Far from being pests, all species of bats found in British Columbia are voracious insect predators. Bats eat up to half their weight every night in moths, mosquitoes, beetles, crickets, grasshoppers and flies. A single little brown bat may catch up to 600 insects an hour.
There are 16 species of bats in the province and all are protected under the provincial Wildlife Act. Most species are dark brown with short ears and small bodies about the size of mice. Wingspans range from 20 to 42 centimetres (about 9 to 16 inches). The most common species found in buildings are the little brown bat (Myotis lucifugus) and big brown bat (Eptesicus fuscus), which thrive throughout the province, and the Yuma myotis (Myotis yumanensis), which is found only in the southern part of the province.
Bats enter a building for a variety of reasons, including simply flying in by accident. They may use buildings as a temporary, daytime roost, as a nursery to rear their young or, occasionally, as a hibernation site. Attics are a favorite bat refuge.
Like other mammals, bats can carry fleas, mites and ticks; in rare cases, they contract rabies. Unlike other mammals with rabies, however, they tend to get sick and die before becoming aggressive. According to Agriculture and Agri-Food Canada, which tests about 100 injured, sick or dead bats annually, no one has contracted rabies from a bat in B.C.
Social bats may roost in caves, buildings, hollow trees, animal burrows, abandoned mines and other protected areas, while solitary bats may live among leaves or under the bark of trees, rock crevices and other suitable spaces. In winter some bat species migrate to warmer climates up to 1000 miles away to feed; others hibernate in the regions of their summer roosts.
There are three general types of bat gathering places: day roosts, night roosts and hibernacula. Maturnity roost comprised of only females, may be found in; i.e. buildings or mine shafts with temperatures up to 40 degrees celsius and a high percentage of humidity to ensure rapid growth in the young. Female bats give birth to only one or two young annually and roost in small or large numbers. Males may live singly or in small groups but scientists are still unsure of the whereabouts of most males in summer.
Many bats use one or more night roosts to rest and digest food. It is also thought that night roosts may be used as locations to share information about prey availability.
Winter hibernacula are shared by both males and females of the same species and may be several hundred kilometers away from summer roosts. The largest known winter population in B.C. consisted of about 50 bats while in Eastern Canada 10 – 15,000 bats roost together. The temperature of the hibernacula is extremely important to the survival of the bats. If the temperature drops below 0 o C the bats will freeze to death or die of starvation. In too warm a place, bats will starve to death due to the rise in the metabolic rate causing the burn-up of all stored fat reserves.
An intensive inventory of potential hibernation sites in B.C. is still required. When bats roost in buildings they often get into conflict with people due to human ignorance or the noise and guano (droppings) the bats generate. Eviction and exclusion are safe and permanent solutions to the problem. Bats often choose buildings for their suitability as nurseries and can be quite persistent in trying to get in. A gap as small as 5 mm is a potential access point. To pinpoint entrances observe leaving or returning bats at dusk, and watch for scratches, stains from body oils and droppings. Screening of access points is very effective since unlike rats and squirrels bats cannot chew through wire.
The openings must not be covered during the summer (day or night) since there might be flightless young in the roost who would starve to death. The best time to permanently seal off openings and keep them from returning is late autumn or winter when bats have already migrated or left to hibernate. There is no evidence that chemicals (i.e. moth balls) or ultrasonic devices repel bats. Ultrasonic noise makers may attract bats, while mothballs (naphthalene) are toxic and dangerous to humans and pets. Other poisons may weaken the bats and could therefore increase contact between bats and humans or pets. Weakened bats may also be more susceptible to other diseases i.e. rabies. Do not use pesticides to “protect” or rid yourself from bats. Bats are protected under the BC Provincial Wildlife Act and special permits must be obtained to kill them. The chance of being “attacked” by a rabid bat is extremely rare in B.C. As a precaution avoid handling bats altogether, but should it be necessary, thick leather gloves should be worn to touch live bats and disposable plastic ones to deal with dead bats.
Eight of the 16 bat species in B.C. are currently listed as potentially endangered or threatened. Bats eat tonnes of insects per year and are therefore susceptible to poisoning by pesticides. These poisons accumulate in the fatty tissues and are released during hibernation, migration or stress and can also be passed on to nursing young. Bats also pick up toxins from roofing and insulation materials and treated wood (i.e. Lindane) and PCP (pentachloropherol). Roosts should never be treated with chemicals.
To encourage bat populations in your neighborhood but not in your attic, bat houses are a “human-friendly” solution.
Habitat loss due to clear cutting and other forestry practices is one of the major conservation concerns. Tree inhabiting bats like the Hoary Bat ( Lasiurus cinereus ), Western Red Bat ( Lasiurus blossevillii ) and the Silver-haired Bat ( Lasionycteris noctivagans ) are adversely affected. The Keen’s Long-eared Myotis ( Myotis keenii ), a rare bat restricted almost entirely to the coastal forests of B.C. is assumed to be dependent on old growth forests. All bats need clean drinking water. Pesticide use and some logging practices contaminate streams, ponds and lakes, continuing to endanger bat populations and their habitat.