, population density of the target and non-target animals, previous exposure of the targeted population to trapping, the sex and age structure of the targeted population, seasonal and site characteristics, baits and lures used and the pre-baiting period (Novak 1987). Given the difficulty in controlling for these variables, CE is a highly biased measure and comparative assessments between sites using different techniques should be done cautiously (Fleming et al. 1998). Minor variations in trap setting practices may have major implications for CE. For example, coyotes were found to be more susceptible to capture outside or on the edge of their normal range, if they were between 1-2 years old and when olfactory attractants were used to enhance trapping success (Windberg et al. 1990). McIlroy et al. (1986) used modified Oneida leg-hold traps to capture wild dogs in south-eastern Australia and the CE obtained (CE = 1.56) was similar to that obtained for toothed Lane’s traps and treadle-snares but smaller than CEs obtained for padded Lane’s and Soft-Catch traps (Fleming et al. 1998). Data from Newsome et al. (1983) revealed a CE = 0.58 and 1.72 for toothed Lane’s and Oneida traps respectively. Although highly biased, these data imply that padding modifications and use of smaller traps did not reduce capture of dingoes and foxes under Australian conditions.
7.4 Practicality
Meek et al. (1995) reports that the treadle-snare was effective for capturing foxes under ideal conditions but was bulky, prone to malfunctions and difficult to transport. The Freemont foot-snare also requires more time to set and more regular maintenance than leg-hold traps, and a new snare noose is required after each capture (Mowat et al. 1994), as is the case with the treadle-snare (Meek et al. 1995). Treadle-snares were used to capture 40 individual foxes in Kosciusko National Park and of 136 snares that were sprung, 71 foxes were captured overall (ie. some more than once). Approximately 50% of sprung snares were thought to be related to missed foxes and associated with the difficulty in reliably setting treadle-snares (Bubela et al. 1998). Treadle-snares were used to capture feral cats but in comparison to Victor Soft-Catch traps they were considered expensive, bulky to transport and difficult and time consuming to set (Short et al. 2002).
7.5 Discussion and Conclusions
Padding of trap jaws has been attempted with cloth, plastic or rubber tubing in a number of Australian studies, however no comprehensive assessment of the welfare benefits from this approach can be found. Such modifications probably result in less injury than produced by unmodified devices, yet are unlikely to produce outcomes comparable to commercially available devices that have undergone progressive testing and modification. Devices that have been altered without regard for a stated specification or standard do not permit comparative welfare benefits to be known. A large range of modifications have been made to existing leg-hold trap devices in an attempt to meet injury threshold limits in North America.
There is no compelling evidence to suggest that trap lamination delivers welfare outcomes superior or comparable to those associated with commercially available padded leg-hold traps. Increasing the spring energies and closing velocity of padded traps reduces the number of captures at the extreme ends of the paw that are often implicated in higher rates of injury. As this modification also increases the impact force of the jaws upon capture, the use of materials such as rubberised padding may be necessary to dissipate forces that could otherwise produce acute trauma upon trap closure. There is some data that suggests that this may enhance ischemia, however there is no clear indication as yet that this is significantly greater than for other devices that have similar closing and clamping forces. It is difficult to compare the potential for different traps to cause ischemic injury without reference to their relative closure speeds, clamping forces and jaw characteristics, and the outcomes that these imply. As prolonged ischemia may produce necrotic injury only after many days, the most significant potential welfare impact could be for non-target animals that are released from traps.
The Victor Soft-Catch #3 trap has been extensively field tested in North America and has received some assessment in Australia. The device has undergone at least four ‘generations’ of modification and while earlier versions of the trap were found to be less efficient and reliable than unpadded traps, current versions appear to be at least equivalent in performance. Studies in New Zealand have shown that smaller versions of the Victor Soft-Catch trap produce comparatively better welfare outcomes for brushtail possums which are an important non-target species in south-eastern Australia. The Victor Soft-Catch devices (and possibly the EZ Grip traps that are the subject of much fewer published studies) probably differ from other leg-hold traps in that they are new designs conceived for reducing trap trauma, rather than developed through adaptation of existing devices.
It has been noted that in general, leg-hold snares appear to produce far less trauma than a wide range of leg-hold traps (Iossa et al. 2007). The treadle-snare produced comparable injury scores to the Victor Soft-Catch trap (Meek et al. 1995, Fleming et al. 1998). Biochemical indicators of stress in red foxes captured by treadle-snares suggest higher levels of muscle damage, activity and dehydration (Marks, in review, Appendix 1). Given relatively low levels of impairment in locomotion using snares, a greater degree of activity may be possible, allowing greater acceleration and momentum and this could be implicated in trauma and stress (see Chapter 8.3). It is likely that the greater skill and familiarity required to use the treadle-snare effectively will result in outcomes that are less predictable than those from a simpler leg-hold trap mechanism.
The period of time that the animal spends in the trap is related to the injury and stress it sustains but the majority of studies fail to account for capture duration. Disregarding the influence of capture duration during trap studies often implies that a trap is expected to produce similar injury scores irrespective of the period of captivity. However, greater periods spent resisting the traps are known to contribute to overall trauma and are strongly linked to welfare outcomes. Stress such as anxiety, fear and a range of other pathologies cannot be measured by injury scores alone (see Chapter 5) and quantification of observed trauma as the primary welfare indicator has not fostered wider consideration of overall stress and welfare impacts. For example, tooth injury that exposes the pulp cavity has the capacity to inflict severe pain and debilitation in carnivores (see Chapter 6.2.1) and probably occurs relatively soon after capture. Rapid euthanasia of an animal that has suffered painful injury will deliver the best welfare outcome as this reduces the time period it remains in the trap and the potential suffering.
Trappers may be reluctant to adopt new trap designs that reduce injury unless they can be shown to have comparable efficacy to those in present use (Warburton 1982, Novak 1987). Although padded traps have been shown to be efficacious and humane relative to commonly used devices in North America, voluntary use of padded traps was reported to be low and the standard trap in use (in 1997) was the unpadded #3 coil spring trap (Hubert et al. 1997). Despite being available in the United States since 1984, padded traps in 1992 comprised only 3% of leg-hold traps owned by trappers (in Aldelt et al. 1999). Scepticism about research results and the increased cost of trap replacement (Phillips 1996), together with reports of lower capture efficacies associated with earlier models (Linscombe et al. 1988, Andelt et al. 1999) may account for poor adoption of padded traps in North America (Phillips 1996).
There is sufficient evidence to conclude the fourth generation Victor Soft-Catch traps (and possibly other devices such as the EZ Grip trap) have equivalent performance for the capture of canids with better welfare outcomes than unpadded traps.
8.0 METHODS TO IMPROVE WELFARE OUTCOMES
A range of modifications has been made to trapping devices and field practices to promote better welfare outcomes and target-specificity and these are summarised in Table 13. Major categories of modifications are discussed in this chapter with reference to the potential scope for improving the welfare outcomes of leg-hold trapping in Victoria.
8.1 Assessing trap performance
Evaluation of trap performance and routine testing of traps will reduce the likelihood of trap failure and poor welfare outcomes (Iossa et al. 2007). Closure speeds of traps will affect capture rates as some species are capable of recoiling rapidly (Johnson et al. 1986). The accumulation of surface soil and rust during the life of a trap increases the amount of friction that its springs need to overcome when triggered and indicates poor trap maintenance7. The mean trap closure speed of Victor #3 double coil and 3N long-spring traps was measured at between 18.59-18.52 mS (Johnston et al. 1986) and mechanical testing revealed that some Victor Soft-Catch #3 traps had insufficient clamping force to be effective (Earle et al. 2003). Replacement of springs in Victor Soft-Catch #3 traps or the use of additional springs was found to be necessary maintenance for traps used for dingo control (Lee Allen, personal communications). Excessive trap closure times increased trap injury scores and was associated with a greater number of bobcats being held by their toes rather than higher on their paw (Earle et al. 2003). Given the variability in testing conditions encountered in the field, standardisation of mechanical trap testing is required (Linhart et al. 1986).
Figure 10. Injury resulting from restraint by the digital pads from a padded steel-jawed (Lane’s) trap set in eastern Victoria in 2006. Trap closure speed will influence the position on the limb that animals will be held and slower closing devices are typically associated with capture by the digits and higher injury scores.
The performance of kill traps can be assessed in order to ensure their ability to cause rapid death for target species and the impact energy, trap closing time and clamping force are commonly assessed (Gilbert 1976, Zelin et al. 1983, Johnston et al. 1986). The development of performance criteria for kill traps for racoons, mink, muskrats, beaver (Gilbert 1976) and brushtail possums (Warburton et al. 1995, Warburton et al. 2000) enabled the development of traps that would produce rapid unconsciousness and death. The use of anaesthetised animals has been a standard practice in conducting these trials, yet it is probable that in some species these data may not reflect realistic times for loss of sensibility (Hiltz et al. 2001). Assessment of trap performance in an artificial setting cannot fully mimic the conditions and animal behaviours encountered in field situations. Kreeger et al. (1990) found that haematological, endocrine and biochemical indicators in wild caught red foxes varied significantly from those habituated and used in captive trials.
7 Standard operating procedures used for trap maintenance should include regular cleaning, boiling in dye and waxing before being reset in a new location. This procedure replaces human and/or canid odours with neutral odours and lubricates and protects traps from corrosion (Lee Allen, personal communication).
8.2 Trap inspection times
Increased periods of confinement in leg-hold traps are associated with correspondingly larger exertion, struggling and injury (Powell et al. 2003). Daily inspection of traps set for exotic brushtail possums in New Zealand is mandatory (Warburton 1992, Morris et al. 2003) under the Animal Welfare Act (NZ). In Sweden, trap inspection times must not be less than twice per day and this may account for the relatively low injury scores for foxes trapped in leg-hold traps and snares in the trial reported by Englund (1982). In the United States (in 1995), 33 states required that traps must be inspected every 24 hours. Early morning trap checking reduces the level of injury sustained by many trapped animals (Novak 1987, Proulx et al. 1994b, Andelt et al. 1999). Some researchers inspect traps twice each day in times of excessive heat (Logan et al. 1999) or early the following morning (Powell 2005). Trapping of species with high conservation value will often result in more attentive trap inspections such as the setting of traps at dusk and inspection and clearance at dawn (McCue et al. 1987).
During the harvesting of Arctic foxes using # 1½ steel-jawed traps, daily inspection was associated with 2/97 (2%) trap deaths compared with 14/58 (24%) deaths where foxes had been held longer (Proulx et al. 1994b). In most studies, the period that animals have been held in the trap is almost always imprecise and based upon periods between inspections. Some Australian studies are notable in that they report inspections periods of 48 hours (Stevens et al. 1987), irregular inspection periods (Fleming et al. 1998) or fail to report inspection periods (Thomson 1992) (Appendix 3). McIlroy (1986) noted that trapping practice for dingoes in south-eastern NSW could be inhumane if traps are not visited each day.
Increasing the frequency of trap inspections and human presence at the trap site is thought to reduce trapping success for wild dogs and is one reason why frequent trap inspection periods are avoided by some trappers (Lee Allen, personal communication). There are no published studies that indicate the degree to which increased frequency of inspection affects trapping success. It should be noted that if traps are inspected at dawn and then at dusk the following day (ie. daily), inspection times may allow some 36 hours to elapse (Fox et al. 2004, Iossa et al. 2007). Daily (ie. once each 24 hour period) inspection appears to be a minimum accepted world-wide standard to reduce trapping injury and more frequent inspection regimes would produce correspondingly greater welfare benefits.
8.3 Trap anchoring
Leg-hold traps and snares can be attached to fixed anchor points or a ‘drag’ such as movable objects or a grappling hook. The primary welfare advantage of drags is that an animal can seek cover and there is less resistance when pulling at the cable (Kirkwood 2005). This may be important when traps are set in exposed locations that offer no shelter from the sun, especially in arid environments (Lee Allen, personal communication). However, drags allow some animals to move to areas where they cannot be found. Englund (1982) reported that 13% of foxes held in leg-hold snares moved the drag more than 500 m from point of capture. Some authors consider that the ability of animals to be tangled in snares and trap cables is exacerbated using drags and is responsible for major injury such as fractures and dislocations (Linhart et al. 1988, Logan et al. 1999, Powell 2005). It is likely that the attachment type most suited to a particular application will be dependent upon the habitat in which it is used and behaviour of the particular target and non-target animals. In some environments that do not have a suitable substrate to permit anchoring of trap stakes (such as loose sandy soils), a drag may offer the best welfare outcome if it is less likely that an animal will escape with a trap attached to its leg (Lee Allen, personal communication).
Body weight range may be an important influence on the trauma experienced from trapping (Seddon et al. 1999, Iossa et al. 2007). Many predators have evolved an ability to accelerate from a standing position at greater rates than prey species, so that a short and efficient chase allows them to capture prey without reaching top speed (McNeil Alexander 2006). In general, the smaller an animal’s mass the shorter the distance it will need to accelerate to its maximum speed. Over short distances, some species can accelerate by leaping, using the leveraging of muscle forces and the storage of elastic energy in tendons to produce significant momentum over a very short distance that is then resisted by the anchoring chain. The forces (F) measured in Newtons produced by an animal can be approximated from its mass (m) and acceleration (a):
F = ma
The momentum (p) is given by the relationship between mass and velocity (v), where acceleration is velocity / time:
p = mv
Macropodids such as the eastern grey kangaroo accelerate to 67 m s-1 and potoroos to 100 m s-1 before the ‘take off’ speed necessary to leave the ground is reached (Nowak 1991), yet a species of intermediate mass such as the racing greyhound reaches maximal horizontal acceleration of 15 m s-1 and can do so in the first two strides (Williams et al. 2007). If tethers that bring them to a sudden stop close to maximum acceleration and take off speed restrain animals, these forces will be transferred to them as the tether resists their forward momentum. These forces will be largely dissipated by mechanical stress upon their body and will be responsible for much of the trauma inflicted by leg-hold traps. Animals of significant mass that have relatively greater potential for rapid acceleration (such as macropods), will absorb greater forces by virtue of their ability to attain greater momentum. Animals cannot accelerate towards a maximum speed instantaneously and the degree to which they are able to accelerate will depend upon how impaired they are by the attachment of the capture device and the length of the tether that allows them to accelerate towards a maximum speed.
There appear to be four main approaches for minimising forces of momentum and injury;
- Reduce the restraining cable to the shortest length possible so that the potential for acceleration is minimised;
- Use a trap device that impedes the animal’s normal locomotion so that acceleration is reduced by disrupting normal gait;
- Attach the trap tether to a drag that allows part of the force developed by momentum to be dissipated by its resistance and elasticity;
- Use in–line springs in the restraining cable to absorb the kinetic energy that would otherwise be transferred to the animal.
It is possible that the treadle-snare does not restrict locomotion of some species as significantly as the Victor Soft-Catch leg-hold trap as the snare cable allows the foot or paw of the trapped animal to remain in contact with the ground and allows relatively normal locomotion.
Therefore, the treadle-snare permits far greater potential for an animal to accelerate and produce forward momentum, especially if the restraining cable is long (Marks, in review, Appendix 1).
Drags and in-line springs may permit the dissipation of kinetic energy and reduce the potential for injury, but they do so at a net energy cost to the animal, as work must be done to move the drag or resist the springs. Drags produce an inconsistent and unpredictable amount of resistance dependent upon their weight and the friction that they offer in the different environments in which they are used. Better welfare outcomes may be obtained if energy expenditure is minimised and there is less potential for an animal to become exhausted, hyperthermic, dehydrated or food stressed. Indications of muscle damage and dehydration in foxes and bears restrained by leg-hold snares suggest high levels of activity with consequent higher energy expenditure (Cattet et al. 2003; Powell 2005; Marks, in review, Appendix 1). Anchoring a trap with a short restraining chain has been described as a way to reduce energy expenditure, injury and dehydration in other studies (Table 13).
The specification of in-line springs in trap chains should be adequate to ensure that the large forces of momentum produced by macropods are based upon a realistic calculations of forces produced, given the length of the chain, potential acceleration and upper body mass. Adoption of in-line spring specifications that have been developed in North America are unlikely to have catered for species such as macropods that are capable of developing larger amounts of momentum over shorter distances. Macropodids are a very common non-target species in south-eastern Australia (Chapter 4: Table 2) and this warrants specific research to develop appropriate specifications for in-line springs.
Centre-anchored chains that attach to the base of traps permit swivels to operate more effectively than chains attached to the side of the trap and probably contribute to better welfare outcomes by reducing torsional resistance (Linhart et al. 1988, Hubert et al. 1997, Lee Allen, personal communication). Such modifications should probably be made mandatory for all leg-hold trap devices.
8.4 Deactivation of traps
Using video systems to monitor coyote traps in the USA, a temporal partitioning of target and non-target species activity was observed. Between 0600 hrs and 1800 hrs over 81% of potential non-target species were observed, corresponding to when no coyotes were recorded. The authors conclude that diurnally inactivated trap systems could exclude the majority of non-target species without affecting trap efficacy (Shivik et al. 2002) although a suitable inactivating mechanism to perform this was not specified. A temporal bias towards captures of dingoes was detected in one study that used a capture data logger on traps (Figure 11) (Marks et al. 2004). Other authors have suggested that desisting from trapping or deactivation of traps during temperature extremes could assist in reducing trap deaths (Logan et al. 1999, Pruss et al. 2002). Most of the non-target mammals identified (Chapter 4.2) in south-eastern Australia are nocturnal as appears to be the case with target canids in many regions, yet bird species such as emus, corvids and lyrebirds are strongly diurnal (Schodde et al. 1990) as are goannas (Cogger 2000) and their capture may be reduced by diurnal deactivation of traps. Frequent trap inspection periods are avoided by some trappers given the belief that this will affect trap success (Lee Allen, personal communication). The degree to which site disturbance from manual deactivation of traps may affect trapping success has not been the subject of any published studies.
Figure 11. Time of capture (hours EST) for dingoes (n=48) trapped with Victor Soft-Catch #3 traps at Bulloo Downs (Queensland) during the study conducted by Marks et al. 2004.
8.5 Trap noise
There have been no published studies that address the significance of trap noise after capture on welfare outcomes, despite acoustic stressors being well known to produce stress in a range of situations (Chapter 6.1.7). Acoustic stressors produced by treadle-snares relative to Victor Soft-Catch traps may be one reason to account for elevated haematological and biochemical indicators of stress in red foxes captured by the former (Marks, in review, Appendix 1).
8.6 Trap size and weight
Padded Lane’s traps were significantly less selective than Victor Soft-Catch traps and another three devices assessed by Fleming et al. (1998). Newsome et al. (1983) caught proportionately more large native animals in toothed Lane’s traps than in smaller Oneida traps8. Lane’s traps are 1.6 x greater in area when set than Oneida traps, with 383 cm2 and 240 cm 2 capture areas respectively (Newsome et al. 1983). Differences in capture rates could be accounted for by better selectivity given the relative sizes and shape of macropod feet and the size of the spread of the jaws. The weight of traps may also influence welfare outcomes; the increased weight of the EZ Grip padded trap compared to the Victor Soft-Catch #3 was suggested to be a possible reason for an observed increase in bone fractures (Phillips 1996). Selection of a lightweight trap system may make a significant contribution towards reducing injury, but this has not been investigated in any detail and warrants further research. Padding, lamination or other modifications made to large steel-jawed traps may have limited value if the trap weight and jaw spread is implicated in bone fractures (Figure 12).
Figure 12. Older styled (modified) long-spring leg-hold traps are substantially heavier and have a larger ‘jaw spread’ than many contemporary (coil spring) leg-hold trap devices. Their weight and tendency to catch animals higher on the leg appears implicated in increased fractures and amputations.
8 In this study, each device was used by a different group of trappers and the different field methods used to set these traps could have introduced an unknown bias.
8.7 Pan tension
Turkowski et al. (1984) found that increasing the pan tension to prevent smaller animals springing the trap could enhance the selectivity of coyote traps. The US Department of Agriculture (Animal Damage Control) mandated the use of pan tension devices on all their leg-hold traps (Phillips et al. 1996a). Animals of comparable weight to target coyotes such as bobcats, porcupines (Erethizon dorsatum) and racoons are not generally excluded by pan tension devices. Overall, leaf spring tension devices were able to exclude 100% of smaller non-target species (by increasing pan tension to approximately 1.4 – 1.8 kg for coyotes), compared to only 6% exclusion by a standard trap set. This was found to reduce the potential capture rate of coyotes only marginally (CR = 0.92 v CR = 0.98) when compared to a standard trap device (Turkowski et al. 1984). The Paws-I-Trip® pan tension device (and other devices such as the ‘Stirling Pan System’) can be fitted to a range of traps and adjusted to provide a variable pan tension. Non-target exclusion rates for Victor Soft-Catch #3, Victor 3NM and Newhouse #4 traps were 99.1%, 98.1% and 91% and while exclusion was lower for heavier non-target species, rabbits and hares were excluded on 98.6% of occasions (Phillips 1996). Incorrectly set tensioning devices may exclude the capture of some coyotes, but given that non-target animals were captured far less often, the overall trapping efficacy was increased because more traps were unoccupied and required reduced effort to reset and release non-target species (Turkowski et al. 1984). Assessment of the Paws-I-Trip pan tension device suggested that its use on three types of traps did not adversely affect the performance of the traps (Phillips 1996).
Body weight differentials between species may be some guide to the potential success of pan tensioning systems, but should be used with caution in predicting selectivity. Other factors such as locomotor patterns (eg. quadrupedal or bipedal locomotion) and weight distribution vary between species (Turkowski et al. 1984). However, based upon the upper weight range of non-target species alone (Chapter 4.2: Table 2) it is possible that non-target species such as wallabies, kangaroos, wombats and goannas may overlap in weight with wild dogs and fail to be excluded by pan tensioning.
Pan tensioning is one of the most well proven, practical and inexpensive ways to increase target-specificity and promote better welfare outcomes of trapping. It will be most effective if applied to standard trap types and trap setting procedures and if based upon empirical studies that seek to understand the most appropriate trigger forces that allow reliable capture of target species and exclusion of non-targets. Temperature variation and wear from constant usage can influence the reliability of a trap trigger mechanism (Drickamer et al. 1993). Regular assessment of the performance of pan tensioning devices should be undertaken in the normal maintenance of overall trap performance.
8.8 Tranquilliser Trap Device (TTD)
The tranquilliser trap device was developed to eliminate or reduce injuries sustained by coyotes in steel-jawed traps that were the result of the animal’s struggle to escape the trap (Balser 1965). Delivery of diazepam (Balser 1965) and propiopromazine (PPZH) (Linhart et al. 1981) by TTDs reduced the extent of foot injuries received by coyotes captured in leg-hold traps. Additional trials have shown that PPZH delivered by TTDs reduced the severity of limb injuries sustained by grey wolves (Canis lupus) (Sahr et al. 2000) and tabs used on neck snares containing diazepam reduced the degree of facial injuries and oral laceration associated with coyote captures with neck snares (Pruss et al. 2002). Appropriately selected drugs may have the potential to depress the activity of captive animals and reduce tooth damage and limb trauma that is a consequence of repeated pulling and biting at traps. Dingoes caught in traps fitted with a TTD containing diazepam were found to have sustained tooth damage that was not significantly different from the placebo group. Neither the duration of capture nor mean activity was related to the tooth damage sustained by each dingo. Drug TTDs reduced limb damage and produced a lower injury score overall, but this was not statistically significant when compared to the placebo group (Marks et al. 2004). These data suggested that much of the tooth damage and limb injury sustained by trapped dingoes may occur quickly after capture when activity levels (in the placebo group) are up to four times greater than in subsequent hours. From the time of capture, drug onset is unlikely to be rapid enough to prevent tooth damage unless it can be greatly accelerated (Marks et al. 2004).
Drugs that reduce anxiety may mitigate distress associated with capture and drug choice will be important to ensure a beneficial reduction in anxiety and fear. It is thought that all vertebrate species possess specific receptor sites for benzodiazepine drugs, which influence states of anxiety (Rowan 1988). For diazepam, receptor affinity correlates well with behavioural potency and includes anxiolytic, sedative-hypnotic, muscle relaxant and anticonvulsant effects (Feldman et al. 1996). Moe and Bakken (1998) used an intramuscular dose of 5 mg kg-1 of diazepam, which resulted in mild sedation and did not appear to affect co-ordination but successfully reduced stress-induced hyperthermia in foxes. An oral dose of 10 mg kg-1 apparently produced heavier sedation, accompanied by an obvious loss in coordination (Marks et al. 2000, Marks et al. 2004). It is reasonable to assume that diazepam used in prior TTD studies (Balser 1965, Pruss et al. 2002, Marks et al. 2004) provided anxiolysis without any observed mortality from drug toxicity. Phenothiazine tranquillisers (ie PPZH) block dopamine receptors, have anticholinergic, antihistamine, antispasmodic and αadrenergic blocking effects and are widely used as sedatives (Plumb 1999). Some of the drugs in this group may be a poor choice for managing fear and phobia related behaviours and may produce sedation without or with limited anxiolysis. Acepromazine (a phenothiazine drug similar to PPZH) failed to reduce indicators of stress in dogs during air transport and this suggests that dogs were able to perceive stressors despite a reduction in behavioural indicators, misinterpreted as reduced fear and anxiety (Bergeron et al. 2002). While drowsiness, ataxia, reduced activity and less injury have been observed in trapped animals dosed with a TTD containing PPZH, it is possible that the drug does not reduce the experience of fear and anxiety, despite sedation. However, in other studies acepromazine has been shown to reduce indicators of stress associated with the capture of chamois (Rupicapra pyrenaica) (Lopez-Olvera et al. 2007). It appears that one of the major criteria for the selection of PPZH over diazepam as an active TTD drug was that it is not a controlled substance in the USA, unlike diazepam (Zemlicka et al. 1991).
The use of the TTD may have significant advantages for increasing the efficacy of trapping. Coyotes that had been captured by the toes were recovered on traps that had TTDs fitted, while it was thought that they would have escaped capture without it. Other advantages included the ability to release domestic or ‘recalcitrant’ dogs that have been captured, although tame dogs were not found to be as inclined to take TTDs as wild dogs (Balser 1965).
8.9 Lethal Trap Device (LTD)
Drugs used in the TTD may not have rapid enough onset to prevent some significant injury (Chapter 8.8) within the first hour and the drug may abate after 24 hours or in response to poor dosage. As captured dogs will ultimately be killed in most cases in south-eastern Australia, better welfare outcomes may be produced if this happens quickly after capture. Strychnine-impregnated cloth attached to jaw-traps has been used to achieve this in NSW, WA and QLD. Although potentially rapid, strychnine is inhumane and has become less favoured for this purpose (Fleming et al. 2001), partly because ingestion of sub-optimal quantities of strychnine cause an extremely painful toxicosis that may not be lethal for many hours. An alternative lethal trap device (LTD) formulation was proposed that causes the rapid death of trapped dogs and foxes (Nocturnal Wildlife Research Pty Ltd). Essentially it is the same device as a TTD, but with a rapid acting poison replacing the use of a tranquilliser drug.
8.10 Trap signalling devices
Reducing the time period that target or non-target animals remain trapped in a leg-hold trap will influence the degree of physical trauma and stress associated with trapping. Properly padded leg-hold traps seldom cause visible physical injury upon activation, but trauma is progressively accumulated over the period of captivity as the animal resists the trap (Proulx et al. 1993). Daily or even twice daily monitoring of traps is a standard practice for wildlife research and pest control work (Andelt et al. 1999, Larkin et al. 2003). Frequent trap inspection and human presence may reduce trapping success (Lee Allen, personal communication) and some trap signalling devices were constructed to reduce the necessity to closely approach and visually inspect trap sets for wild dogs (Marks 1996). To facilitate the rapid recovery of trapped animals, a range of radio-signalling devices have been developed to use in conjunction with traps (Nolan et al. 1984, Kaczensky 2002, Marks 1996, Larkin et al. 2003) and at least one purpose built device is commercially available (www.britishmoorlands.com), as are simple systems that are modified radio tracking transmitters used for wildlife studies (eg. www.avminstrument.com/transmit.html).
Trap signalling devices may theoretically assist rapid trap attendance, reduction in the overall time an animal is held and the period between capture and euthanasia or release. However as the majority of activity after capture appears to occur in the first few hours after capture in the dingo (Marks et al. 2004) and red fox (Kreeger et al. 1990, White et al. 1991), physical trauma such as tooth damage is probably acquired within the first hour of capture (Marks et al. 2004). The onset of capture myopathy in susceptible species is equally rapid (Chapter 6.2.3) and it is unlikely that signalling devices would promote a rapid enough response to reduce either of these major welfare impacts.
In east-central Illinois, radio monitoring systems allowed recovery of trapped animals in a mean of 18.3 minutes, opposed to mean capture times of 8.8 hours from trap inspections each 12 hours (Larkin et al. 2003). This was achieved by using constant operator vigilance of a cluster of traps deployed in a discrete area for diurnally active species. The largely nocturnal activity associated with foxes and some dingoes as well as the majority of the common non-target species (Chapter 4: Table 2) indicates that the majority of captures will occur during the evening. Monitoring of dingo captures using padded Victor Soft-Catch traps showed that there were clear nocturnal peaks in trapping success that were probably associated with dingo activity rhythms (Figure 11). Accordingly, if trap monitoring and attendance does not occur during evening hours, it is probable that a trap signalling device will have significantly less impact upon the time the animal spends in the trap and consequent welfare benefits.
8.11 Lures, odours and attractants
The detection and acquisition of prey in canids relies primarily upon visual (Mason et al. 1999), auditory (Gese et al. 1996) and chemical/olfactory (Bullard et al. 1978a) cues. Colour cues appear to be important in promoting the detection of lures, probably by allowing for more contrast against a particular background (ie. dark soils or snow) (Mason et al. 1999). Chemical/olfactory lures have been important components of trapping that increase the efficacy and capture rates of traps for coyotes. Most have been developed from blends of biological tissues and fluids (Turkowski et al. 1983) that are not easily replicated and this makes quality control difficult. It had been noted that volatile compounds of fox urine were powerful herbivore repellents and experiments sought to produce synthetic fermented egg compounds as carnivore attractants (Bullard et al. 1978a, Bullard et al. 1978b). These and other egg products were shown to be effective as repellents of rabbits, swamp wallabies (Marks et al. 1995) and brushtail possums (Woolhouse et al. 1995). Assessment of synthetic coyote attractants have shown an ability to influence the release of specific behaviours (Kimball et al. 2000). Wolf and dog faeces have a repellent effect upon sheep and the identification of the active components has been attempted in order to develop repellents for ungulates (Arnould et al. 1998). A generalised avoidance of predator faeces by prey species was suggested as a common adaptation for potential prey species (Dickman et al. 1984). Appropriate trap selection and canid-specific lures were believed to be responsible for the high degree of target selectivity in coyote control programs in Texas (Shivik et al. 2002). The concentration and amount of the lure used on traps may have important implications for the repellence of macropods and attraction of canids in Australia (Lee Allen, personal communication).
Predator odours have not always been shown to exclude herbivores; there was no apparent avoidance of fox scented traps by bush rats (Rattus fuscipes) and this suggested that naive prey species may fail to recognise odour cues from some exotic predators, due to the lack of extended periods of co-evolution and selection of predator avoidance strategies (Banks 1998). Native rodents avoided quoll faeces on 75% of sampling occasions, and a long coevolutionary history exists between these species (Hayes et al. 2006).
The potential exists for lure and repellent compounds (perhaps from native carnivores) to increase the target specificity of carnivore trapping, while repelling native herbivores, such as macropods and wombats from trap sets. Successful repellence of native herbivores could be a major advance in limiting the capture of non-target herbivores that constitute the most significant non-target cohort in Victoria. The use of predator attractants has largely been applied in an ad hoc manner, yet systematic and standardised collection of trapping data in field assessments could be used to assess a range of available carnivore attractants. Alternatively, simple experimental procedures could be applied to rapidly assess the efficacy of herbivore repellents.
8.12 Euthanasia or release?
The most important issues concerning euthanasia relate to the particular species and circumstances under which euthanasia is appropriate and the manner in which it is undertaken.
Target species will be euthanased as soon as possible upon inspection of traps. Non-target species should be either released or euthanased depending upon the level of debilitation they have suffered, as well as a decision based upon the likelihood that non-visible debilitation has occurred that will produce suffering after release. Macropodids and birds may be highly susceptible to capture myopathy and in the absence of knowledge concerning the pathophysiology of the disease in many species, they should be euthanased if it is suspected. It is unclear how other common non-target species such as wombats and possums are affected by capture myopathy and if they have the capacity to survive without suffering if released. If removal and release of some non-target species is envisaged, appropriate training and equipment should be considered. Necrotic pathology that may arise from periods of ischemia cannot be easily predicted from gross observation of an animal’s limb (Chapter 6.2.1). While this is less of a welfare issue if the animal is euthanased immediately, released non-target animals may become debilitated subsequent to release. Routine use of Heparinoid® cream prior to the release of radio-collared dingoes appeared to reduce swelling, bruising and potential necrotic conditions (Byrne and Allen 2008). Post-capture care can include treatment with antiseptics and long-acting antibiotics (Fuller and Kuehn 1983). Relatively simple post-capture treatments may significantly improve the prognosis of released non-target animals and it is appropriate that veterinary advice is sought, and where treatments are practical and beneficial, they are used routinely.
The American Veterinary Medical Association’s panel on euthanasia states that euthanasia techniques should result in rapid unconsciousness followed by cardiac or respiratory arrest and the ultimate loss of brain function (Andrews et al. 1993). There is debate concerning what techniques of euthanasia are acceptable to kill trapped animals. An extreme example of this issue is the use of trap sets that cause the drowning of animals after capture. They are considered to be unacceptable because it takes many minutes for some species to be rendered unconscious and EEG signals may last for up to 8 minutes (Ludders et al. 1999). Some authors have noted the practical limitations and safety risks of using euthanasia techniques in the field that might otherwise deliver more ideal welfare outcomes in a clinical setting (Bluett 2001). Many recommendations on methods to kill furbearing animals are made in order to protect the quality of the fur and drowning, suffocation and clubbing are advocated rather than more rapid methods that may affect pelt quality. One of the limitations of the ISO trapping standards is the absence of guidelines for euthanasia (Iossa et al. 2007). In Australia, one of the suggested practices for the euthanasia of trapped wild dogs and foxes is use of a rifle shot to the head after approaching the trapped animal in a way that avoids unnecessary disturbance and stress (Sharp et al. 2005a; 2005b). This may be inadequate and impractical for the euthanasia of many non-target species and if used in urban and urban-rural fringe areas. For example, it is very unlikely that a shot to the head can be relied upon to kill birds (eg. corvids and lyrebirds etc) and smaller mammals, given the extremely small head size. Rapidly moving macropods, feral cats and foxes will also be difficult to euthanase by a shot to the head. While in theory distant points of aim using a rifle may reduce handling stress and attempted flight upon the approach to the trap site, it is unlikely to be practical in delivering reliable head shots, especially for smaller animals. The specification of firearm loads and calibres should be selected cautiously. For instance, a small calibre (eg. .22) rifle may not deliver a reliable and humane death for wombats at an appreciable distance (Marks 1998b). In dense vegetation and when an animal has concealed itself and the point of aim is unclear, this may necessitate an awkward and shallow aiming position. The safety of using long-arms is questionable in this case and handguns or shotguns with appropriate loads may be preferable and less likely to produce ricochets or explosive returns from rock and soil. Guidelines should be developed for practical and safe euthanasia techniques that are appropriate for each species and all commonly encountered field conditions.
8.13 Trap sets and target-specificity
The manner in which a trap is set is an important influence over target-specificity and humaneness. Powell and Proulx (2003) propose that important considerations include trap elements, trap location and whether a bait or trail set is used. Trap elements include pan tension (Chapter 8.7), ie. setting the pan at an appropriate tension for a particular target species, with reference to likely non-target species. Setting the trap in inappropriate locations where entanglement in vegetation may occur can result in injury (Mowat et al. 1994). Reduction of non-targets can be achieved by careful site selection so that waterholes, gully crossings, tracks and pads beneath fences frequented by non-target species are avoided (Sharp et al. 2005a; 2005b). Non-target captures will be dependent upon local knowledge of target and non-target species behaviour, lures and trap devices used, pan tensioning and field practices that can reduce non-target captures (Lee Allen, personal communication). Food baits and lures should be avoided in areas where scavenging non-target animals frequent (Sharp et al. 2005a; 2005b). Placing a trap in an inappropriate location or the use of animal carcasses as lures (Corbett 1974, Newsome et al. 1983) is known to be a major factor in encouraging non-target carnivore captures (Powell et al. 2003).
The behaviour of some non-target species may make them more susceptible to capture. The common wombat is known to use fecal pellets and urine to mark its range (Triggs 1988) and will do so on elevated points such as rocks, small logs and at the base of trees (Triggs 1988, Taylor 1993). At Tonimbuk (Victoria), wombats mark novel objects or those that have been disturbed, such as a moved log (C.A. Marks, unpublished data). Their propensity to mark areas of disturbance may promote their capture at trap sites that have been prepared by digging, clearing or movement of logs or if the trap is located at the base of a tree. The use of ‘stepping sticks’ placed to prevent an animal stepping on the trap jaws and to direct its path onto the trap pan is a common practice (Johnson et al. 1980, Mowat et al. 1994) and may promote the capture of common wombats. Brushtail possums would likewise be susceptible to traps located at the base of trees, as they frequently descend and spend a proportion of their time foraging on the ground (Strahan 1984).
Understanding the behaviour of individual non-target species is essential in order to avoid their capture. Local knowledge of trapping conditions and field skills developed in consultation with other trappers is an important component of training for trappers. Local conditions will often determine specific strategies that are adopted by trappers and it is unrealistic to expect that one trapping protocol will be appropriate for all locations. Forums for the exchange of information and peer review of trap setting techniques, as well as provision of appropriate scientific information will aid in fostering a positive and supportive culture of continuous improvement in trapping practices. This may be the most effective way to ensure that canid management and welfare objectives are addressed in trapping practices.
8.14 Trap modifications
There is potential to adapt and modify trapping devices and practices to increase effectiveness and positive welfare outcomes. Exploiting the differences between the physiology and behaviour of target and non-target species may lead to more target-specific control strategies (Marks 2001b). Problematically, much of the published literature indicates ad hoc field experimentation with inadequate experimental control and use of multiple or erratic variations in trapping practices. This does not permit a good scientific basis for assessment. Adequate strategic planning and experimental design is strongly indicated and requires the development of protocols for the collection of data that can be analysed, interpreted and used to promote better welfare outcomes.
Coil spring traps used to capture racoons were modified with a ‘guard’ or ‘double jaw’ to protect against self-directed biting and appeared likely to have reduced injury scores (although not conclusively) (Anon 2003). There is potential to develop a similar guard system to prevent macropods from triggering leg-hold traps (eg. Victor Soft-Catch #3 or #1 ½) by exploiting their elongated foot relative to that of wild dogs. Other modifications have sought to increase target-specificity by minor modifications to established practices. A snaring system used for the capture of snowshoe hares (Lepus americanus) permitted the release of the threatened American marten (Martes americana) in Canada (Proulx et al. 1994a) as snared martins behaved differently from hares and spun their body upon capture. An anchor mechanism that disengaged or broke due to this spinning motion enabled the snowshoe hare snare system to be target-specific.
Traps that have been modified to reduce injury to target species have also been found to be more efficacious. Egg traps (Egg Trap Company: Springfield, USA) were found to be a humane and effective alternative to leg-hold traps to capture racoons. They prevent self-mutilation as a guard prevents the animal from biting the trapped limb (Proulx et al. 1993b, Hubert et al. 1996) and were 1.04 – 1.46 times more effective at catching racoons than cage traps (Austin et al. 2004). Proulx et al. (1993) reported that this device did not cause appreciable limb damage after 24 hours of captivity and damage was reduced compared to Victor #1 coil-spring traps (Hubert et al. 1996). In addition, Egg traps appeared to be far more target-specific as they excluded some non-target species (eg. dogs) from accessing the trigger mechanism (Hubert et al. 1999). Relatively little damage has been demonstrated in opossums (n = 40) (Didelphis virginiana) when they were captured in the device that was set and inspected daily (Hubert et al. 1999).
8.15 Jaw off-set distance
The ‘off-setting’ of trap jaws by a set distance (so that they do not fully close) probably produces better welfare outcomes (compared to the same traps where trap jaws fully close) by reducing impact and clamping forces upon limbs. Trap jaws have been off-set by 6.35 mm (Unpadded Northwoods #3) (Houben and Holland 1993), 7.9 mm (Unpadded Northwoods #3), 6.4 mm (Unpadded Sterling MJ600) (Phillips et al. 1996) and 4.8 mm (Bridger #3) (Hubert et al. 1997). However, some authors found that padding without off-setting jaws provided superior welfare outcomes (Phillips et al. 1996). The practical distance that jaws can be off-set is limited by the need to ensure that the trap is capable of holding all target species, but there appears to be little empirical basis or evidence-based rationale for the upper limits of off-set distances that can be found in the scientific literature. A standard jaw off-set of ¼ inch is probably based on North American practices9 and it is difficult to recommend an absolute value for all traps that may apply to wild dogs and non-target species in Australia without the collection of relevant local data and with reference to variations in other trap specifications (eg. jaw width, impact and clamping forces, padding material etc). A comparative study of limb morphometrics and anatomy for target and non-target species could be used to suggest evidence-based estimates of jaw off-set distances. Setting maximum practical jaw off-set distances may allow some non-target species to escape traps (eg. corvids and brushtail possums) if restrained by their limbs.
9 Jaw off-set distances for the modified (padded) Bridger #5 is ¼ inch as currently used in Victoria.
Table 13. Summary of modifications made to leg-hold traps, leg-hold snares and neck snares and field practices (‘Modifications/Practices’) and the reduction (‘Reduces’) in welfare impact for trap types and target species.
| TRAP TYPE | TARGET | MODIFICATION/PRACTICES | REDUCES | AUTHORITY | |
|---|---|---|---|---|---|
| #1½ coil spring trap | Racoon | Procyon lotor | Addition of a foot-guard (‘double jaw’) | Injury from self-directed biting | Anon 2003 |
| #3 and #4 leg-hold traps | Wolves | Canis lupus | Use of propiopromazine TTD | Injury in target and non-target species | Sahr and Knowlton 2000 |
| #1½ steel-jawed leg-hold | Arctic fox | Alopex lagopus | Daily trap inspection | Serious injuries | Proulx et al. 1994 |
| #3½ EZ Grip | Coyotes | Canis latrans | Padded and more powerful jaw | Trap injury more than off-set and laminated jaws in similar devices | Phillips et al. 1996 |
| #3 leg-hold traps | Coyotes | Canis latrans | Centre mounted 90 cm long chains to anchor traps | Less injury than shorter non-centred anchor chains | Linhart et al. 1988 |
| #4 and #14 Newhouse steel-jawed traps | Wolves | Canis lupus | Use of long-acting antibiotics | Risk of bacterial infections | Fuller and Kuehn 1983 |
| Aldridge snare | Black bears | Ursus americanus | Spring loading of snare cable | Abrupt stop and injury | Powell 2005 |
| Aldridge snare | Black bears | Ursus americanus | Snares set so that cables cannot tangle in foliage | Tangling and injury | Powell 2005 |
| All | Marten | Martes americana | Deactivation of traps during adverse weather | Hypothermia and hyperthermia | de Vos et al. 1952 |
| All | All | Frequent trap inspection | Injury | Proulx et al. 1993 | |
| All | All | Use of radio system to alert trap activation | Restraint time and injury | Marks 1996, Kaczensky et al. 2002, Larkin et al. 2003 | |
| Egg trap | Racoon | Procyon lotor | Guard does not allow racoon to access trapped limb | Self mutilation | Proulx et al. 1993, Hubert et al. 1996, Austin 2004 |
| Egg trap | Racoon | Procyon lotor | Guard covers limb caught by trigger mechanism | Non-target species (eg dog) captures | Hubert et al. 1996 |
| Egg trap | Racoon | Procyon lotor | Trap anchored to a tree above ground level | Self-mutilation as animals could not use captured limb for support | Poulx et al. 1993 |
| Foot-hold snares | Lynx | Lynx rufus | Use of multiple swivels on trap anchor cables | Injury from twisting and tangling in cable | Logan et al. 1999 |
| Foot-hold snares | Lynx | Lynx rufus | Careful site selection to reduce entanglement in vegetation | Injury from vegetation | Logan et al. 1999 |
| Foot-hold snares | Red fox | Vulpes vulpes | Plastic coating of snare cable | Foot injury | Englund 1982 |
| Leg-hold snare (Margo) | Grizzly bear | Ursus arctos | Short anchor cable | Muscle damage to limb | Cattet et al. 2003 |
| Leg-hold snare (Margo) | Grizzly bear | Ursus arctos | Short anchor cable | Dehydration | Cattet et al. 2003 |
| Leg-hold traps | Coyotes | Canis latrans | Use of Paws-I-Trip pan tensioning device | Non-target captures (reduced by 91- 99.1%) | Phillips and Gruver 1996 |
| Leg-hold traps | Coyotes | Canis latrans | Deactivate traps during diurnal periods | Non-target species (80%) not active | Shivik and Gruver 2002 |
| Neck snare (lethal) | Snowshoe hare | Lepus americanus | Coil attachment/anchor point | Allows American marten (non-target) to escape | Proulx et al. 1994 |
| Neck snares | Coyotes | Canis latrans | Use of diazepam tabs on snares | Facial and oral lacerations | Pruss et al. 2002 |
| Neck snares | Coyotes | Canis latrans | Use of obstacles to divert ungulate non-targets | Non-target capture | Pruss et al. 2002 |
| Neck snares | Coyotes | Canis latrans | Snare lock set to 27cm | Capture of ungulates | Pruss et al. 2002 |
| Northwoods #3 offset jaws | Coyotes | Canis latrans | Lamination, offset jaws and replacement springs | Reduce all injuries relative to standard trap | Houben et al. 1993 |
| Northwoods #3 offset jaws | Coyotes | Canis latrans | 0.635 cm lamination and additional spring tension | Injury scores reduced by 5-7.5 times that of Victor #3 coil or long spring traps | Houben et al. 1993 |
| Oneida #14 jump traps | Dingo | Canis dingo | Use of smaller Oneida traps compared to Lane’s trap | Non-target captures (large marsupials protected wildlife) | Newsome et al 1983 |
| Plastic Nordic Sport AB snare | Red fox | Vulpes vulpes | Use of snare in place of leg-hold traps | Tooth damage | Englund 1982 |
| Rose leg cuff | Badger | Meles meles | Use of Kevlar cuff to hold limb | Injuries other than temporary swelling of limb | Kirkwood 2005 |
| Snare | - | - | Increase diameter of snare cable | Injury | Garrett 1999 |
| Soft-Catch #1½ | Red fox | Vulpes vulpes | Use of padded trap | Physical trauma | Kreeger et al. 1990 |
| Steel-jawed trap | Fox | Vulpes vulpes | Padding of trap jaws | Fractures and joint injuries | Tullar 1984 |
| Victor long-spring #2 and #3 | Red fox | Vulpes vulpes | Plastic coating of traps | Tooth damage | Englund 1982 |
| Victor Soft-Catch #3 | Lynx | Lynx rufus | Pan tension set to 1 kg | Reduced small mammal capture | Mowat et al. 1994 |
| Victor Soft-Catch #3 | Lynx | Lynx rufus | No trapping in winter or when temp below -8 - oC | Freezing injury | Mowat et al. 1994 |
| Victor Soft-Catch #3 | Lynx | Lynx rufus | Fixed anchor, good quality shock absorber, short chain and 2 swivels | Entanglement, dislocation and fracture | Mowat et al. 1994 |
| Victor Soft-Catch #3 | Lynx | Lynx rufus | Increased jaw closure velocity, clamping force and impact force | Injuries and maximise restraint proximal to interdigital pad | Earle et al. 2003 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Replaced #1.75 springs with #3 springs | Mean trap-injury scores | Linhart et al. 1988 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Supplementary springs added | Trap related injuries | Gruver et al. 1996 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Increased spring tension by 40% | Reduction in injury score over other studies | Houben et al. 1993 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Use of padded trap | Limb injury | Linhart et al. 1986 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Use of pan tension device (0.9-1.4 kg tension) | Most non-target animal captures | Phillips et al. 1992 |
| Victor Soft-Catch #3 | Coyotes | Canis latrans | Reduced weight of trap compared to #3½ EZ Grip | Fractures | Phillips et al. 1996 |
| Victor Soft-Catch #3 | Dingo | Canis dingo | Use of diazepam TTD | Limb injury and activity | Marks et al. 2004 |
| Victor Soft-Catch #3 | Dingo | Canis dingo | Use of hepranoid creams on limb prior to release to restore blood flow | Pathology associated with ischemia | Byrne and Allen 2008 |
9.0 GENERAL CONCLUSIONS AND RECOMMENDATIONS
9.1 Recommended devices
- Large steel-jawed (eg. Lane’s type) traps cause much greater injuries to target and non-target species and are less target-specific than smaller leg-hold devices. Their relatively greater weight, large jaw spread and side-mounted chains result in poorer welfare outcomes than other devices. Padded large steel-jawed traps probably reduce injury to target and non-target species, but such modifications have received no detailed assessment. The use of large steel-jawed traps that are modified or unmodified should be discontinued as soon as possible.
- Laminated leg-hold traps have been found in some studies to reduce the incidence of trap related injury, when compared to non-laminated devices. Currently there is no clear scientific consensus that laminated traps have the potential to deliver better welfare outcomes than commercially available padded leg-hold traps. Lamination of existing leg-hold traps will not necessarily produce significantly improved welfare benefits.
- Treadle-snares are reported to require more skill to set, can be prone to misfiring and are bulky to transport. International literature suggests that in general, leg-hold snares are less effective than leg-hold traps for canid control. Some data suggests that treadle-snares cause greater stress to red foxes than other capture devices. The continued use of the treadle-snare should be reviewed with reference to these concerns.
- There appears to be potential for consistently better welfare outcomes using commercially available padded leg-hold traps such as the fourth generation Victor Soft-Catch #3 which can use short centre-mounted restraining cables, standard pan tension systems, are suited to the attachment of TTDs or LTDs, are familiar to trappers and are well supported by published data as effective in the capture of canids. Devices that conform to the ‘fourth generation’ of the Victor Soft-Catch #3 trap are probably current best practice for wild dog trapping. Victor Soft-Catch #1 ½ traps would be the most appropriate size trap for trapping red foxes.
- The Collarum non-lethal neck snare appears to have potential as a device that could find limited applications in urban and urban-rural fringe areas or where particular care must be taken in avoiding capture of non-target species. It may offer greater target-specificity and has potential to cause less major injury and death than padded leg-hold traps. Consideration should be given to trial then authorise this device if deemed appropriate.
9.2 Definition and regulation of leg-hold devices
- The definition of leg-hold traps as indicated in the POCTA rules should be extended to reflect commonly used scientific and commercial nomenclature and definition of leg-hold traps. Approved devices should be denoted by manufacturer, size and type and be stipulated in the rules.
- Regulations should seek to discourage the use of traps that have been modified in an ad hoc manner (eg. use of untested padding, lamination and arbitrary jaw off-set etc) and do not use objective and evidence-based data to support claims of efficacy and welfare outcomes. Traps should be maintained within the tolerances of a performance specification. However, it is appropriate that regulations do not inhibit future testing and continuous improvements to produce better welfare outcomes. Modifications and assessment should be supervised by competent oversight.
9.3 Development of trap specifications
- In order to promote current best practice and reliable welfare outcomes, mechanical trap specifications should be established that clearly define minimum performance based attributes. Important trap specifications should include trap size and jaw spread, trap weight, closure speed, impact force, clamping force, jaw offset distances, padding material (type, thickness etc) and pan tension characteristics. Ancillary features used with traps such as the type and number of in-line springs, swivels and anchoring methods should also be specified. A minimum benchmark for wild dog trapping could be based upon the fourth generation Victor Soft-Catch #3 trap using the manufacturer’s data or physical measurements.
- A number of rubber-jawed traps are on the market in Australia (eg. Duke ™ and Jake ™ traps) that have not been the subject of published research. The use of leg-hold traps that can be shown to conform or exceed the specifications established by the benchmark could be regarded as best practice. This would allow other manufacturers with trap products to certify their devices or adapt them to the benchmark if necessary. A benchmark could be a valuable tool to promote a culture of continuous improvement and further trap development.
- It would be appropriate for DPI/BAW to request assistance from companies involved in the manufacture of leg-hold devices and their Australian agents (eg. Woodstream Corporation: Pennsylvania for the Victor Soft-Catch #3 or the Livestock Protection Company: Texas for EZ Grip # 3½) to promote standardisation of traps for better target-specificity and welfare outcomes for Victorian and Australian conditions.
- North American humane trap standards have been developed for commercial fur harvesting and controlling wild dogs and are of some relevance to Australia. However, there are sufficient differences in the context of the wildlife management issues (eg. composition of target and non-target species, animal welfare legislation, etc) to justify developing unilateral specifications that address specific needs and requirements in Australia.
9.4 Improving welfare outcomes
- Trap specifications such as closure speeds and jaw spread may be essential to ensure that captured animals are consistently restrained above the interdigital pad in order to reduce injury from restraint.
- Adoption of in-line spring specifications that have been developed in North America are unlikely to have catered for macropods that are capable of developing large amounts of force through rapid acceleration and generation of momentum. The selection of in-line springs in trap restraining cables or chains should be based upon realistic calculations of the force that can be produced by macropods given the length of the chain, known acceleration and upper mass. Centre-anchored chains that attach to the base of traps permit swivels to operate more effectively than chains attached to the side of the trap and probably contribute to better welfare outcomes by reducing torsional resistance; they should be adopted as a standard practice.
- A positive relationship exists between the period of time held in captivity and the degree of injury and stress sustained. Worldwide, trap inspection periods of at least once per day are a minimum standard. Nocturnal animals are likely to experience additional stress if held for prolonged periods during the day. In the absence of novel ways to demonstrably improve the welfare of animals held for periods in excess of one day, trap inspection periods should be at least once per day to conform to a minimum accepted standard.
- During specific times of the year in eastern Victoria, when peak daytime temperatures are in excess of 30oC, trapping should be discontinued or all trap inspections should be completed well before peak daytime temperatures are reached. The relative lack of arid-adapted species in the eastern highlands of Australia and frequent capture of non-target species that are susceptible to thermal stress requires greater consideration than is appropriate for other Australian habitats.
- Various studies have contrasting recommendations concerning the merits of fixed trap anchoring or ‘drag’ fixed trap restraints. There is evidence that short chains and fixed anchoring points may provide better welfare outcomes. Drags may be appropriate when it is unavoidable to set traps in exposed locations that offer no shelter from the sun in hot and arid environments or if soil substrates do not allow reliable anchoring. It would be appropriate to monitor welfare outcomes of both options for target and non-target animals and adopt the most beneficial practice for a range of conditions.
- The use of a TTD or LTD in conjunction with a leg-hold trap that meets best practice standards for welfare outcomes should be pursued. The successful implementation of such devices would eliminate or mitigate the majority of stressors experienced by wild dogs and red foxes and greatly improve the welfare outcomes of trapping. As either device will not be beneficial for most non-target species, the best welfare outcomes of this approach overall will be produced if ways to improve the target specificity of traps are also pursued.
- The investment in a trap alert system might be warranted if it promotes rapid trap attendance, more frequent trap inspection and significant welfare benefits. As many target and non-target species are nocturnally active, unless 24 hour monitoring and recovery is proposed the welfare benefit is reduced. Frequent trap inspection and human presence may reduce trapping success and inexpensive and low power trap signalling devices may be a practical option to monitor the capture status of traps over a short monitoring distance that avoids close approach to the trap set if more frequent inspections are made. As much of the trauma of trapping is likely to occur within the first hour(s) of capture, the welfare benefit of this approach should be assessed with reference to other measures that could promote more cost-effective welfare outcomes.
- A clear policy dictating the fate of non-target species upon recovery should take into account the likelihood that many trapped animals have suffered debilitation that is not visible. Macropodids and birds are highly susceptible to capture myopathy and it would seem inappropriate that after prolonged capture they are released, since suffering or death due to debilitation is highly likely. A range of other species may be susceptible to capture myopathy, yet insufficient published information exists to produce a comprehensive assessment.
- If some non-target species are to be released from leg-hold traps or snares by a single person, the risk of operator injury is significant. Practices that are used to release non-target species should be reviewed and appropriate equipment and training needs considered to ensure that the pre-conditions that warrant euthanasia or release are known, and if release is attempted it can be done so safely and humanely.
- Recommendations for the use of firearms to euthanase non-target species should be reviewed as it is likely that current recommendations will not produce consistent outcomes in some non-target species nor will they be appropriate and safe in all environments.
- Standard jaw off-set distances of ¼ inch are probably based on North American practices. A comparative study of limb morphometrics and anatomy for target and non-target species could guide evidence-based estimates of jaw off-set distances for Australian conditions. Setting maximum practical jaw off-set distances may allow smaller non-target species to escape traps if restrained by their limbs.
- The routine use of post-capture treatments such as Heparinoid cream to reduce swelling, bruising and stimulate peripheral blood flow in released non-target animals shows potential to improve welfare outcomes. Veterinary recommendations concerning appropriate post-capture treatments (which may also include the use of antibiotic and antiseptic agents) for all animals prior to release should be developed and used as a mandatory procedure. Research should be undertaken to determine the relative benefit of such practices.
9.5 Improving target-specificity
- Pan tensioning is a well established technique to reduce the capture of non-target species that apply less ‘trigger force’ to traps than wild dogs. The use of pan tension systems should be a mandatory requirement for all leg-hold traps.
- It is essential to ensure that pan tensioning specifications are based upon evidence-based studies relating to the force applied by non-target species relative to target species and that periodic monitoring and adjusting of pan tensions for traps is undertaken as part of a quality control process.
- Canid lures and/or some odours associated with marsupial carnivores may be repellent to marsupial herbivores (eg. kangaroos, wallabies and wombats) that are the primary native non-target species in Victoria. Field assessment of lures and their potential to reduce non-target captures at a range of concentrations should be conducted in the eastern highlands of Victoria.
- Trap size and jaw spread appears to affect the incidence of non-target captures and is probably an important way to limit capture of macropods and other species. There is no compelling evidence to suggest that canid capture rates and trap efficacy are significantly reduced by using leg-hold traps that have a reduced jaw area/size. Traps used in Victoria should be limited to trap sizes no greater than a size typically cited as #3 (ie. 15 cm jaw spread) for wild dogs and # 1 ½ for red foxes (ie. 13 cm jaw spread) in order to limit non-target captures. Research should seek to test if more durable smaller trap devices can be produced to offer increased target-specificity in some circumstances without a reduction in capture rates.
- There are significant differences in the locomotion and foot anatomy of macropods and wild dogs and it may be possible to produce trap configurations that enhance target-specificity.
- There is a substantial published scientific literature concerning the development and assessment of trapping devices and practices to improve welfare outcomes and target specificity. It would be appropriate for this resource to be summarised and communicated in a relevant way to people involved in trapping. Training in the nature of stressors, stress and pathology associated with traps in a range of species would be useful.
- Knowledge of specific behaviours of key non-target species may allow trappers to develop strategies to further minimise their capture. The abundance and diversity of non-target species in different habitats is an important consideration. A practical summary of the behaviour of key non-target species based upon a synthesis of trapper field skills and scientific studies may assist in training, as well as sharing knowledge with members of the public that also undertake trapping.
9.6 Assessing comparative welfare outcomes
- Adoption of a standardised protocol to test welfare impacts of different traps and trap modifications is required to assist in continuous improvement of trapping practices. This standard would be most useful if it were adopted nationally.
- One of the chief problems associated with the assessment of welfare outcomes of trapping in the field is that the period an animal has remained in the trap is rarely known with any accuracy. The use of inexpensive timer/activity monitoring modules should be attached at least to a sample of routinely used traps. Data collected would include capture duration, time of the day that species are likely to be caught and the degree of activity and struggling associated with different species and devices.
- The most unequivocal insight into the comparative welfare impacts of traps is likely to be produced by physiological indicators (ie. CK, AST, ALP, ALT and N:L ratios) in concert with a standardised scoring of whole body injury from necropsies. The capture period and relative activity of animals must be known in conjunction with these measures to accurately assess welfare impacts.
9.7 Reporting research and assessment
- Licensed institutions that use leg-hold or other capture devices should be encouraged to report and/or publish details of trapping methods and results so that comparative data is produced for: location, habitat type, capture success, target specificity, injury to target and non-target species, trap inspection frequency and modifications made to trap devices. The development of a standardised reporting procedure could be an obligatory requirement under the auspice of AECs.
- A large amount of information has been collected during field trials of various trapping methods and using trap modifications in Australia and overseas. Much of this material is of limited value due to the lack of experimental controls, inadequate sample sizes, inconsistent application of methods or a reliance on subjective interpretation. A partnership between trappers and researchers should be fostered, when possible, to encourage future assessment of potential improvements to be appropriately rigorous.
9.8 Knowledge gaps
- As published studies are limited in their scope, advice should be sought from zoo veterinarians and keepers of Australian native fauna concerning the relative susceptibility of potential non-target species to capture myopathy. A schedule of appropriate actions concerning post-capture treatment and release or obligatory euthanasia should be prepared in order to guide the action of trappers.
- Pressure necrosis and ischemia may arise from the use of traps or leg-hold snares that restrict blood flow to tissues for prolonged periods. The incidence of ischemia produced by different padded and laminated traps is unknown and the short and long-term impact on welfare outcomes is unknown in target and non-target species. Nonlethal studies that monitor the short-term restriction of blood flow in anaesthatised animals in the laboratory may be adequate to predict the relative likelihood of ischemia arising from different trap devices.
- Most mechanical specifications for commercial traps used in Australia follow recommendations based upon North American experience. There is a need for empirical data to be collected locally to enable evidence-based adaptation of trapping methods to increase target specificity and promote better welfare outcomes.
Acknowledgements
The Bureau of Animal Welfare (BAW) of the Victorian Department of Primary Industries (DPI) commissioned this review. We express our foremost gratitude to Ms Jane Malcolm for her valuable support, superb editorial skills and assistance throughout. Our thanks to Mr Steven Moore (BAW-DPI) for supplying information about legislation governing the use of traps and snares in Victoria. Mr Frank Busana oversaw the photo-documentation of trapping injuries of foxes provided to the Victorian Institute of Animal Science (Frankston). Hayley Rokahr (Department of Sustainability and Environment) provided the data for non-target species distribution from the Victorian Wildlife Atlas. Mr Jim Backholer supplied a copy of his unpublished manuscript (Murphy et al. 1990) that is cited in this document. Mr Brendan Roughead provided clarification on trap types used in Victoria and the history of field practices and use of trap devices. A range of staff of DPI (Victoria) provided helpful information and we thank them for their assistance. Previous drafts of the manuscript benefited from constructive criticism and suggestions made by Dr Lee Allen (Robert Wicks Pest Animal Research Centre, Department of Primary Industries and Fisheries, Queensland), Dr Charles Hackman, Royal Australian and New Zealand College of Anaesthetists, Peter MacCallum Centre, Victoria), Ms Silvana Cesarini (School of Biological Sciences, Monash University, Victoria), Dr Kate Blaszak (former Principal Veterinary Officer, BAW) and Dr Graziella Iossa (Mammal Research Unit, University of Bristol, UK).
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Appendix 1.0
Haematological and biochemical responses of red foxes (Vulpes vulpes) to different recovery methods
Clive A Marks1
1Nocturnal Wildlife Research Pty Ltd, PO Box 2126, Wattletree Rd RPO, East Malvern, Victoria 3145, Australia
Abstract
Haematology and blood biochemistry profiles were produced for red foxes (Vulpes vulpes) recovered by either cage traps, treadle-snares, Victor Soft-Catch (VSC) #3 traps, netting or shooting. Compared to all other recovery methods, foxes captured in treadle-snares had significantly higher mean albumin (ALB), creatine kinase (CK), red cell count (RCC), neutrophil to lymphocyte (N:L) ratio, sodium (Na), total protein (TP) and white cell counts (WCC). Treadle-snares were also associated with higher chloride (Cl), haemoglobin (Hb) and packed cell volume (PCV) than cage trapping and netting. Treadle-snares produced indicators of greater muscle damage, exertion and dehydration compared to cage and VSC traps. These data do not support former studies that concluded that due to similar injury scores, treadle-snares and VSC traps produced equivalent welfare outcomes. Injury and death are end-points of poor welfare and monitoring stress using physiological indicators allows the relative potential for different recovery techniques to cause pathological and pre-pathological states to be compared. Different pest control and wildlife management techniques may vary greatly in the magnitude and nature of stress they produce and physiological indicators might be a highly informative way to investigate, qualify and rank relative welfare outcomes.
Keywords: Trapping, snares, foot-hold traps, leg-hold traps, stress, red fox, Vulpes vulpes
Introduction
The assessment of welfare outcomes arising from different leg-hold (or ‘foot-hold’) traps used for coyotes (Canis latrans), wolves (Canis lupus), dingoes (Canis lupus dingo) and red foxes (Vulpes vulpes) (collectively referred to as ‘canids’) has relied upon contrasting the extent of visible injuries assessed upon their recovery (eg. Tullar 1984; Van Ballenberghe 1984; Olsen et al. 1986; Onderka et al. 1990; Houben et al. 1993; Hubert et al. 1997; Phillips et al. 1996; Fleming et al. 1998). However, physical injury is only one indicator of the overall stress and potential suffering (Iossa et al. 2007). Trapping produces a wide range of stressors (Moberg 1985; Gregory 2005) and stress which if intense or prolonged can have negative impacts upon an animal's welfare (Jordan 2005). Anxiety may result from stressors such as abnormal light exposure, unfamiliar odours, aversive sounds and restricted movement (Morgan and Tromborg 2007). Limb oedema is frequently observed after trapping in leg-hold traps (Andelt et al. 1999), yet its relationship to the onset of ischemic injury cannot be easily predicted from gross examination, as necrotic tissue develops over many days or weeks (Walker 1991). Stress can produce pathology such as myocardial lesions and affect tissue integrity in vital organs (Sanchez et al. 2002) and increase the risk of infectious disease by reducing the effectiveness of the immune system (Raberg et al. 1998). Capture myopathy can cause chronic debilitation in some species and predispose them to morbidity and death weeks after capture (Hulland 1993). Dehydration caused by prolonged confinement and/or intense activity during captivity (eg. Powell 2005) is not frequently considered as a specific welfare problem associated with trapping.
Welfare indicators are required to assist with good welfare in conservation activities (Bonacic et al. 2003) and to support the development of more humane vertebrate pest control (Marks 2003; Littin et al. 2004; Littin and Mellor 2005). Physiological responses to different capture techniques have proved to be useful indicators for assessing welfare outcomes for red foxes (Kreeger et al. 1990a; White et al. 1991), kit foxes (Vulpes macrotis mutica) (McCue and O'Farrell 1987), African wild dogs (Lycaon pictus) (De Villiers et al. 1995), grizzly bears (Ursus arctos) (Cattet et al. 2003), black bears (Ursus americanus) (Powell 2005), river otters (Lontra canadensis) (Kimber and Kollias 2005), Eurasian otters (Lutra lutra) (Fernandez-Moran et al. 2004), brushtail possums (Trichosurus vulpecula) (Warburton et al. 1999) and koalas (Phascolarctos cinereus) (Hajduk et al. 1992). The International Standards Organization (ISO) Technical Working Group on Traps rejected the use of hormone and blood biochemistry to develop welfare indicators for canid trapping (Harrop 2000), yet many haematological and biochemical indicators are standardised, cost-effective and widely available. Currently there are few data on physiological responses to different traps (Powell 2005), especially for canids that continue to be the focus of on-going trapping in Australia (Saunders et al. 1995; Fleming et al. 2001; Allen and Fleming 2004) and the United States (Fox and Papouchis 2004).
Analysis of visible trauma scores after the capture of foxes and dogs led to the conclusion that treadle-snares were more humane (Stevens and Brown 1997; Fleming et al. 1998) or delivered approximately equivalent welfare outcomes to Victor Soft-Catch #3 (VSC) traps (Meek et al. 1995). As a range of trapping and recovery techniques were used during a study of urban red foxes in Melbourne (Australia), the influence of recovery methods upon haematology and blood biochemistry values were investigated and compared with published normal values or those reported after known periods of confinement in traps or after shooting. This paper sought to determine if common haematology and blood biochemistry values might assist in determining the relative welfare outcomes arising from different red fox recovery techniques and if the previous conclusions about welfare outcomes produced by treadle-snares and VSC traps were supportable.
Methods
Capture and recovery methods
All foxes were recovered from urban habitats within 20 km of central Melbourne, Australia (37.8° S 145.0° E) that were used in previously reported studies (Marks and Bloomfield 1998; 1999a,b, 2006; Robinson and Marks 2001). The treadle-snare (Glenburn Motors: Yea) and Victor® “Soft-Catch” #3 traps (VSC) (Animal Capture Equipment and Services: Warrick) were set as described by Meek et al. (1995), using fish-based cat food as a lure. The treadle-snare is shaped like a small banjo and has a circular pan or ‘treadle’ similar to the Aldridge snare (see Skinner and Todd 1990). A wire cable snare is placed around the pan and the snare is thrown up the animal’s limb, and tightened by a spring arm when triggered (Meek et al. 1995; Fleming et al. 1998). Cage traps measuring 1200 × 450 × 450 mm with a hook and modified floor press trigger (Wiretainers: Preston, Australia) or 1800 × 450 × 600 mm custom-made cage traps were baited with whole chicken carcasses. Traps were set on or alongside known fox trails, fences, gates, culverts or outside diurnal shelter sites that were typically beneath houses or on the periphery of patches of blackberry (Rubus fruiticosus agg.), wandering tradescantia (Tradescantia albiflora), African thistle (Berkheya rigida), fennel (Foeniculum vulgare) and introduced grasses (Marks and Bloomfield 2006). Traps were inspected at least every four hours during the evening and were de-activated during the day. Blood samples were opportunistically taken during fox control programmes that used terrier dogs to flush foxes from shelter sites into 1-m high, 50-m long micro-filament ‘gill nets’ that were set loosely surrounding diurnal shelter sites. A sample of shot foxes was taken at urban locations at the end of all research activities when this could be achieved safely. Sub-sonic .22 calibre ammunition was used with a Ruger 10/22 rifle that had been modified with a target-rifle barrel and fitted with a silencer and a telescopic sight. Foxes were head shot from a distance of < 25 m after being illuminated with a 100 W spotlight.
Sedation and blood sampling
Upon recovery, live captured foxes were covered with a hessian sack, restrained with a hand noose and dosed with an intramuscular injection of 10 mg kg-1 of a tiletamine/zolazepam combination (Zoletil®: Virbac, Australia), based upon an assumed adult median weight of 4 kg; this produced deep sedation and light anaesthesia. Tiletamine and zolazepam combinations have been used successfully for minor surgery in foxes without an indication that they caused significant alteration in haematology and blood biochemistry values (Kreeger et al. 1990b). A 30 mL sample of blood was taken from the jugular vein with a 1 x 30 mm (19G) needle and apportioned into 10 mL lithium heparin, EDTA and clot vacutainer tubes (Becton-Dickenson: Melbourne). Blood samples were taken close to the point of recovery usually within the first hour of capture and before the anaesthetic had fully abated. If anaesthesia was insufficient, an hour was allowed to elapse before administering the full dose again. After shooting, blood samples were taken by cardiac puncture immediately after death had been confirmed by the loss of corneal reflex. Vacutainers were transported to Dorevitch Pathology (Camberwell) at 0600 hrs the following morning for haematology and biochemistry analysis.
Statistical analysis and comparison with published data
Foxes were deemed to be adults if their weight exceeded 3 kg and they were at least 9 months old, based upon a minimum estimated age at the time of capture using August as the birth month in Melbourne (Robinson and Marks 2001; Marks and Bloomfield 2006). Residual data were stabilised by transformation if necessary, together with non-normally distributed data prior to analysis. Comparisons of recovery method with haematological and blood biochemistry values were analysed using a general linear model using the least significant difference (LSD) test for post hoc comparison. Relationships between adult fox gender, weight and recovery method were tested using binary logistic regression (SPSS version 16: SPSS, Chicago). Comparisons were made with published accounts of blood values following trapping in VSC traps, shooting (Kreeger et al. 1990a), cage traps (White et al. 1991) and normal blood data based upon sampling a mixed population of captive silver and red foxes (both V. vulpes) (Benn et al. 1986).
Results
A total of 125 foxes were recovered. Two were euthanased due to trapping injury (broken leg and trauma to the scrotum) and excluded from the sample, along with 35 juvenile foxes. Foxes recovered by either VSC traps or treadle-snares typically had mild oedematous swelling of the captured limb two hours after recovery but no injuries were detected in cage trapped or netted foxes.
A total of 88 adult foxes (female = 38, male = 50) had blood samples successfully analysed after recovery with cage traps (n = 8), netting (n = 17), shooting (n = 11), treadle-snares (n = 45) and Victor Soft-Catch traps (n = 7). There was no significant relationship between the recovery method and gender (ß = -0.28, Wald = 1.62, d.f. = 1, P = 0.760) or the mean weight of males (5.2 kg, sd = 1) and females (4.7 kg, sd = 1.44) (F = 1.9, d.f. = 1, P < 0.174). Inconsistent records for alkaline phosphatase and eosinophil values produced a small data set and precluded analysis. In the remaining data there were insufficient data to test responses due to sex and weight, data were pooled for analysis. Recovery methods had no significant effects upon bicarbonate, triglyceride, urea, mean corpuscular volume, mean corpuscular haemoglobin or platelets. Significant effects were detected for red cell count (RCC) (F = 17.7, d.f. = 4, P < 0.001), packed cell volume (PCV) (F = 19.1, d.f. = 4, P < 0.001), white cell count (WCC) (F = 15.5, d.f. = 4, P < 0.001), haemoglobin (Hb) (F = 3.07, d.f. = 4, P < 0.05), neutrophil to lymphocyte (N:L) ratio (F = 10.8, d.f. = 4, P < 0.001), albumin (ALB) (F = 21.8, d.f. = 4, P < 0.001), total protein (TP) (P = 20.0, d.f. = 4, P < 0.001), creatine kinase (CK) (F = 60.7, d.f. = 4, P < 0.001), sodium (Na) (F = 18.6, d.f. = 4, P < 0.001), potassium (K) (F = 15.5, d.f. = 4, P < 0.001) and chloride (Cl) (F = 3.3, d.f. = 4, P < 0.05).
Foxes captured in the treadle-snare had significantly higher mean ALB, CK, RCC, N:L ratio, Na, TP and WCC when compared to all other recovery methods. Compared to cage trapping and netting, treadle-snares were also associated with higher Cl, Hb and PCV values. Foxes captured in Victor Soft-Catch traps had significantly higher mean ALB and CK compared to shot foxes (P < 0.05) and higher mean CK values than observed in foxes that had been shot, netted or captured in cage traps (P < 0.01). Shot foxes had a significantly higher concentration of Na compared to those that had been captured in a cage trap (P < 0.01) or by netting (P < 0.01) (Table 1).
Discussion
What are appropriate physiological indicators of trapping stress?
Trappers were reported to inspect traps every 8 hours in Sweden (Englund 1982). In the United States (in 1995) 33 states required that traps must be inspected every 24 hours (Andelt et al. 1999), yet in Victoria (Australia) some trappers are compelled to inspect leg-hold traps only every 48 hours. Different trap inspection periods suggest that welfare outcomes for the same trapping devices may be correspondingly variable. Comparisons of injury data from different traps will only be valid if the mean period of captivity for any experimental group is not significantly different between or within studies that are compared. Few studies have sought to monitor the duration and changing intensity of struggling during captivity and then related this to welfare indicators and outcomes (Marks et al. 2004).
Activation of the hypothalamic-pituitary-adrenal axis and flight-fight response following capture causes a period of vigorous struggling that is likely to influence the degree of trauma experienced by foxes (Kreeger et al. 1990) and the onset of pre-pathological states. Struggling by foxes was intense immediately following capture in VSC #1 ½ traps, but decreased rapidly after the first two hours (Kreeger et al. 1990a). A similar pattern was observed for foxes captured in cage traps (White et al. 1991) and dingoes captured in VSC #3 traps fitted with activity monitoring devices (Marks et al. 2004). Foxes may adopt a strategy of conservation-withdrawal after some hours and a reduction in observed struggling with reduced potential for injury (Kreeger et al. 1990a).
Physiological measures that provide a generalised indication of the cumulative physiological and pathological impact of trapping must have sufficient persistence to be meaningful many hours after initial capture, in order to be useful indicators of welfare outcomes. While cortisol has been commonly used to investigate stressors (Carstens et al. 2000) and capture stress in dogs (De Villiers et al. 1995) and foxes (Kreeger et al. 1990a), sequential sampling may be required if stress response changes substantially during the period of capture. This is difficult to achieve in the field without introducing additional stressors from restraint, venipuncture or human presence (Beerda et al. 1996; Hennessy et al. 1998). Moreover, as the duration of a canid’s captivity is rarely known with accuracy, the magnitude of the cortisol response at recovery of an animal is of limited value as an indicator of overall stress, given that peak cortisol is usually achieved in minutes and may decline within an hour (Beerda et al. 1998).
Injection of corticosteroids or adrenocorticotrophic hormones in dogs was reported to cause an increase in neutrophils (N) and a decrease in lymphocytes (L) within 2 – 4 hours (Jasper and Jain 1965). Stress may reduce the number of neutrophils held in marginal pools in some species and increase the number of circulating neutrophils, but will be contingent upon the nature and intensity of a stressor (Oishi et al. 2003). The N:L ratio may not be immediately detectable after periods of stress, yet was informative about trapping stress in foxes (Kreeger et al. 1990a). Short-term mental stressors have also been shown to cause a significant increase in neutrophil activation (Ellard et al. 2001). Neutrophil counts were significantly increased while lymphocytes decreased in dogs subjected to air transport (Bergeron et al. 2002) and in coyotes following capture and restraint (Gates and Goering 1976). Monitoring neutrophil activation due to transport stress was found to be a useful welfare indicator in European badgers (Meles meles) (Montes et al. 2004). Leukocytes counts are subject to diurnal variation, with neutrophils typically peaking in dogs during the day, corresponding to a decline in lymphocytes which tend to peak during the mid evening (Lilliehook 1997; Bergeron et al. 2002) and this may be significant if small changes in N:L ratios are being monitored.
Creatine kinase concentrations are used for diagnosing skeletal muscle damage (Aktas et al. 1993). In rats, the concentration of serum CK correlated strongly with the volume of muscle traumatised by crushing injury (Akimau et al. 2005). Tourniquet ischemia of the arm produced with the application of a pneumatic cuff for one hour caused elevations in CK and TP in humans that could be detected for three days after its removal (Rupiñski 1989). Human patients that are manually or mechanically restrained respond with elevation in CK values (Goode et al. 1977) typically associated with muscle trauma (rhabdomyolysis), although shock, surgery or disease affecting the skeletal muscles (Prudhomme et al. 1999), myocardial damage (Moss et al. 1987) or prolonged and stressful exercise (Noakes 1987). Elevated CK was found in foxes captured in padded and unpadded leg-hold traps (Kreeger et al. 1990a), but not significantly in those captured in cage traps (White et al. 1991). Some stressors do not produce a significant increase in CK in some species or breeds (probably due to genotypic differences). In Alaskan sled dogs there was little indication of increases in serum CK after days of strenuous racing (Hinchcliff et al. 1996), yet elevation of CK is associated with physical exertion in most domestic dog breeds (Aktas et al. 1993). The reliability of CK as a specific marker for diagnosis of muscle disease (Auguste 1992, in Aktas et al. 1993) is also influenced by snake venom toxicosis, myocardial disease associated with parvovirus, dirofilariasis, haemolysis and venipuncture and interaction with some therapeutic agents (reviewed in Aktas et al. 1993). The progressive evaluation of recently captured river otters (Lontra canadensis) showed that CK was not a good indicator of musculoskeletal injury due to possible interactions with existing pathology independent of capture injury (Kimber and Kollias 2005). In flying foxes (Pteropus hypomelanus), anaesthesia with isoflurane (an anaesthetic) reduced the intensity of CK changes (Heard and Huft 1998).
Comparison of fox trapping data with other studies
Treadle-snares had a significantly greater effect upon blood values than VSC #3 traps and these data corresponded closely with those reported for foxes held in VSC #1 ½ traps for 8 hours for WCC, ALB, TP, CK, N:L and RCC (Kreeger et al. 1990a). Kreeger et al. (1990a) concluded that leg-hold traps produced a classic stress response characterised by an increase in HPA hormones, neutrophilia (high N:L ratio) and elevated CK, as well as other serum chemicals such as lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and aspartate aminotransferase (AST). Foxes captured using VSC #3 traps in the Melbourne study revealed similar shifts in ALB, CK, WCC and Na values that were intermediate between those found after 2 and 8 hour confinement in VSC # 1 ½ traps (Kreeger et al. 1990a). Similarly, foxes held in a cage trap for 8 hours (White et al. 1991) had higher mean values for ALB, CK, Hb, RBC and N:L ratio compared to those held for < 4 hours in cage traps in Melbourne. The standard errors observed for the mean blood values obtained from shot foxes in Melbourne overlapped with those reported by Kreeger et al. (1990a) and White et al. (1991) for CK, Na, TP and WCC, and closely approximated the ALB and N:L values. Blood PCV taken from shot foxes in the Melbourne study and by Kreeger et al. (1990a) were higher than normals reported by Benn et al. (1986) or those from cage trapped foxes and may be an artefact of blood sedimentation post mortem (Table 2).
In some species, excitement and strenuous exercise can cause contraction of the spleen and expulsion of erythrocytes into circulation (Wintrobe 1976) and this may alter normal RBC, Hb and PCV (Hajduk et al. 1992). Blood normals for captive-bred foxes had higher Hb and RCC and were attributed to splenic contraction as a stress response during blood sampling in manually restrained and unsedated foxes (Benn et al. 1986). Other studies have used transponder collars to remotely anaesthetise free-ranging animals prior to blood sampling (eg. Powell 2005) and this appears to provide less equivocal blood normals typical of unrestrained animals. Elevated TP in captive foxes could be due to a high quality artificial diet (Benn et al. 1986) or a genotypic consequence of selective breeding. Normal CK values were reported to be substantially lower in fox blood normals (Benn et al. 1986) and captive wild red foxes prior to surgery (Kreeger et al. 1990b). This is possibly because shooting trauma elevates CK values, as seen in shot pigs (Münster et al. 2001) and after brain gunshot trauma (Kaste et al. 1981) (Table 2).
Black bears captured in Aldridge snares had higher CK and ALB values and this was attributed to greater exertion, muscle damage and dehydration compared to values generated from individuals captured by remote activated tranquilising collars (Powell 2005). Elevation of CK has also been reported for polar bears captured in snares (Ursus maritimus) (Lee et al. 1977; Schroeder 1987; Hubert et al. 1997). Grizzly bears had higher N:L ratios, as well as increased concentrations of Na and Cl that were attributed to dehydration due to water deprivation over 2-23 hours of captivity in snares and this was probably aggravated by intense activity (Cattet et al. 2003). Increased CK, PCV, ALB, Na, TP and Cl in treadle-snare when compared to cage trapped foxes appears consistent with these profiles and is suggestive of dehydration due to intense activity in red foxes.
Why do treadle-snares cause a greater physiological response?
Treadle-snares require adequate clearance from obstacles to allow the mechanism to function without obstruction, whereas VSC traps could be placed closer to or beneath overhanging vegetation. Treadle-snares were tethered to a solid fixture by 2 m lengths of snare cable and chain, in contrast to 0.5 m chains that were used to anchor the VSC traps. The snaring mechanism allow the fox’s foot to remain in contact with the ground, so that they have the ability to run or leap to the end of the snare tether where they are brought to a sudden stop, while in VSC traps their coordinated movement appears to be impaired (C.A. Marks, personal observations). Many predators have evolved an ability to accelerate at greater rates than prey species, so that a short and efficient chase allows the predator to capture the prey without reaching top speed (McNeil-Alexander 2006). For example, racing greyhounds reach maximal horizontal acceleration of 15 m s-1 and can do so from a standing start in the first two strides (Williams et al. 2007). Being pulled to a sudden stop at higher speed may be associated with greater muscle damage, similar to the case hypothesised for Aldridge snares (Powell 2005) where constant tugging by bears captured in snares caused fractures, muscle, tendon, nerve and joint injury (Lemieux et al. 2006).
Traps have a wide range of moving parts with attachments, chains and mechanisms that produce a varying amount of sound when activated and resisted by captive animals. Loud noises were shown to be aversive to domestic dogs and affected gastric motility and hormone release (Gue et al. 1989), activity and behaviour (King et al. 2003). Noise is an important stressor that affects the welfare of captive laboratory animals (Jain et al. 2003). In a forest habitat, ambient noise levels ranged from 40 – 70 dB and in savannah habitats it was 20 – 36 dB (Waser et al. 1986). However, the sound of metal on metal during cage cleaning in a laboratory was measured to be 80 dB and had a wide spectrum of harmonics that were rich in different frequencies (Morgan et al. 2007). Noise made by the capture device may compound stress experienced by the captured animal and contribute to the initial startle responses. When inspecting fox trap lines that also used Victor Soft-Catch #3 traps, treadle-snares holding foxes were heard up to 50 m away by a characteristic ‘metal against metal’ sound of the treadle plate, the chain moving through the eye of the main spring and the sound of the device hitting hard surfaces. In contrast, Victor Soft-Catch #3 traps appeared to make far less sound if they were tethered on a short chain and fox captures could not be heard until a close approach was made to the trap site (C.A. Marks, personal observations). Post-capture noise stressors could be hypothesised as a possible contributing reason why comparative blood biochemistry values for foxes trapped in treadle-snares and Victor Soft-Catch traps differed significantly.
By reducing the length of snare anchoring cables used for bears it was suggested that dehydration and muscle injury could be reduced (Cattet et al. 2003). Traps and snares can also be attached to a movable object that produces less resistance than pulling at a fixed cable and this may also permit animals to seek shelter (Kirkwood 2005), yet Englund (1982) reported that 13% of foxes held in leg-hold snares moved the drag more than 500 m from point of capture and could avoid detection. Foxes also may become tangled in snares and trap cables more easily when drags are used and this may be responsible for increased incidence of fractures and dislocations (Linhart et al. 1988; Logan et al. 1999; Powell 2005).
Fate of foxes after release
No deaths or debilitation following the release of foxes recovered by any live capture method were detected in radio-collared adult foxes (Marks and Bloomfield 2006) and cubs (Robinson and Marks 2000), which were frequently observed for up to two years. Of these, 13/20 adults had been captured by treadle-snares and no obvious diminished mobility was seen after release (C.A. Marks unpublished data) nor were injuries related to prior trapping seen upon later recovery (Marks and Bloomfield 1999b). Bubella et al. (1998) radio-collared and observed 40 red foxes that had been captured with treadle-snares in an alpine habitat. Treadle-snares had been inspected each morning and periods of captivity of up to 12 hours were likely as captures predominantly occurred at night. Recovered foxes had signs of oedema and skin abrasions, yet no deaths or debilitation, deformation of limbs or limping was observed in the two years of the study. Nine foxes that were later recaptured showed no sign of having been trapped previously (Bubella et al. 1998). Foxes appear to recover from the stress associated with treadle-snare captures for up to 12 hours and their survival does not appear to be compromised. Longer periods confined to leg-hold traps are thought to be associated with correspondingly larger exertion, struggling, injury and death (Powell et al. 2003). The level of physiological response that might be indicative of chronic debilitation in foxes after capture remains speculative.
Animal welfare implications
Scoring injuries and monitoring survival may discern relative differences in extreme welfare outcomes. However, injury and death are end-points of poor welfare and monitoring trapping stress using physiological indicators allows the relative impact of different recovery techniques to be compared and the potential for pathological states to be predicted. Treadle-snares are unlikely to produce similar welfare outcomes to the VSC #3 trap as elevated N:L ratios, CK values and profiles indicative of dehydration suggest that treadle-snares were the most stressful of the live recovery techniques used. Different pest control and wildlife management techniques might vary greatly in the magnitude and nature of stress they produce and physiological indicators may be highly informative for qualifying and ranking relative welfare states. Blood normals, especially those obtained post mortem or after restraint, are susceptible to variations caused by the collection techniques. Establishing blood normals that provide a good benchmark for free-ranging canids is an important step in developing the capacity to use physiological indicators to investigate comparative welfare states.
Acknowledgements
The analysis of these data was undertaken by Nocturnal Wildlife Research Pty Ltd as part of a contract with the Bureau of Animal Welfare (Department of Primary Industries -Victoria). Many thanks to Jane Malcolm for her support and input and to the pathologists and staff of Dorevitch Pathology who undertook the haematological and biochemistry analysis. Tim Bloomfield’s technical assistance and contribution to the original urban fox research is recognised. John Robinson assisted in the capture of many of the foxes used for blood sampling and the late-great Bill Baker allowed us to blood sample netted foxes as part of his pest control business activities, assisted by Snow I, N-----and Snow II. All research was conducted in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes and research used procedures approved by the Animal Ethics Committee of the then Department of Conservation and Environment. Dr Charles Hackman and Ms Jane Malcolm and two anonymous referees provided constructive criticism of the paper.
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Table 1. Mean haematology and blood biochemistry values with standard error (SE) and standard deviation (SD) for foxes recovered using cage traps (C), netting (N), shooting (S), treadle-snares (T) and Victor Soft-Catch #3 traps (VSC). The level of significant difference from multiple comparisons using the Least Significant Difference (LSD) test is given at two probability (P) levels.
| unit | T | n | mean | SE | SD | P | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| < 0.05 | < 0.01 | |||||||||
| Haemoglobin | Hb | g/L-1 | C | 8 | 104 | 3.7 | 10 | T | S | |
| N | 17 | 116 | 6.4 | 26 | S,T | |||||
| S | 11 | 125 | 7.4 | 25 | N | C | ||||
| T | 45 | 152 | 2.8 | 19 | C,N | |||||
| V | 7 | 135 | 4.6 | 12 | ||||||
| Neutrophil:Lymphocytes | N:L | ratio | C | 8 | 4.0 | 1.4 | 4.0 | T | ||
| N | 17 | 2.3 | 0.4 | 1.6 | T | |||||
| S | 11 | 5.4 | 2.1 | 7.0 | T | |||||
| T | 45 | 22.0 | 2.8 | 18.8 | V,C,N,S | |||||
| V | 7 | 5.9 | 1.9 | 5.0 | T | |||||
| Packed cell volume | PCV | % | C | 8 | 35.2 | 0.25 | 0.7 | N | S,T,V | |
| N | 17 | 37.3 | 1.6 | 6.6 | C,V | T | ||||
| S | 11 | 39.6 | 2.2 | 7.3 | C,T | |||||
| T | 45 | 48.9 | 0.87 | 5.8 | C,N,S | |||||
| V | 7 | 42.1 | 1.0 | 2.6 | N | C | ||||
| Red cell count | RCC | µL-1 x 10-6 | C | 8 | 8.3 | 0.31 | 0.9 | N | S,T | |
| N | 17 | 8.9 | 0.41 | 1.7 | C | T | ||||
| S | 11 | 9.0 | 0.54 | 1.8 | C,T | |||||
| T | 45 | 11.3 | 0.2 | 1.3 | S,V,C,N | |||||
| V | 7 | 10.13 | 0.24 | 0.6 | T | |||||
| White cell count | WCC | µL-1 x 10-3 | C | 8 | 9.03 | 1.5 | 4.2 | S,T | ||
| N | 17 | 6.1 | 0.9 | 3.7 | T | |||||
| S | 11 | 3.8 | 1.1 | 3.6 | T | |||||
| T | 45 | 12.3 | 0.8 | 5.4 | C,N,S,V | |||||
| V | 7 | 5.7 | 1.4 | 3.7 | T | |||||
| Albumin | ALB | g dL-1 | C | 8 | 2.6 | 0.1 | 0.3 | T | ||
| N | 17 | 2.7 | 0.1 | 0.4 | T | |||||
| S | 11 | 2.7 | 0.1 | 0.4 | V | T | ||||
| T | 45 | 3.4 | 0.7 | 0.5 | V,C,N,S | |||||
| V | 7 | 3.0 | 0.1 | 0.2 | S | T | ||||
| Chloride | Cl | mmol/L-1 | C | 8 | 109.3 | 1.4 | 4.0 | T | ||
| N | 17 | 114.3 | 0.8 | 3.3 | V | T | ||||
| S | 11 | 113.4 | 1.1 | 3.6 | ||||||
| T | 45 | 116.7 | 0.6 | 4.0 | C | N | ||||
| V | 7 | 116.0 | 2.1 | 5.6 | N | |||||
| Creatine kinase | CK | log IU/L-1 | C | 8 | 6.3 | 0.33 | 0.9 | T,V | ||
| N | 17 | 6.2 | 0.33 | 1.4 | T,V | |||||
| S | 11 | 6.3 | 0.21 | 0.7 | V,T | |||||
| T | 45 | 9.5 | 0.13 | 0.9 | C,N,S,V | |||||
| V | 7 | 7.7 | 0.76 | 2.0 | C,S,N,T | |||||
| Glucose | Gl | C | 8 | 6.0 | 0.4 | 0.7 | ||||
| N | 17 | 7.6 | 0.8 | 2.7 | ||||||
| S | 11 | 7.5 | 1.0 | 2.8 | ||||||
| T | 45 | 3.5 | 0.3 | 2.1 | C,N,S,V | |||||
| V | 7 | 6.5 | 1.6 | 3.6 | ||||||
| Potassium | K | mmol/L-1 | C | 8 | 4.7 | 0.2 | 0.6 | S | ||
| N | 17 | 4.4 | 0.1 | 0.4 | T,V | S | ||||
| S | 11 | 5.9 | 0.3 | 1.0 | S,N,T,V | |||||
| T | 45 | 4.7 | 0.1 | 0.7 | N | S | ||||
| V | 7 | 5.1 | 0.2 | 0.5 | N | T | ||||
| Protein (total) | TP | g/dL-1 | C | 8 | 5.0 | 0.2 | 0.5 | V | T | |
| N | 17 | 5.4 | 0.2 | 0.9 | T | |||||
| S | 11 | 5.3 | 0.2 | 0.7 | T | |||||
| T | 45 | 6.6 | 0.1 | 0.7 | V | C,N,S | ||||
| V | 7 | 5.9 | 0.3 | 0.7 | C,T | |||||
| Sodium | Na | mmol/L-1 | C | 8 | 139 | 1.1 | 3.1 | V,S,T | ||
| N | 17 | 141.6 | 1.0 | 4.1 | V | S,T | ||||
| S | 11 | 144.9 | 0.9 | 3.0 | T | N,C | ||||
| T | 45 | 149.0 | 0.7 | 4.7 | V | S,C,N | ||||
| V | 7 | 144.8 | 0.9 | 2.4 | C,T |
1White et al. (1991), 2Kreeger et al. (1990a), 3Benn et al. (1986), 4Kreeger (1990b)
Table 2. Published mean haematology and blood biochemistry values with standard error (SE) and standard deviation (SD) taken after red foxes were held in cage (C) or Victor Soft-Catch #1 ½ (VSC) traps for known times in hours (h) or samples taken from shot (S) foxes, captive populations (Norm) and immediately prior to surgery (PRS) and eight hours post-surgery (POS).
| Unit | Group | n | H | mean | SE | SD | ||
|---|---|---|---|---|---|---|---|---|
| Haemoglobin | Hb | g/L-1 | C1 | 10 | 8 | 136 | 7.0 | 22.1 |
| Norm3 | 30 | - | 170 | 2.6 | 14.2 | |||
| PRS4 | 20 | - | 155 | 2.0 | 8.9 | |||
| Neutrophil:Lymphocytes | N:L | ratio | C1 | 10 | 8 | 10.4 | 0.7 | 2.2 |
| S2 | 19 | - | 2.1 | 0.6 | 2.6 | |||
| VSC2 | 6 | 2 | 10.5 | 1.5 | 3.7 | |||
| VSC2 | 4 | 8 | 25.1 | 1.8 | 3.6 | |||
| Norm3 | 30 | - | 0.9 | 0.2 | 1.1 | |||
| Packed Cell Volume | PCV | % | C1 | 10 | 8 | 42.8 | 2.6 | 8.2 |
| S2 | 20 | - | 50.2 | 1.5 | 6.7 | |||
| VSC2 | 6 | - | 44.2 | 2.9 | 7.1 | |||
| VSC2 | 9 | - | 46.7 | 5.3 | 15.9 | |||
| Norm3 | 30 | - | 48.0 | 0.7 | 4.0 | |||
| PRS4 | 10 | - | 48.1 | 0.4 | 1.3 | |||
| Red cell count | RCC | µL-1 x 10-6 | C1 | 10 | 8 | 9.4 | 0.6 | 1.9 |
| S2 | 20 | - | 11.6 | 0.3 | 1.3 | |||
| VSC2 | 6 | 2 | 10.9 | 0.6 | 1.5 | |||
| VSC2 | 4 | 8 | 11.8 | 0.9 | 1.8 | |||
| Norm3 | 30 | - | 10.8 | 0.1 | 0.5 | |||
| PRS4 | 20 | - | 11.6 | 0.1 | 0.4 | |||
| White cell count | WCC | µL-1 x 10-3 | C1 | 10 | 8 | 7.1 | 1.1 | 3.5 |
| S2 | 20 | - | 3.4 | 0.4 | 1.8 | |||
| VSC2 | 6 | 2 | 4.2 | 1.0 | 2.4 | |||
| VSC2 | 4 | 8 | 7.8 | 1.9 | 3.8 | |||
| Norm3 | 30 | - | 9.3 | 0.4 | 2.2 | |||
| PSR4 | 10 | - | 7.6 | 0.6 | 1.9 | |||
| POS4 | 10 | 8 | 11.7 | 0.7 | 2.2 | |||
| Albumin | ALB | g dL-1 | C1 | 10 | 8 | 3.0 | 0.1 | 0.3 |
| S2 | 6 | - | 3.1 | 0.1 | 0.2 | |||
| VSC2 | 5 | 2 | 3.1 | 0.1 | 0.2 | |||
| VSC2 | 23 | 8 | 2.9 | 0.1 | 0.5 | |||
| Norm3 | 30 | - | 2.9 | 0.7 | 3.8 | |||
| PRS4 | 20 | - | 3.4 | 0.1 | 0.4 | |||
| Creatine kinase | CK | log IU/L-1 | C1 | 10 | 8 | 7.3 | 0.2 | 0.6 |
| S2 | 23 | - | 6.6 | 0.3 | 1.4 | |||
| VSC2 | 6 | 2 | 6.9 | 0.4 | 1.0 | |||
| VSC2 | 5 | 8 | 10.8 | 0.3 | 0.7 | |||
| Norm3 | 30 | - | 1.9 | 0.2 | 1.1 | |||
| PRS4 | 10 | - | 2.6 | 2.0 | 6.3 | |||
| POS4 | 10 | 8 | 3.6 | 2.8 | 8.9 | |||
| Glucose | Gl | Norm3 | 30 | - | 7.6 | 1.1 | ||
| Protein (total) | TP | g/dL-1 | C1 | 10 | 8 | 4.6 | 0.1 | 0.3 |
| S2 | 23 | - | 4.8 | 0.2 | 1.0 | |||
| VSC2 | 6 | 2 | 5.3 | 0.3 | 0.7 | |||
| VSC2 | 5 | 8 | 5.1 | 0.2 | 0.4 | |||
| Norm3 | 30 | - | 6.5 | 0.1 | 0.5 | |||
| PSR4 | 10 | - | 5.4 | 0.1 | 0.3 | |||
| Sodium | Na | mmol/L-1 | C1 | 10 | 8 | 150.4 | 1.4 | 4.4 |
| S2 | 23 | - | 144.4 | 2.3 | 11.0 | |||
| VSC2 | 6 | 2 | 157.3 | 1.6 | 3.9 | |||
| VSC2 | 5 | 8 | 138.6 | 4.6 | 10.3 | |||
| Norm3 | 30 | - | 156 | 0.8 | 4.4 |
1White et al. (1991), 2Kreeger et al. (1990a), 3Benn et al. (1986), 4Kreeger (1990b)
Appendix 2.0
Table 1: Steel-jawed (non-padded) trap type, size and manufacturer (Note: list is non-extensive).
DUKE TRAPS
# 1 Coil Spring
# 1 Coil Spring, Double Jaw
# 1½ Coil Spring
# 1¾ Coil Spring
# 2 Coil Spring
# 2 Coil Spring, Off-set
# 3 Coil Spring
# 3 Coil Spring, Off-set
# 1 Long Spring
# 1 Long Spring, D. Jaw
# 1 Long Spring, Guard Trap
# 11 Long Spring
# 11 Long Spring, D. Jaw
# 6 Bear Trap
# 15 Bear Trap
SLEEPY CREEK TRAPS
# 1 Long Spring
# 1½ Long Spring
# 11 Long Spring
# 11 Long Spring, Double Jaw
# 11 Long Spring, Adj. pan
# 11 Long Spring, Adj. pan, D. Jaw.
# 2 Long Spring
# 1 Coil Spring
# 1 Coil Spring, Double Jaw
# 1½ Coil Spring
# 1½ Coil Spring, Off-set
# 1¾ Coil Spring
# 1¾ Coil Spring, Off-set
MINNESOTA BRAND
MB-650 -Standard
MB-650 -Outside Laminated
MB-650 -Inside Laminated
MB-650-C -Cast Jaws
MB-750 -Beaver
MB-750 -Beaver, Laminated
MB-750 -Beaver, Off-set
MB-750 -Off-set, Laminated
MB-750-Wolf/Lion, ¼" Off-set
MB-750-Wolf/Lion, 3/8" Off-set
BRIDGER TRAPS
# 1 Long Spring
# 1 Sure Grip
# 11 Long Spring
# 5 Long Spring
# 5 Long Spring, Laminated
# 1 Coil Spring
# 1.65 Coil Spring
# 1.65 Coil Spring, Off-set
# 1.65 Coil Spring, Laminated
# 1.65 Coil Spring, Laminated, Off-set
# 2 Coil Spring
# 2 Coil Spring, Off-set
# 2 Coil Spring, Laminated
# 2 Coil Spring, Laminated, Off-set
# 3 Coil Spring
# 3 Coil Spring, Off-set
# 3 Coil Spring, Laminated, Off-set
# 3 Coil Spring, Laminated
# 5 Coil Spring, Round Jaw
# 5 Coil Spring, Round Jaw., Off-set
# 5 Coil Spring, Laminated
# 5 Coil Spring, Laminated, Off-set
BLAKE AND LAMB TRAPS
# 1 Long Spring
# 1 Long Spring
# 1½ Long Spring
# 2 Long Spring
# 2½ Long Spring
# 3 Long Spring
# 1½ Coil Spring
BUTERA TRAPS -BMI
# 1.5 Coil Spring, 2 coil
# 1.75 Coil Spring, 2 coil
# 1.75 K-9 Wolfer, 2 coil
# 1.75 4x4, Off-set
# 2 K-9 Wolfer, 4 coil
# 2 Coil Spring, 2 coil
# 3 Coil Spring
VICTOR TRAPS
# 0 Long Spring
# 1 Long Spring
# 1 VG Stoploss
# 1½ VG Stoploss
# 11 Long Spring
# 1½ Long Spring
# 2 Long Spring
# 3 Long Spring
# 3 Long Spring, Off-set
STERLING
MJ 600 Coyote Trap
# 4 Long Spring
# 1 Coil Spring, Single
# 1 Coil Spring, Double
# 1½ Coil Spring
# 1.75 Regular Coil Spring
# 1.75 Coil Spring, Off-set
# 1.75 Coil Spring, 4x4
# 2 Coil Spring, Round Jaw
# 3 Coil Spring, Round Jaw
# 3 Coil Spring, Off-set
# 3 Coil Spring, Square Jaw
JUMP TRAPS, VICTOR AND BLAKE AND LAMB
Victor # 1 Jump Trap
Victor # 1½ Jump Trap
Blake and Lamb # 3 Jump Trap
Victor # 4 Jump Trap
NORTHWOOD TRAPS
# 1 Coil Spring
# 1¾ Coil Spring, Rd J.
# 2 Coil Spring, Sq. Jaw
# 3 Coil Spring, Sq. Jaw
# 11 Long Spring
# 2½ 2 Long Spring
# 2½ Long Spring, Off-set
ALASKAN
No. 9, Off-set
F.C. TAYLOR
# 2 Coil Spring
# 4 Long Spring
# 4 long Spring Off-set
C.D.R. 7.5 Beaver Trap
Standard
Inside laminated
Outside laminated
COYOTE CUFF
# 22
# 33
MONTGOMERY TRAPS
# 1½ Round Jaw
# 1½ Dogless
# 2 Round Jaw
# 2 Dogless
# 4 Dog on, Reg. Jaw
Table 2: Padded steel-jawed trap type, size and manufacturer commonly referred to in scientific literature (Note: list is non-extensive).
| PADDED TRAPS | |
|---|---|
|
LANES LIVESTOCK PROTECTION COMPANY BRAUN BUTERA TRAPS – BMI |
JAKES (J.C. Conner) DUKE TRAPS ONEIDA VICTOR INC. LTD. |
Table 3 Leg-hold and neck snares and manufacturer commonly referred to in scientific literature (Note: list is non-extensive).
| FOOTHOLD SNARES | |
|---|---|
|
ALDRIDGE TRAP/SNARE GLENBOURN MOTORS WILDLIFE SERVICES GREEN MOUNTAIN INC E.R. STEELE PRODUCTS FREEMONT HUMANE TRAPS |
UNKNOWN MANUFACTURER RL04 trap/snare Ezyonem foot-snare Rose leg cuff L83 trap/snare Goodwin humane leg-hold trap |
Appendix 3:
Trapping practices used for canid research in Australia
The following details the devices and summarises the trapping methods reported during wildlife research studies in Australia (as discussed in Chapter 7).
Table 1. Trap type (TS = treadle snare, VSC = Victor Soft-Catch), size and modification (P = padded) for Australian research studies that have used leg-hold traps for the recovery of wild dogs (D), red foxes (F) or feral cats (C). The number of foxes captured (Nc), radio-collared (Nr), those that received major injuries due to capture (Ni), the number that exhibited abnormal behaviour after release (Nab), and mortality associated with trapping injuries subsequent to release (Nm). (NS = not stated).
| TRAP | SIZE | MOD | TS | INSPECTION | Nc | Nr | Ni | Nab | Nm | AUTHORITY |
|---|---|---|---|---|---|---|---|---|---|---|
| Lane’s | NS | D | ≈D | 95 | - | NS | - | - | Newsome et al. 1983 | |
| Oneida | #14 | D | ≈D | 51 | - | NS | - | - | Newsome et al. 1983 | |
| Lane’s | NS | D | NS | 13 | - | NS | - | - | Corbett 1974 | |
| Lane’s | NS | P | D | D | 15 | 11 | NS | 0 | 0 | Harden et al. 1985 |
| Oneida | #14 | P | D | ≈D | 9 | 9 | NS | 0 | 0 | McIlroy et al. 1986 |
| Lane’s | D/F | ≈48 | 73 | - | 23 | - | - | Stevens and Brown 1987 | ||
| TS | D/F | ≈48 | 71 | - | 4 | - | - | Stevens and Brown 1987 | ||
| Lane’s | NS | D | NS | 160 | NA | NS | - | - | Jones and Stevens 1988 | |
| Lane’s? | NS | P | F | NS | 6 | 6 | NS | NS | 0 | Phillips and Catling 1991 |
| Lane’s | NS | P | D | NS | 205 | 54 | 12 | 2 | Thomson 1992 | |
| TS | NA | F | NS | 6 | NS | 0 | 0 | Coman et al. 1991 | ||
| VSC | #3 | F | D | 28 | NA | 3 | - | - | Meek et al. 1995 | |
| TS | NA | F | D | 7 | NA | 0 | - | - | Meek et al. 1995 | |
| VSC | #3 | D | D | 11 | NA | 0 | - | - | Meek et al. 1995 | |
| TS | NA | D | D | 7 | NA | 0 | - | - | Meek et al. 1995 | |
| TS | NA | F | D | 71 | 40 | 3 | 0 | 0 | Bubella et al. 1998 | |
| TS/VSC | #3 | F | < 4 hours | 125 | - | 3 | 0 | 0 | Marks and Bloomfield (1998, 1999b) | |
| VSC | #3 | F | D | 21 | 18 | NS | 4? | Meek and Saunders 2000 | ||
| VSC | 1 1/2 | F/C | 1 | 1 | NA | - | - | Molsher 2001 | ||
| TS/VSC | #3 | F | < 4 hours | 21 | 21 | 0 | 0 | 0 | Robinson and Marks 2001 | |
| TS/VSC | #3 | D | D | 20 | 0 | 0 | 0 | 0 | Marks et al. 2004 | |
| VSC | NS | F | D | 0 | 0 | 0 | White et al. 2006 | |||
| TS/VSC | #3 | F | < 4 hours | 20 | 20 | 0 | 0 | 0 | Marks and Bloomfield 2006 |
Wild dogs
Newsome et al. (1983) used Lane’s steel traps (Stockbrands Pty Ltd: Western Australia) and lighter Oneida No. 14 steel jump-traps (Victor Oneida Co.: U.S.A.). Traps were mostly checked daily but not always if trap-lines were long, in remote and rugged country, or where access was impeded by heavy snow. Traps were set on fauna trails, forestry roads, and creek crossings, were dingoes had urinated or defecated, and where dingoes had killed livestock. Trap-sites were mostly baited with lures or carcasses to attract dingoes. Most lures included dog or dingo faeces, urine or both, and sometimes the contents of the lower intestines of trapped dingoes. Traps were set up to a metre away from main trails or wheel tracks to try to avoid catching non-target species, set with dingo scats along fire trails, ridge tops and creeks, and inspected at least daily (Harden et al. 1985). McIlroy et al. (1986) used modified Oneida No. 14 jump traps set along fire trails, at sites where dogs were likely to urinate or defecate. Each trap was attached to a steel post in the ground by a short chain and a coil spring. Jones and Stevens (1988) analysed 160 dingo carcasses that were trapped with Lane’s steel-jawed traps for their reproductive status, but no details of trapping methods, injuries or non-target captures are given. Marks et al. (2004) trapped dingoes with modified #3 Victor Soft-Catch® leg-hold traps (Woodstream Corporation, Lititz, PA, USA). Trap modifications included: #11 PIT Pan Tension Kit; #4 Montgomery coil springs; D-ring base plate; 1.2m chain containing double swivels and a #19 PIT Cushion Spring attached midway on the chain (Minnesota Trapline Company). Trap sites were lured with either a commercial canid attractant (Canine Call, Magna Glan or Final Touch: Minnesota Trapline Company) or with fermented meat preparations.
Red foxes
Phillips and Catling (1991) used steel leg-hold traps with padded jaws to capture six foxes in the southern portion of Nadgee Nature Reserve in south-eastern Australia. Foxes were radio-collared and monitored for 13-35 days. Coman et al. (1991) radio-collared six foxes after capture using treadle-snares and monitored them for up to two months. Neither of these studies record trapping injuries or non-target captures. Meek et al. (1995) used Victor Soft-Catch traps and treadle-snares to catch foxes and dogs. Traps were usually set in groups of two or three around a carcass or along roadsides and fire tracks, or were set without using lures, in the furrows made by car tyres along sandy bush tracks. All traps were checked early each morning. Lures consisted of beef pieces, road-kill macropod carcasses, fox urine and synthetic fermented egg (SFE). Treadle-snares were used by Bubela et al. (1998) in snow-covered habitat and most (81%) were set on baits -usually whole or half rabbit carcasses tethered to a stake or a bush. Whole road-killed kangaroo, wallaby, wombat and sheep carcasses were used. Snares were generally paired, and on large (kangaroo and sheep) carcasses, up to five snares were set. Baits were covered with clumps of snow grass to avoid attracting ravens. Some snares (19%) were also set on walking or animal tracks that showed signs of red fox activity. Snares were checked every morning immediately following dawn. Forty individuals were fitted with two-stage radio-transmitters and radio-tracked for an average of seven months. Marks and Bloomfield (1998, 1999b, 2006) and Robinson and Marks (2001) trapped foxes at six field sites in metropolitan Melbourne using the treadle-snare (Stevens and Brown, 1987; Meek et al., 1995) as the predominant capture device, although the #3 Victor Soft-Catch traps were occasionally used with a small number of cage traps. Traps were generally set alongside known fox trails beneath fences or gates, along culverts or outside natal dens and diurnal shelter sites. When it was necessary to position traps in relatively open areas, the trap site was baited with chicken carcasses or a fish-based cat food. Traps were inspected at least every four hours during the evening, were monitored with wireless microphones or trap monitoring transmitters (C.A. Marks, unpublished data) and covered during the day and uncovered at 2000 hrs. Radio-collars were attached to a sample of foxes and 20 individuals were tracked to obtain home range and diurnal shelter positions. Another 21 cubs were radio-collared and, of these, 14 cubs were located at, or after three months, for up to two years (Robinson and Marks 2001). Meek and Saunders (2000) trapped 21 foxes using #3 Victor Soft-Catch Traps. Kay et al. (2000) used Victor Soft-Catch size #1½ trap tethered to a 50-cm steel peg that was driven into the ground beneath the trap. The traps were set at irregular intervals along fire trails and farm roads and baited with either meat (rabbit, sheep, and kangaroo) or lure (fox urine, fox faeces, synthetic fermented egg), or both. Multiple trap sets of 2–6 traps were occasionally established around animal carcasses (sheep or kangaroo). Traps were checked for captures each morning and, if necessary, were reset each afternoon. White et al. (2006) trapped 9 foxes using Victor Soft-Catch traps (size not specified) (Woodstream Corporation, Lititz, USA), set just below ground level and tethered to a peg. The traps were set along tracks, against fallen trees and fence posts and at other locations considered suitable for capturing foxes. Trap sets were baited with chicken, beef or salami baits or anal gland or tuna oil lures, or a combination of both, set in the late afternoon and deactivated in the morning. Each fox was fitted with a radio-tracking collar after trapping and all were checked again during the evening and were watched moving throughout their home range to ensure that they had fully recovered. The ranging behaviour of foxes was determined from nine individuals. Molsher (2001) used Victor #1½ Soft-Catch traps to capture cats; trap sites were chosen to minimise capture of non-target species by setting under bushes, beside vehicle tracks, beside logs, on animal runways and at rabbit warrens. Traps were set just below ground level and tethered to a stake. They were most commonly set at the entrance to fallen hollow logs so as to provide cover for the trapped individual and also to allow the bait to be hidden from view of non-target bird species. The bait at leg-hold traps was tethered on wire (usually to the log) and positioned approximately 10–15 cm behind (i.e. furthest from the approaching cat) the plate of the trap.
References
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