| | What are bats? | Do you want to attract bats? | What problems do bats cause? | Bats and rabies | Controlling bat problems | Summary
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What Are Bats?
Alberta's bats are small, insect-eating mammals with true flight ability. All Alberta bat species are nocturnal, flying at night in search of insects they locate with an echo location system. Bats emit a series of inaudible, high- frequency sounds that bounce off flying insects and other objects in their path. The echo tells the bat the direction and distance to the object; the bat can then capture flying insects and avoid obstacles. When inactive, bats hide in dark, secluded retreats or roosts.
All nine species of Alberta's bats are migratory, living part of the year in different locations. Spring to fall is spent feeding and rearing young. In winter, they hibernate in caves, trees, buildings and other suitable sites in Alberta and elsewhere.
Do You Want To Attract Bats?
Bats in Alberta are generally beneficial because they eat insects. Some bats consume up to one-half their weight of insects per night. A typical colony of little brown bats can consume up to 50 kg of insects in one summer. Many of these insects can be harmful or at least annoying, such as mosquitoes. Consequently, you may wish to attract bats to your home or acreage.
Bats have historically inhabited natural roosting sites, such as caves, logs, crevices, cracks and holes in trees. Clearing of forests and other human activities has reduced the number of natural roosting sites for bats. Thus, some bat species have turned to roosting in buildings and other man-made structures (Figure. 1). Bats can be attracted to roosting boxes just as birds are attracted to bird houses.
Figure 1. Colony of Little Brown Bats In an Attic
Bats only live where food supplies are adequate. Most bats are found near lakes, streams, pot holes and marshy areas where insect populations are high.Ideally, bat houses should be within 0.8 km of these habitats. Those located at a greater distance have a much lower chance of being occupied by bats.
Figure 2 shows two models of bat houses. The width of the entry space is important and should not exceed 25 mm (1 in.); the ideal width is only 19 mm (% in.). All inner surfaces must be rough enough to permit bats to climb with ease. Surfaces may be abraded with a steel brush. Alternatively, a saw cut 1 mm deep every 15 mm or so creates a satisfactory surface for bats.
Place bat houses on tree trunks or buildings about 4 to 5 rn above ground, preferably where they receive sun in the morning and shade in the afternoon. Since bats are temperature sensitive, place the house at a site where it warms up quickly in the morning but does not get too hot in the afternoon. Make the house from 19 mm (3/4 in.) lumber to provide some insulation overnight. Houses can be left unpainted or they can be painted or stained either black or brown to better absorb heat in the morning.
Figure 2. European Bat Houses
What Problems Do Bats Cause?
Bats can become a nuisance when they use man- made structures rather than their normal roosts in trees, logs and caves. Many bat complaints arise from peoples' fears and not from real damage. Folklore, superstitions and the unique nature and lifestyle of bats have all contributed to the mistrust and fear of these animals. As a rule, these beliefs and fears are unfounded. However, some valid reasons for bat management can and do exist.
The little brown bat (Figure 3) and the big brown bat (Figure 4) are the most common species of bat in Alberta. They live in colonies that number from several bats to hundreds of individuals, and often inhabit buildings. Thus, the little brown and big brown bat are normally responsible for complaints from homeowners.
Most complaints occur during spring to fall when bats are active in and around buildings. Adult females select common roost sites and rear their young in suitable buildings, usually older structures close to water and woods where flying insects are plentiful. The actual roost is normally in a dark, warm and poorly ventilated area such as an attic, crawl space or wall space.
Figure 3. Little Brown Bat | 
Figure 4. Big Brown Bat |
Incessant squeaks, scratching and other bat noises in attics, walls and chimneys can be emotionally irritating. Bat droppings and urine are unsightly and can stain walls and other wooden surfaces and cause odor and health problems. Insects can be attracted to these wastes. Parasites such as ticks, mites and fleas are found on bats and may bite humans in areas where large numbers of bats congregate. Bats can also carry rabies.
Bats and Rabies
Rabies is a serious viral disease often associated with bats. However, less than 1 percent of all bats in Alberta normally carry this disease. Potential exposure to bat rabies will be prevented if bats are left alone.
Bats on the ground, resting in direct sunlight or demonstrating other abnormal behavior such as daytime flight should be avoided. Do not allow children or pets to play with bats.
Vaccinate dogs and cats against rabies. Pets that are bitten and that were not innoculated against rabies are normally quarantined or destroyed. Persons bitten by a bat are treated against rabies. Treatment is discontinued if the bat is captured and it tests free of rabies virus.
Consider all bat bites as serious and as a potential rabies exposure. Quickly and thoroughly wash all bite or scratch wounds with soap and water and seek prompt medical attention. If possible, capture the bat that has bitten a person or pet. Wear gloves to handle all suspected rabid animals. Do not damage the head because the test for rabies is done on brain tissue. Place the bat in a sealed container and deliver it to the nearest federal veterinarian for rabies analysis.
Controlling Bat Problems
Exclusion
The most effective and only permanent solution to bat nuisance problems in buildings is to "bat proof" by making the building inaccessible to bats. Often there are only a few openings used by bats to enter a building, which makes bat proofing quite easy. Some older homes, however, may have many small openings, which make excluding bats more difficult. Little brown bats can enter buildings through a 10 mm (1/8 in.) diameter space. Normal bat entry points, especially on older homes, include the following:
- under roof overhangs where wood may be warped, shrunk or rotted
- around loose vents
- through cracks under loose flashing
- at louvers, eaves or cornices
- under loose roofing or siding
- under doors and around windows
- around chimney pipes
- where wiring and water pipes enter a building
Repair and sealing of these and other potential entry points will exclude bats.
All bats should be out of a building before bat proofing begins. The best time to bat proof is in the fall when little brown bats, Alberta's most common bat species, migrate from buildings to their winter roosts. Never bat proof a building in June or July because flightless young will be trapped inside to die. The adult bats will also be reluctant to leave their young and may be trapped inside as well. Enclosed bats will suffer and die and may cause an odor problem.
Big brown bats hibernate in buildings in Alberta and may still be present in a building in the fall. However, big brown bats tend to rear their young in one place and hibernate in another location; thus, there is a good chance that most buildings with bats in the summer will be vacated in the fall.
If you cannot wait until fall to seal a building, holes should be plugged in the early evening after bats have gone to feed. But not all bats will leave at once, and some are bound to remain in the building.
To prevent the inconvenience of having to seal holes at night and to ensure that all or most bats have left a building, use a one-way device to allow bats to leave but not return. After several days, remove the devices and plug the holes.
A simple one-way device can be made using a plastic bag with the bottom cut out. Attach one end of the bag securely over an opening and allow the bag to hang loosely. Bats will drop down and out of the bag as they exit, but cannot re- enter (Figure 5).
Figure 5. Home-made Bat Valve
Be systematic and thorough when bat proofing. Seal all cracks or holes 10 mm (% in.) or larger in diameter. Make bat counts and notice where bats exit. Leave main bat exits open until last; then use a one-way valve or plug these final holes in the evening after all bats have left.
Bats do not chew wood or other building materials as rodents do. Consequently, you can use many materials such as insulation, screen, caulk, flashing, weather stripping or steel wool to exclude bats.
Many types of commercial caulking compounds and putty or oakum can be applied to cracks, holes and crevices. Spray-on foam sealants, available in an aerosol spray can, will also work well to seal cracks and crevices.
Seal spaces under doors with weather stripping to exclude bats and other nuisances. Replace or secure damaged, loose or rotted boards, siding, roofing or other materials. Install flashing where walls meet the roof or chimney and at other joints. Flashing is usually made from galvanized metal, copper, aluminum or stainless steel. A flashing called "Flashboard" is an effective material for bat proofing and has the advantages of flexibility, self-adhesiveness and convenience.
Ensure all vents are properly installed. Place screen over vents with openings 10 mm (% in.) or greater. Hardware cloth 6 mm (1/4 in.) diameter can be stapled over vents. Keep chimney dampers closed when not in use. Spark arresters or 6 mm rust-resistant bird screens should be installed on chimneys to prevent bat entry.
Fill spaces in walls and roofs used by bats with fibreglass or rock wool insulation. This also improves the building's insulative efficiency. Bats should not be present when this work is done or they will die and rot.
Repellants
Spread naphthalene crystals on the attic floor, and between walls or hang in loose mesh cloth bags from attic rafters. Use crystals in preference to "moth balls" because crystals have a large surface area and give off a stronger scent per unit volume.
Where possible, spread crystals on paper plates to make clean-up easier. Use about 2.3 kg for each 60 m3 (2000 cubic ft.) of attic space. Bats are repelled as the chemical vaporizes. However, once all the naphthalene is gone, bats usually return unless the building is bat proofed or more crystals are applied.
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Floodlights or light bulbs strung through the attic to illuminate bat roosting sites may cause bats to leave. A large attic may require 4 or more 100 watt bulbs.
Drafts from opened windows or doors can be effective to repel or discourage bats. Strong breezes created with an electric fan can also repel bats.
If a single bat is in a room, open a window or door to the outside. Turn off the lights. The bat will usually leave on its own at night.
Contact repellant glues, normally used to repel pest birds from buildings, have not proven effective to repel bats. They tend to avoid the substances or crawl over it.
Poisons
Poisons should not be used to kill bats for a number of reasons. Bats that are destroyed will usually be followed promptly by other bats. Killing bats only delays the permanent solution of bat proofing a building. The use of poison may scatter sick and dying bats to locations where children and pets may find them and be bitten. Bats stressed by sublethal doses of poison may also be more susceptible to a rabies infection that previously was latent.
Summary
No single control method is normally effective to solve wildlife problems. Bat management in and around buildings is no exception. Many factors influence what method or methods of bat management are needed.
For most situations, the exclusion of bats from buildings is the most effective, long term approach to bat management and more preferable than measures that offer short term relief of problems. Better public knowledge, understanding and tolerance is also needed to deal with bats in a practical and sensible manner.
Prepared by
Robert C. Acorn and Michael J. Dorrance, 1989
Alberta Agriculture and Rural Development
For more information
Alberta Ag-Info Centre
Call toll free: 310-FARM (3276)
Source: Agdex FS684-13. |
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