Bats in the Winter
With few flying insects available to them during winter in Washington, bats survive by hibernating, migrating to regions where insects are available, or a combination of these strategies. During hibernation, metabolic activities are greatly reduced—a bat's normal body temperature of around 100 degrees F is reduced to just one or two degrees higher than that of the hibernaculum, and their heart rate slows to only one beat every four or five seconds. A hibernating bat can thus survive on only a few grams of stored fat during the five- to six-month hibernation period.
Banding studies indicate that little brown bats will migrate 120 miles between hibernacula and summer roosts, and, if undisturbed, they occupy the same site year after year. They select areas in the hibernaculum where there is high humidity (70–95 percent), and the temperature is 34 to 41 degrees F. Still, there are some species, such as the big brown bat, that can hibernate in relatively exposed situations in buildings where there is considerable fluctuation in temperature. Hibernation lasts until April or early May, but in coastal regions bats may arouse in late winter—little brown bats have been found feeding in the Puget Sound region in mid-March.
It is important not to disturb hibernating bats. If a bat rouses early from hibernation, it must use its fat reserves to increase its body temperature. A single disturbance probably costs a bat as much energy as it would normally expend in two to three weeks hibernating. Thus, if disturbed multiple times, hibernating bats may starve to death before spring.
It is important not to disturb roosting bats at any time of the year. In the spring, disturbing a maternity colony when flightless young are present may cause young bats to be dropped to their deaths, or abandoned, by panicked females. Because some bats hibernate in buildings during the winter months, batproof a building only when you are sure no bats are hibernating in it. If bats are found hibernating inside after October 15, they should be left alone until early spring (prior to the birthing period in May) after the weather has warmed enough for insects to be out regularly. Meanwhile, seal all potential entry points into human living spaces, and develop a plan so the exclusion process can be accomplished effectively in spring
Banding studies indicate that little brown bats will migrate 120 miles between hibernacula and summer roosts, and, if undisturbed, they occupy the same site year after year. They select areas in the hibernaculum where there is high humidity (70–95 percent), and the temperature is 34 to 41 degrees F. Still, there are some species, such as the big brown bat, that can hibernate in relatively exposed situations in buildings where there is considerable fluctuation in temperature. Hibernation lasts until April or early May, but in coastal regions bats may arouse in late winter—little brown bats have been found feeding in the Puget Sound region in mid-March.
It is important not to disturb hibernating bats. If a bat rouses early from hibernation, it must use its fat reserves to increase its body temperature. A single disturbance probably costs a bat as much energy as it would normally expend in two to three weeks hibernating. Thus, if disturbed multiple times, hibernating bats may starve to death before spring.
It is important not to disturb roosting bats at any time of the year. In the spring, disturbing a maternity colony when flightless young are present may cause young bats to be dropped to their deaths, or abandoned, by panicked females. Because some bats hibernate in buildings during the winter months, batproof a building only when you are sure no bats are hibernating in it. If bats are found hibernating inside after October 15, they should be left alone until early spring (prior to the birthing period in May) after the weather has warmed enough for insects to be out regularly. Meanwhile, seal all potential entry points into human living spaces, and develop a plan so the exclusion process can be accomplished effectively in spring
This information was provided by the Washington State Department of Fish and Wildlife, Russell Link, and Michael Holmquist
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