Cave Bats

A western small-footed myotis (Myotis ciliolabrum) launched into flight.
Photo: Michael Durham / Minden Pictures

Of the 47 bat species in North America, 18 rely heavily on caves during the year, including 13 species that live in subterranean habitat year-round. Five species depend on caves and underground habitat for hibernation.

But not all caves, cliff crevices, abandoned mines or underground spaces provide adequate habitat for bats; in fact, most do not, due to unsuitable temperature and humidity levels, exposure to light, disturbance by humans and predators, and distance from food and water resources. That means that there are relatively few subterranean spaces that many species of bats rely on, so identifying these places and protecting them are critical for their continued survival.

Who’s Living in Caves?

A male Townsend's big-eared bat (Corynorhinus townsendii)
roosts on a rock.
Photo: Michael Durham / Minden Pictures.

In the eyes of bats, not all caves are equal. And the reasons they use the underground differ depending on the species and time of year.

Caves and mines can serve as daytime roosts, where bats like the western small-footed myotis (Myotis ciliolabrum) sleeps during daylight hours; or as night roosts, where some species will head to rest and digest between nighttime foraging sessions, such as Townsend’s big-eared bat (Corynorhinus townsendii).

Bats seek out subterranean habitat for hibernation, sometimes individually, and sometimes in huge groups, like the little brown bat (Myotis lucifugus), which can congregate in the hundreds of thousands for winter hibernation. These hibernacula can also host mixed groups of different bat species, like the northern long-eared bat (Myotis septentrionalis). Unfortunately, this also enables easier transmission of the fungal pathogen that causes White-nose Syndrome, a deadly disease that has been wiping out little browns in the East and has been documented on at least six other species of cave-reliant bats.

In the summer, caves also often serve as sites for maternity roosts. The 20 million Mexican free-tailed (Tadarida brasiliensis) bats roosting in Texas’s Bracken Cave from March through October go there for a safe, warm environment in which to birth their pups. Over 500 pups per square foot have been observed crowding parts of the cave’s ceiling, huddling together for warmth and protection.

A gray myotis (Myotis grisescens) perches on a cave wall.
Photo:MerlinTuttle.org

The endangered gray bat (Myotis grisescens) of the southeastern U.S. relies on caves for hibernating, breeding and summer roosting. This species uses them as dispersal and stopover sites during migration.

Underground spaces are also known to be important places for social and mating interactions between males and females, or juveniles and adults. Indiana bats (Myotis sodalis) will swarm, or fly in and out of cave entrances throughout the night without roosting there, a behavior linked with mating encounters. It may also serve as a way for young bats to learn the location of hibernation sites.

Even some tree-roosting bats, like Utah’s western red bat (Lasiurus blossevillii) have been found roosting in caves and mines on occasion and silver haired bats (Lasionycteris noctivagans) have been observed, by BCI's SubT team, hibernating in abandoned uranium mines in both Colorado and Utah.