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When bats wake up too early

A bat recently brought to Wildwoods. (Photo by Megan Stanton)

Normally bats would still be in hibernation at this time of year, but sustained warm weather has disrupted their internal clocks. Three little brown bats who all woke up a bit too soon were recently admitted to Wildwoods.

There are seven species of bats in Minnesota and all but three hibernate. The hoary bat, eastern red bat and silver-haired bat all migrate south for the winter where they can find plenty of food to eat. The other four species — the tri-colored bat, big brown bat, little brown bat and northern myotis bat — find caves or mines in which to hibernate. In northern climates like ours, hibernation for bats usually begins in September and goes through May. During hibernation a bat’s heart rate will drop from a resting average of 200-300 beats per minute to just 25 beats per minute and may only take one breath a minute. Its body temperature can drop to near-freezing. All of this means a bat will use 98 percent less energy than usual.

This is called “torpor” and a bat can survive for about a month in this state. After that the bat will experience a brief period where its body temperature will rise to normal for a few hours and it may stir. Then it will return to a state of torpor and repeat the cycle for up to six months.

It may seem that bats and other animals hibernate because it is getting cold, but the cold is just an indicator that resources are scarce. Hibernation is a reaction to limited food supplies and warmer weather heralds the return of insects and other food sources. When we have sustained warm spells, like we did just a couple of weeks ago, a bat’s system can be tricked into thinking that food is available so it’s time to fully wake up. All the bat’s systems return to normal and it must find food to meet the increased energy demand. Bats who wake too early will not be able to find enough food to sustain them or restore depleted energy.

At this point in the season bats have burned through most of their energy stores (fat) and won’t survive going back into hibernation. They’ll need the intervention of licensed wildlife rehabilitators to keep them fed until they can be released in the spring.

Bats are very difficult to take care of in a wildlife rehabilitation facility. Training them to eat from a dish, and that a mealworm is an acceptable source of food, is a painstakingly slow process for us and not fun nor stress-free for the bats. We would obviously prefer that bats be allowed to stay right where they are during winter hibernation. It’s safest for them, safest for us and allows us to focus our attention more fully on the other critical patients in our care. If you have found hibernating bats in your home, we implore you to allow them to stay through the winter. They’ll be easier to evict in the spring and they will have a better chance for survival.

If you find an awakened bat on the ground or in your home, don’t panic. Your first thought will likely be, “rabid bat!” If it begins to fly around I’m guessing your next thought will be, “it’s going to get tangled in my hair and bite me!” These are both quite unlikely. Less than 1 percent of bats have rabies and the rate of transmission between bats and humans is nearly nonexistent. Bats are also, contrary to popular belief, not blind and because they can see you just fine and are so agile, they will adeptly avoid your hair. So remain calm if you happen to find a bat who has awakened too early, keep kids and pets clear of the area, and call us immediately. We will guide you safely through the process of catching the bat, or can give you the phone number of a humane animal control professional.

Wildwoods is a 501(c)(3) wildlife rehabilitation organization in Duluth. For information on how you can help wildlife, including volunteer opportunities, visit wildwoodsrehab.org, call (218) 491-3604 or write to P.O. Box 3161, Duluth, MN 55803.

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