San Diego Natural History Museum--Your Nature Connection[BRCC San Diego Natural History Museum: Herpetology Department]
Birds and Mammals

Bird Atlas
The Collection
FAQ's About Birds
FAQ's About Mammals

Field Guide

Have you ever seen a bat whisk by you in the dark? Have you ever heard one echolocating by clicking or squeaking as it flies around you?

[photo of Mexican Long-Tongued Bat (Choeronycteris mexicana) hanging from beam. Photo by John Mitchell]Many people wonder what a bat is. Bats are not birds, but are mammals that are capable of flight. They do not have feathers. Instead, very thin layers of skin within their wings allow them to fly with incredible dexterity. Their ability to rapidly change directions in flight enables them to capture the most elusive insects.

Are they flying rodents?
No, they have too many differences that place them into their own taxonomic order, Chiroptera, which in Latin translates to "hand wing."

Most bats are insectivorous -- that is, they eat insects -- though some bats consume fruit, nectar, blood, fish, frogs, and other meaty prey. In San Diego County we have only insectivorous and nectivorous bats.

All San Diego County bats use echolocation to locate and capture their prey either in flight, off a tree limb, off the ground, etc. Echolocation is high frequency sound waves that are emitted through the mouth or nose of a bat which bounce off objects and return to their highly sensitive ears. This allows a bat to discern what its surroundings are (trees, walls, rocks, etc.) as well as what's alive and moving within its environment (flying insects, terrestrial insects, arboreal insects). Most bat echolocation is so fine-tuned that bats can determine exactly what type of insect they are going to capture in pure dark conditions. With this ability a single bat may capture and consume up to 500 or even 1,000 insects in one hour.

When are bats usually seen?
The majority of our bats come out of their day roosts at dusk and immediately begin searching for food. This will continue for several hours until they are satiated. The bats will then either return to their day roosts or will find places near their foraging areas to roost (called night roosts). Night roosts are often within or under bridges. Bats will roost individually or with other bats; this is often considered a social gathering. They will usually remain until dawn and forage again before returning to their day roosts where they will sleep. Day roosts can be in rock crevices, cave, buildings, hollowed tree trunks, and cracks under tree bark, etc.

Bats were once very common, but now populations are in great decline.
Partly this is due to an irrational fear of bats. Common misconceptions are that bats will pursue and bite animals, become entangled in one's hair, and that they all carry rabies. In California there is a greater incidence of rabies in skunks and foxes than in bats. Why do we continually hear in the news that another bat was found with rabies? Most people will bring a dead or dying bat to the public health department, but will not bring a dead or dying skunk or fox to diagnose its condition. People continue to fear bats, and when they are found in their homes the bats are often killed.

Another cause is the use of insecticides in agriculture, which are killing bats in great numbers. The insects for which the insecticides are applied are becoming resistant to the deadly chemicals. Instead being killed by the poison, the insects survive and carry the chemicals in or on their bodies. When bats consume the chemical-laden insects, the bats become poisoned and die.

What can we do to bring back bat populations?
Pressure should be placed on the agricultural industry to use natural insecticides or even to attract bats to control insects. Bat boxes can also be installed by the public in their own backyards. These boxes are specially designed structures that will attract bats and often prevents them from entering attics to roost. We can also install gates on mine and cave entrances that will prevent people from entering these areas at times when bats are very sensitive to disturbance. These are just a few ideas to aid in the return of bat populations.

Text by Scott Tremor, Field Associate, Birds and Mammals Department, and Drew Stokes
Photo credit: Mexican Long-Tongued Bat (Choeronycteris mexicana) © John Mitchell