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Fri, Nov 20, 2009

Bats of Wisconsin

Wisconsin has seven species of bats, (eight if one includes the single reported sighting of the highly endangered Indiana bat.) The largest is the hoary bat, but it seldom weighs more than 11/4 oz. Stories of larger bats are likely the result of misidentified screech owls or other birds. The hoary bat, red bat and silver-haired bat live solitary lives among the trees. Their beautifully colored, silky fur blends in with their surroundings. Each fall they fly south, probably to the Gulf States, where they hibernate over winter perched in the branches of trees. They survive below freezing weather because their blood has a natural antifreeze. When warm weather returns, they fly north to spend summer in Wisconsin. Some bats have returned to the same branch of the same tree year after year to raise their young.

Wisconsin’s four other bat species winter in abandoned mines or caves locally. In summer, northern myotis hide in rock crevices, under bark or in hollow trees. Females with young may prefer heavily forested areas. Eastern Pipistrelles, our smallest bats, are sometimes mistaken for moths. They are rare near human structures, preferring instead to roost in dense foliage.

Big-brown and little-brown bats are colonial, sometimes roosting in buildings. Roosts are chosen for their nearness to large insect populations. Bats eat tremendous numbers of mosquitoes and agricultural pest insects. A little little-brown bat may eat up to 900 small insects in an hour, and average colonies may consume 500,000 insects or more each night! Such bats tend to feed near their roost to conserve energy, and many people with bat colonies report fewer mosquito problems near their homes.

Big-brown bats also have large appetites. Males often roost under eaves or shutters, away from nursery roosts to allow greater food supplies for mother bats and their young. Roosts are carefully selected for maximum infant growth and survival. As old, hollow trees are becoming harder to find, bats increasingly may have to rely on the warmth and safety of residential attics. Once a roost is established, bats remain quite loyal to it. Big-brown bats have found their way home when released in unfamiliar areas up to 250 miles away.

Nuisance Management

If a bat enters your home, don’t panic. Open a door or window to circulate fresh air, and the bat will probably find its way out within minutes. They can be chased out by waving a towel or safely picked up with heavy leather gloves or forceps. Bats causing nuisances of sound, odor or staining may be safely and permanently excluded by sealing their entrance holes after their nightly or seasonal departure.

NEVER POISON BATS. Serious health hazards will result, and other bats will reoccupy the roost once costly poisons wear off.

Older buildings may have housed bat colonies for many generations without incident. And yet, the discovery of bats in one’s attic can often cause much needless alarm. While bats and other wildlife should not be handled and should be excluded from human living quarters, the mere presence of bats in attics or garages does not constitute a public health hazard. For more information read “Bats & Public Health”, available from the Milwaukee Public Museum.

Bats of Wisconsin

Big Brown (Eptesicus fuscus)
This is one of the most widespread bats in the U.S. occurring throughout the lower 48 states, and the bat with which people are most likely to encounter. Big brown bats hibernate in caves, mines and other underground structures. While hibernating, the body temperature may be only slightly above freezing, enabling this species to be in attics or more exposed parts of caves of mines. During the summer, roost sites include attics, barns, bridges, and other man-made structures. Colonies of a few to several hundred females gather to form maternity colonies.

Silver Hair (Lasionycteris noctivagans)
Found throughout most of the United States, silver-haired bats undertake seasonal migrations. They frequently collide with radio towers and high-rise buildings during their fall migration, which is often in the company of red bats and small birds. Silver-haired bats hibernate in trees, buildings and rock crevices. Seasonal, geographic segregation of the sexes is likely in this species. In summer, males were found in southwest exclusively, females in northeast. Day roosting sites include under loose tree bark, bird nests and in woodpecker holes. They may also appear in any kind of building, but favor open sheds or garages versus closed attics.

Red Bat Red Bat (Lasiurus borealis)
Among the most abundant bats in much of Canada and the U.S. Wisconsin red bats undertake long, seasonal migrations. At such times, groups of up to 100 have been sighted.

Hoary Bat (Lasiurus cinereus)
Most widespread bat in the Americas. Found throughout the lower 48 states except for the southern half of Florida. Hoary bats make long seasonal migrations to and from warmer winter habitats in sub-tropical or tropical America. Traveling in waves, they are often found in the company of birds, who also migrate in groups. In most of their summer range and in some areas during spring migration, females and males seem to be geographically separated.

Little Brown (Myotis lucifugus)
This animal is widely distributed throughout Wisconsin and the U.S. Little brown bats usually hibernate in caves and mines, often in association with big brown bats and eastern pipistrelles. In the summer, they will often inhabit buildings, usually rather hot attics, where females form nursery colonies of hundreds or even thousands of individuals. Where males spend the summer is unknown but it is likely scattered and solitary - using a variety of roost types.

Northern Myotis (Myotis septentrionalis)
Long-eared bats are found in the eastern U.S. and throughout most of the Great Plains. They hibernate in caves in winter, where it is relatively cool and moist, and where the air is stagnant. In summer roost sites include buildings, under tree bark, and under shutters.

Eastern Pipistrelle (Pipistrellus subflavus)
The eastern pipistrelle hibernates in more caves of eastern North America than any other bat, typically choosing roosting locations where moisture condenses on its fur, giving it the appearance of a frosted Christmas ornament. Because pipistrelles are quite susceptible to freezing, they are among the first bats to begin hibernation in the fall and last to leave in spring. Despite being one of the most widespread and abundant bats of eastern North America, little is known about the eastern pipistrelle. Its summer behavior and roosting preferences remain largely unstudied.

Indiana Bat (Myotis sodalis)
Indiana bats are found in cave regions in the eastern U.S. There has been only one documented record for this species in Wisconsin. Indiana bats hibernate in dense clusters in caves. It is one of the most endangered species in North America.

BAT Conservation of Wisconsin, Inc.
http://www.batcow.org/