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Insectivorous Bats | FF0023 |
Ian Temby, Flora and Fauna Branch
September, 2003 |  |
Problem
These native mammals may roost in ceiling or wall cavities and create noises, smell and, sometimes, leave droppings inside the building. Occasionally, bats that roost in the ceiling cavity may mistakenly enter the living area in a house, through a gap in the ceiling. This can alarm some people.
Background
Most of the 20-plus species of small, insect-eating bats that occur in Victoria roost in hollows in trees. Cavities in buildings are equally acceptable roost sites for a number of these species. In some instances, there are few trees remaining that contain suitable hollows in the vicinity of a bat-tenanted building, and elimination of access to that roost site may remove a remnant bat population from an area. The retention of natural hollows in both living and dead trees is extremely important, both for bats and other wildlife.
A newly-described lyssavirus capable of causing death in humans has been isolated from four flying-fox and two insectivorous bat species. At this stage, it is not known how widespread the virus may be in bat populations. People are at little or no risk from this virus if they do not handle bats, since it is only transmitted in saliva of infected animals.
Bats in the ceiling or walls are not necessarily a problem. For example, there is little risk of disease being transmitted by bats. Bats are only likely to enter the interior of the house by mistake, and this problem can be solved by blocking any gaps between the interior and the ceiling or wall cavities. Bats do not become tangled in people’s hair; or attack and bite people. Bats are an important predator of many kinds of insects, including mosquitoes.
Removal should only be done during the bats' active season, from September to late April, but should not be undertaken during the breeding season (November through January), because dependent, non-flying young are likely to be in the roost at this time. Bats will use artificial roost boxes, and many people are happy to provide the bats with an alternative roost site near their house, before excluding them from the house.
Bats are sometimes mistaken for mice in the ceiling, and vice versa, because of the squeaking noises both make at times. Each has characteristic droppings. Bat droppings are 5-10 mm long, irregular, usually contain obvious insect remains and when dry can be crushed readily between the fingers, while dry mouse droppings tend to roll and remain intact under moderate pressure.
All native birds, mammals, amphibians and reptiles, and some introduced species such as deer, are protected under the Wildlife Act 1975, and may not be captured or harmed in any way without an authority issued under the Wildlife Act.
Solution
Prevent entry of bats from the ceiling or wall spaces to the inside of the building by sealing all gaps which lead to the ceiling or wall spaces, using cloth, paper or any other material, since bats will not remove this. Gaps can also be sealed with expanding foam or corrugated closure strips available from hardware stores. Provide alternative roost sites by constructing and placing bat houses in nearby trees, before excluding bats from the house. Identify exit points by watching at dusk to see where bats emerge from the building. A close inspection of possible exit points is often worthwhile, since there is usually some staining around frequently used routes, and there may also be droppings stuck to the surrounding area, or on the ground below. Exclude bats by sealing all entry/exit points except one. This remaining exit point can then be modified to prevent bats from re-entering, but still allow bats to leave the building. This is accomplished by creating a smooth vertical surface around the exit point which will not allow the bats to grip and climb back into the building. A refinement of this method is to attach a flap of plastic sheet to hang down over the exit point, allowing bats to leave but not to re-enter (see drawing below).
Bat Exclusion Flap
Bat roosting box
Timber for the bat box should be 19-25 mm rough sawn. Internal Height: 300 mm. Width: 100-200 mm. Entrance: 15-20 mm wide and at least 50 mm long. Roughen internal surfaces with horizontal saw cuts.
Place on tree, clear of branches or on wall of house, under eave, 2.5-3.0 m or more above ground.
Further information
See also Land for Wildlife Note No. LW0012, Bats in rural Victoria, on the DSE website.
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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