Report a Bat Roost

If you have found or are aware of a bat roost here on the Central Coast, please use the form at the bottom of the page to let us know its location.

Avoiding Roost Disturbance

Please note: As with any wild animal, you should never try to pick up a bat and especially, you should not disturb bats at their roosts. Despite all good intentions, disturbing a roost is detrimental to bats. It may cause at minimum unwarranted energy expenditure, which may have detrimental physiological consequences. Consequences that are more serious may include disruption in feeding or abandonment of young or even abandonment of the roost.

Considering all of our Central Coast bats are beneficial to humans (and of tremendous benefit to sustainable agricultural practices), we hope that you will help us protect our bat populations. If you do know of a roost, please consider viewing the bats only from a distance. When you report your roost to us, we’ll use our bat detection equipment and trained monitors to determine how many and what species of bats occur at the roost.

Roost types

Possible roost sites include natural habitats such as caves, rock crevices, and trees as well as structures such as bat houses, bridges, attics, church steeples (and belfries), barns and other “out buildings”. Naturally formed, climate-stable roosts are favored in the wild; wood and concrete are favored over metal. The latter (metal) typically conducts heat in ways that are not well suited to bat use.

North American bats typically have two distinct types of roosts, day roosts and night roosts. For our non-migratory bats, a summer day roost may serve a dual purpose as an over-wintering site. Due to our mild winters here on the Central Coast, bats can be active year-round. These bats may not truly hibernate but rather maintain body temperatures low enough to minimize energy source depletion during times of inactivity (e.g., during extended periods of cool or rainy weather) but which allows them to become active when conditions are favorable for foraging (e.g., following a day or more of suitably warm weather).

Day Roosts

Day roosts are chosen to provide shelter during the day when bats are not active. Day roosts are typically reliable places of refuge that afford bat-suitable temperatures and moisture levels and, for females, a safe place to bear and sequester young as the young develop. A roost may harbor an individual bat, small groups of bats (for example, a bachelor roost inside a cavity or behind the bark of a tree), mixed colonies (where males are often separated spatially from females and young), and maternity roosts. Many day roosts have a long history of occupation and have been used by many generations of bats.

During our (northern hemisphere) summer, it is typical for male bats to roost separately from female bats. Female bats typically form maternity (day) roosts that offer safe areas to give birth and raise their young.

Night Roosts

Night roosts are typically separate from day roosts. Night roosts are typically near where bats forage, which may not be in the immediate area of the day roost . . . and bats may not use the same night roosts every night. Night roosts typically afford bats a place to take refuge specifically so that they can rest and digest following evening feeding events. They are often not as well protected or hidden as are day roosts. If the night roost is separate from the day roost, it is typical that the bats will visit for shorter period of time but during that time they will leave evidence (“sign”) of their (temporary) presence. Sign may include pellet-like guano but may also, for some species (such as the Pallid Bat) include undigested insect parts (for example, heads, legs, or other body parts of crickets and potato bugs (aka Jerusalem Cricket). 

Roost Size

Bat roosts can vary in population size. A roost may be relatively small – for example, a bachelor roost may consist of but one to only a few individuals – or very, very large! Bracken Cave outside of San Antonio, Texas harbors some 20 MILLION (or more) Mexican Free-tailed Bats. It is the largest known bat day roost in the world! Although Bracken Cave is certainly at the extreme, Carlsbad Caverns outside of Carlsbad, New Mexico and the Congress Avenue Bridge in Austin, Texas both are home to more than a million bats each.

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