Bats are a remarkably diverse group of mammals, found across the globe. The place a bat chooses to stay during the day, or for extended periods, is called a roost, which serves as a safe place to rest, hide from predators, and raise young. Bats spend over half their lives roosting, making the selection of these sites a fundamental aspect of their survival.
Primary Natural Habitats
Many bat species rely on natural geological and arboreal features for shelter, with caves and mines being the most widely recognized natural roosts. Caves provide a stable microclimate, which is particularly important for species that hibernate, as they need temperatures that remain consistently above freezing. Large cave systems can host massive colonies, such as the Mexican free-tailed bats in Texas, which aggregate in the millions.
Beyond underground environments, trees provide shelter for more than half of the bat species in North America. These tree-roosting bats often seek out snags (dead or dying trees), using cavities or crevices formed by damage or decay. Loose, peeling bark offers temporary, protected spaces for some species to rest or escape inclement weather.
Some bats also utilize rock crevices and dense foliage as primary natural shelters. Rock faces and cliff crevices offer narrow, protected spaces that mimic the security of a cave. Foliage-roosting bats, such as the Eastern red bat, often choose the leaves of large-crowned trees, sometimes using camouflage coloration to blend in with their surroundings.
Structures Bats Utilize
As natural habitats have been lost, many bat species have adapted to using human-built structures. Buildings, especially attics and wall voids, provide thermally stable environments that are dark and undisturbed, offering conditions similar to natural roosts. Attics are particularly popular because they trap rising heat, which is a desirable feature for female bats raising their young.
Transportation infrastructure like bridges and culverts has also become an important habitat for numerous species. Many species prefer concrete structures, which provide thermal advantages and frictional surfaces that make hanging easier. Bridges often contain vertical crevices, between 0.5 and 1.5 inches wide, effectively mimicking the natural cracks found in rocks and trees.
Farm buildings, such as old barns, are frequently used, providing large, sheltered spaces for colonies. These structures often have easy access points and offer a dark environment that protects bats during the day. Other built environments, including abandoned mines and wells, are also readily adopted for hibernation, as they replicate the cool, stable conditions of natural caves.
Roosting Sites Based on Function
The choice of a roost changes depending on the bat’s behavioral and physiological needs throughout the day and year. Day roosts are used for extended rest periods after a night of foraging, offering maximum protection from light, predators, and weather. Night roosts are temporary shelters used during the feeding period for short breaks, digestion, or social interaction, and are often less sheltered than day roosts.
Maternity roosts are selected by female bats during the summer to give birth and raise their pups. These sites require a warm, stable microclimate, ideally between 25°C and 40°C, because the young bats cannot regulate their own body temperature immediately. The elevated temperature allows the pups to grow quickly, and females will return to the same location year after year if conditions are favorable.
In colder climates, bats enter a state of deep sleep known as torpor, requiring specialized hibernation roosts, or hibernacula, during winter. These sites must maintain a temperature that is consistently low but remains above freezing, typically between 0°C and 11°C. High humidity is also required to prevent dehydration. This stable environment allows the bat to conserve energy reserves until insect prey becomes available again in the spring.