Bats are small flying mammals. Of the 25 species found in California, almost all are insectivores (insect eaters) that feed on vast numbers of night-flying insects, making them a critical part of the San Diego ecosystem.
In spring, females form colonies to give birth and rear young. Bat’s typically give birth to only one pup per year. Roosting sites include buildings, bridges, or other structures as well as caves or tree cavities. Adults leave roosts at night to forage for insects. Young bats develop rapidly, and most can fly within a month or two after birth but are very vulnerable until then.
Bats are excellent flyers and navigate using echolocation to capture insects in flight during the night. Because bats consume large numbers of insects, some people have installed bat houses with the idea that bats might control mosquitoes or other pest insects.
Tips to Discourage
Sometimes a colony of bats will show up at a house in the spring or fall. Often this is a migratory colony, and it will move on after a few weeks of rest. If the bats are in an area that can be tolerated, such as an outside eave, then wait a few weeks, and once the bats have left, seal the area, so they can’t return.
Bats flying inside inhabited buildings should be removed or excluded. If you suspect bats are roosting in your building, you’ll need to carefully look for signs of them. Bats can squeeze through openings as small as 1/4 inch. Return in the evening, just before dark, to observe how bats are gaining entry into a building by watching where they fly out. Exclusion is the primary way to manage bats, but you’ll want to be sure all bats have left the structure before you seal it up completely!
Most bats you discover indoors will be flying, but some might be roosting or asleep. During cool weather, their body temperature lowers called Torpor. Torpid bats might appear to be sick or dead or might bare their teeth or hiss, a defensive behavior to ward off potential predators. It often takes up to an hour or more for a torpid bat to warm enough to take flight. You can gently scrape a torpid bat into a can or box with some air holes to allow the bat to warm up in safety, then release it outside when it is dark. Never handle bats unless you are wearing leather gloves, since a frightened animal is likely to bite in self-defense.
A bat that flies into human living spaces usually is a young, lost one, and its only goal is to escape. A sudden, panicked exit by humans probably is the worst possible action, as it can cause the bat to hide, making it not only difficult to find but almost impossible to notice if it manages to find a way out on its own. The best action is to keep the flying bat in sight while closing doors to other parts of the house and isolating the mammal to a single room, where no pets or family members are present. If possible, open doors and windows to the outside, so the bat can find its own way of escape.
The best way to discourage them from coming back to a roosting spot is to attempt one of the following at night once they have left to hunt. Never disturb a roosting bat during the day.
Illuminating attic spaces and eaves with electric lights 24 hours a day might be helpful.
Cooling an attic with fans can make the temperature unsuitable for roosting, and the increased air movement also can create a less favorable roosting area.
Directing a fan at an outdoor roosting site after they have left to hunt discourages them from returning
All ultrasonic sound generators that have been tested have proven to be ineffective for repelling bats.
Although bats provide benefits by feeding on insects, they also can carry diseases to humans and other animals. You can greatly minimize the risk of disease transmission by never handling bats, and vaccinating your dogs and cats against rabies. It is very important to educate children never to touch a bat, dead or alive.
Bats have very tiny teeth and it can be difficult to feel a bite. It is important never to handle one with bare hands. You can use gloves, a towel, or a box and cardboard to contain it.
A bat on the ground does not necessarily mean it has rabies. If they are in an area where they aren’t harming anyone and pets and children aren’t likely to find them, leave them alone for an hour or two. Sometimes they’re tired from long migration flights.
If they appear to be suffering, please call for assistance.