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Problems caused by predatory birds | FF0031 |
Ian Temby, Flora and Fauna Branch
June, 2003 |  |
Problem 1
Predation upon lambs and kids.
Problem 2
Predation upon homing or racing pigeons. Predation or attempted predation on fowls and cage birds; in the latter case, often causing death or injury to panic-stricken birds that fly into the sides of the cage.
Background
The Wedge-tailed Eagle, the Australian Raven and the Little Raven are frequently blamed for losses of young lambs and kids.
The Wedge-tailed Eagle occurs throughout Victoria where there are wooded farmlands with large trees. A study of its diet conducted near Melbourne revealed that rabbits comprised 49% of its food. This conclusion is consistent with the findings of five other studies of the diet of this species around Australia. In the study near Melbourne, adult sheep and lambs comprised 2% of the diet, somewhat less than was found in two studies in parts of southeastern Australia and in Western Australia (7% in each case). However, in the Western Australian study, it was estimated that 50% of the sheep taken were carrion.
In general, then, Wedge-tailed Eagles are not an important predator of sheep (or goats). However, there are occasions when there is a spate of predation on lambs or kids on one property, or over a small area, which can cause economic loss, particularly if stud stock are involved. If the eagle taking stock is one of an established, breeding pair and it can be trapped, holding it in captivity for two days is likely to ensure that its place is taken by another bird. It is then unlikely to be able to re-establish itself in the same area after being released.
If the Rabbit Calicivirus, combined with conventional rabbit controls, is effective in greatly reducing rabbit numbers, then Wedge-tailed Eagles may turn to lambs and goat kids as alternative food, in some cases. Where this is happening, there appear to be few options but to apply for an Authority to Control Wildlife to enable the destruction of these birds. Each application will be assessed individually by DSE.
The Australian Raven and the Little Raven are widespread throughout Victoria and are present in all farming areas. The closely related Little Crow is uncommon in Victoria and is only found in the north west corner of the State. The Forest Raven is found mainly in coastal areas. All of the ravens and the Little Crow are protected wildlife. While there are undoubtedly instances where ravens do cause substantial losses of livestock, this is the exception, rather than the rule. Detailed studies of lamb predation in Australia have shown that neither disease nor predation is responsible for most of the ten million or so deaths of newborn lambs that occur in Australia each year: most lambs die because they are starving, after the suckling relationship between mother and offspring has been broken or failed to establish. Since starvation of lambs in Australia is usually irreversible, for economic reasons, it is academic whether a predator hastens the inevitable death of such lambs. However, such starvation can be avoided. Correct nutrition of the ewe during pregnancy and the provision of adequate shelter and supervision near lambing time will reduce the number of lambs vulnerable to predation. To achieve these changes, it is necessary to accept that losses due to predation are not as large as they appear to be. The autopsy of dead lambs, the recognition of the wounds found, and the assessment of lamb viability provide logical and convincing evidence.
The Peregrine Falcon and the Brown Goshawk both feed principally on birds, although the Brown Goshawk will take rabbits readily. The Peregrine Falcon is a large, powerful falcon that feeds upon birds up to the size of galahs and ducks, usually catching them in flight. It does take pigeons and is sometimes shot or trapped illegally by pigeon fanciers for this reason. The Brown Goshawk, on the other hand, generally ambushes its prey from cover, and will follow pigeons into the pigeon coop, but seldom catches them in open flight. Both of these birds are native species and are protected under the Wildlife Act 1975.
Peregrine Falcons are threatened by the accumulation of organochlorine pesticides from the tissues of their prey. This problem, combined with habitat loss, illegal shooting, illegal capture and nest robbing, have led to drastic declines of many peregrine populations around the world. Some sub-species have become extinct. In peregrines from agricultural areas of Victoria, as a result of pesticide build-up, egg-shell thickness had declined to the critical level of 20% of normal thickness by 1984 when monitoring ceased. Any further egg-shell thinning would lead to breakages as the eggs are being incubated, and a resultant cessation of recruitment to the population.
Under no circumstances will an Authority to Control Wildlife be issued for this species.
Attacks from goshawks are most frequent during February and March, when the juveniles are dispersing. Banding and relocation of offending birds has shown that while juvenile birds are seldom recorded again after being relocated, some adult goshawks (with established territories) will return from considerable distances when relocated. Although these birds are often readily trapped and can therefore be relocated with little difficulty, this is only a short-term remedy and further attacks may occur, unless some form of exclusion is provided.
Solutions
- Consider the benefits of having these birds on the property, since ravens feed on cockchafers and other pest insects including the larvae of blowflies, and eagles and goshawks can be important in controlling rabbit numbers.
- Practice good husbandry: remove carcasses so that predators and scavengers are not attracted to the property.
- Provide adequate shelter and nutrition for ewes before lambing.
- Identify the cause of death of lambs or kids and assess their viability prior to death. View this PDF file for further information on lamb mortality and predation.
- Assess losses to these birds in the context of overall losses from all causes and judge whether further action is warranted.
- Apply for an Authority to Control Wildlife to permit destruction of a number of ravens. Applications can be obtained from the DSE Customer Service Centre on 136 186.
- Accept predation by peregrines as a natural hazard of keeping and flying pigeons and damage by goshawks as a trade-off for the benefit of their pest control activities.
- Exclude goshawks by making an outer, mesh-covered framework over an aviary, or a roofed fowl run to confine fowls.
- Exercise the birds (pigeons or fowls) between about 10 am and 4 pm, since goshawks and falcons usually hunt in the early morning and late afternoon, and are likely to have fed by 10 am, and vary the exercise time of the birds, so that birds of prey cannot learn to anticipate when birds are let out.
- Avoid flight routes which pass known peregrine territories, or where former predation problems have been encountered and vary the times and places where birds are released.
- Breed pigeons of similar colour, preferably close to natural colour, since birds of prey select odd-coloured birds out of a flock.
- In some circumstances, DSE staff may trap and relocate goshawks as a short-term remedy.
- Scare goshawks using Bird Frite cartridges. Note that the use of Bird-Frite cartridges may not be acceptable in built-up areas. Prior clearance from local Police and municipal authorities should be obtained before these devices are used in such situations.
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The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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