Time for Bats to Hang It Up

Submitted by: Margie Klein (Conservation Educator, NDOW)

Now that Halloween is over, bats can retire from their nightly activities for the winter. Actually, it has nothing to do with Halloween. It’s simply that time of the year when dipping temperatures urge bats to leave their warm weather roosts and look for shelter in places like caves or abandoned mines. In southern Nevada, bats are just starting the trek into caves and other dark spaces. In northern Nevada, they are already there.

Why do bats hibernate? Bats are mammals, more closely related to primates than to rodents, and like a lot of mammals they cease to be active when winter’s chill sets in. Nevada bats hibernate mainly because their primary food source, insects, are not readily available. However, not all bats hibernate. The Brazilian free-tailed bat, for example, goes farther south for the winter. But most of Nevada’s 23 bat species do hibernate. Still, a good chill is important when they are looking for the suitable place to “hang it up” for the winter. A chilly place is important to maintain their metabolism at a low level while they sleep.

Bats may hang out in caves or abandoned mine shafts and adits (passageways). Different species have different preferences. The temperature within a cave or mine will further determine a bat’s hang-up site – some species look for the coldest area. Whatever the level of cold, it needs to be consistent. Although cliffs and crevices do not provide enough shelter for hibernation in northern Nevada, there is evidence that they are used by Mojave Desert species during the winter.

Bats can lower their body temperature almost to freezing, but blood does not freeze at this temperature. Their hearts may beat only 10 times a minute, compared to a thousand times per minute when fully awake. This way, they use up very little energy. This state of inactivity is called “torpor.” This means that they can awake from the sleep state briefly. And some species, such as the pallid bat, do just that, in order to feed and drink. Because so much energy is used up in their small bodies while they sleep, they may have to re-energize by supplementing their fat reserves.

Ever wonder where a bat stores fat? It’s deposited between their shoulders. While they do exhibit intense night feeding before hibernation, sometimes it’s not enough. Bats can lose up to half their body weight during hibernation. If they awake due to no impulse of their own, the disturbance can be highly detrimental to them. In fact, disturbing sleeping bats can lead to their starvation as they unnecessarily burn up their reserves.

“It’s best not to disturb hibernating colonies at all. The best way to avoid waking them is to stay out of caves and mines where bats might be roosting for the winter,” said Tracy Kipke, a habitat biologist for the Nevada Department of Wildlife.

It’s especially important that we respect bats, as they are beneficial to the environment and help to reduce the number of pesky insects. We also have to respect them because many of them are in trouble, mostly due to loss of habitat, said Kipke. The spotted bat is threatened in Nevada, and a number of species are protected as well. That list includes the pallid, Allen’s lappet-eared, and Brazilian free-tailed bats. Several bats are also listed as sensitive species. These include the California leaf-nosed, Western red, Townsend’s big-eared, and Western mastiff bats.

Once winter is over, when can we expect these furry little creatures to appear again? They come out in March and April, when the females congregate and maternity season follows. That time of year can be great for bat-watching, a time to witness large numbers of bats lifting off for the warm night skies. It would be a great addition to your star-watching activities. Remember the saying, “Abandoned mines – stay out, stay alive,” and bats will be able to as well.

The Nevada Department of Wildlife (NDOW) protects, restores and manages fish and wildlife, promotes fishing, hunting, and boating safety. NDOW’s wildlife and habitat conservation efforts are primarily funded by sportsmen’s license and conservation fees and a Federal surcharge on hunting and fishing gear. Support wildlife and habitat conservation in Nevada by purchasing a hunting, fishing, or combination license. For more information, visit www.ndow.org.