Bats are a diverse order of mammals, known scientifically as Chiroptera. Their habitat selection demonstrates remarkable adaptability, ranging from undisturbed wilderness to heavily modified urban landscapes. Bats are found on every continent except Antarctica, utilizing a variety of roosting sites that offer specific microclimates and protection from predators.
The Diversity of Natural Roosting Sites
Caves and abandoned mines provide stable natural roosting sites for bats. These subterranean environments offer a consistent microclimate, which is particularly suitable for large colonies and species that require stable temperatures. Abandoned mines are ecologically similar to natural caves, often providing the same dark, sheltered conditions needed for survival.
Many bat species rely on trees for shelter, utilizing both living and dead wood. They seek out tree hollows, cavities created by woodpeckers, or natural decay features within the trunk and branches. Other species prefer to roost under loose, peeling bark, often found on dead trees or species like the shagbark hickory.
Other bats choose to hang directly among the dense leaves of trees, known as “foliage-roosting bats.” Rock formations also offer habitat, with some species using narrow crevices and cracks in cliffs or rock outcrops. These rock crevices, particularly those on south-facing aspects, provide protection and stable, warm microclimates.
Habitats Provided by Human Structures
As natural habitats have been altered, bats have adapted to utilize environments created by human construction. Residential and commercial buildings are frequently used, with bats seeking shelter in attics, wall voids, and behind fascia boards or eaves. They are able to enter these structures through very small openings, sometimes gaps as small as \(1/4\) inch by \(1 1/2\) inches, which they access along rooflines or vents.
Wall voids are often preferred over attics during the summer, as the enclosed spaces between wall studs offer a more stable, less extreme temperature than attics, which can become lethally hot. Civil engineering projects also provide extensive roosting habitat for numerous species. Bridges are commonly used, with bats clustering in expansion joints, crevices, and the protected spaces between concrete girders.
Culverts, including concrete box and pipe designs, are also utilized, sometimes serving as maternity roosts in urbanized areas. Conservation efforts include the construction of purpose-built structures like bat houses or bat towers. These artificial shelters are designed to mimic natural tree cavities or crevices, and their effectiveness depends on specific design features that ensure appropriate, stable temperatures.
Seasonal and Specialized Habitat Requirements
A bat’s habitat selection is not permanent but changes throughout the year to meet specific physiological and reproductive needs. During colder periods, bats seek out hibernation roosts, known as hibernacula, which are characterized by cool, stable temperatures typically ranging from \(37\) to \(50^\circ\)F (\(3\) to \(10^\circ\)C). This microclimate, often found deep within caves, mines, or rock crevices, allows the bats to enter a state of torpor, significantly reducing their metabolic rate to survive on stored fat reserves.
In the warmer months, female bats congregate in specialized maternity roosts to give birth and raise their young. These nursery sites require significantly higher temperatures, often maintained between \(77\) and \(104^\circ\)F (\(25\) and \(40^\circ\)C), to accelerate the growth and development of the pups. The warmer temperatures reduce the energetic burden on the mother and are a major factor in selecting sun-exposed sites like attics or tree hollows with high solar gain.
Bats also use temporary night roosts during their nightly foraging excursions. These are distinct from primary day roosts and function as safe places to rest or digest a meal between feeding bouts. Night roosts are usually located close to foraging grounds and can include porches, open barns, or protected areas under bridges, allowing the bat to conserve energy before returning to the day roost before sunrise.