Roosting is the behavior where bats rest, sleep, and socialize during their inactive periods, typically daylight hours. As nocturnal mammals, bats spend the night foraging and use roosts as sheltered havens to recharge and survive until their next period of activity. This biologically driven process is necessary for the survival of individual bats and their colonies. The specific characteristics of a chosen roost directly influence the bat’s ability to thrive and successfully reproduce.
Biological Necessity of Roosting
The most basic purpose of a roost is to provide protection from predators and adverse weather conditions, offering a secure, dark retreat during the day. Roosts play a central role in energy management, particularly through thermoregulation. Bats, especially smaller species, lose body heat quickly and rely on roost microclimates to conserve energy.
Many bats use torpor, a state of reduced metabolic rate and body temperature, to survive periods of food scarcity or low temperatures. The sheltered environment of a roost facilitates this process, which can extend into full hibernation in stable winter roosts, known as hibernacula. When bats cluster, they engage in social thermoregulation by huddling. This communal heat-sharing buffers the roost temperature against external fluctuations, making energy conservation efficient.
Roosts also serve social functions, acting as centers for communication, bonding, and colony cohesion. Female bats gather in specific, warm locations to form maternity colonies for raising their young. The stable temperatures within a maternity roost accelerate the development of flightless pups. These young require a warm environment to grow quickly before they can fly and forage.
Categorizing Roosting Locations
Roost selection is driven by the bat’s physiological and social needs at a particular time of year. Roosts are broadly categorized into natural sites and human-made structures, each offering different conditions. Natural roosts often include underground sites like caves and abandoned mines, which provide stable temperatures for hibernation or year-round day roosting.
Bats also commonly use above-ground natural features such as tree hollows, the space beneath peeling tree bark, and rock crevices. The narrow, sheltered space provides a protective microclimate that helps with temperature regulation. Different bat species may prefer specific natural settings, with some using tree foliage for temporary shelter.
Human-made structures mimic natural features and are categorized by function and duration of use. Day roosts are sites used for resting during the inactive period, such as an attic or barn, and may house maternity colonies during the summer. Night roosts are temporary, used between foraging bouts for digestion or short rests, and can include porch ceilings, open sheds, or the underside of bridges.
Recognizing and Addressing Roosts in Structures
Identifying a roost requires homeowners to look for specific signs that indicate bat presence. The most conclusive evidence is the accumulation of guano (bat feces), typically found beneath the entry point or main roosting spot. Unlike mouse droppings, bat guano crumbles easily into dust when touched because it is composed of insect exoskeletons, and it often forms large, concentrated piles.
Visual inspection may also reveal dark, greasy stains around small cracks and openings where bats squeeze in and out, caused by the oils in their fur. Homeowners may hear scratching, chirping, or squeaking sounds coming from the walls, attic, or soffits, particularly around dusk and dawn. The most definitive way to confirm a roost is to watch the structure at sunset to observe bats exiting the building.
Addressing a confirmed roost requires non-lethal exclusion, which is the only legal method for removal. Exclusion involves installing a one-way device over the entry point that allows bats to leave the structure but prevents re-entry. Attempting exclusion during the maternity season, typically early spring through mid-August, is illegal in many jurisdictions.
Excluding bats during this period risks trapping flightless young inside, where they will die, creating odor and health risks. Exclusion work must be timed to occur outside of this season, usually in the fall or early spring. This ensures that all bats, including the young, are able to fly out and find an alternative roost. Due to the need for precise timing and legal adherence, seeking assistance from a professional wildlife control specialist experienced in bat exclusion is recommended.