ANR-757, Reprinted October 1996. H. Lee Stribling, Extension Wildlife Scientist, Associate Professor, Zoology and Wildlife Science, Auburn University

Bats And Bat Houses

Bats are among the most misunderstood animals in Alabama. Because they are secretive and active only at night, bats are often feared and needlessly killed. Contrary to common myths, bats are neither blind nor dirty. They do not get caught in people's hair or infest homes with bedbugs.

Like other mammals, a few (less than 0.5 percent) contract rabies. But even rabid bats rarely become aggressive or transmit the disease to other animals. When people are harmed by bats, it is usually because they have foolishly picked up a sick bat that bites in self-defense. Records show that pet dogs are far more dangerous.

Bats Are Valuable

One bat may eat 3,000 or more insects, including many mosquitoes, in a single night. Large bat colonies can consume billions. The Blowing Wind Cave colony of gray bats in northern Alabama, numbering roughly 300,000 individuals, eats up to a billion insects nightly!

Fruit-eating bats are nature's most important seed-dispersing mammals. And nectar-eating bats, along with some fruit bats that visit flowers, pollinate thousands of tropical and subtropical trees and shrubs. The extensive list of valuable fruits, nuts, and spices produced by bat-dependent plants includes peaches, bananas, mangoes, guavas, avocados, dates, figs, cashews, carob, and cloves.

Bats use highly sophisticated sonar for navigation, and they are exceptionally long-lived and disease resistant. Consequently, they are becoming increasingly important for research. In the southwestern United States, 100,000 tons of bat guano (bat droppings) was mined from a single cave. Guano continues to be a major source of fertilizer in developing countries, where it is used to fertilize a number of crops.

Bat Biology

Bats, like human beings, are mammals. They have hair and give birth to young that feed on milk produced by the mother bats. Forty species of bats occur in the United States, and sixteen of those occur in Alabama.

Bats are the only mammals that truly fly, and they make their living by capturing insects. Most of their feeding is done at night although they may fly in the early evening and during daylight hours on warm winter days.

Although they have good eyesight, they use echolocation (sonar) to navigate and capture insects. Bats emit high-frequency sound pulses (human beings cannot hear them) at a rate of 3 to 500 per second. By listening to the echoes, they can "see with their ears."

Most birds that catch insects "on the wing" use their mouths or beaks. Bats usually capture insects by scooping them into their tail or wing membranes. They then reach down and take the insects into their mouths. This feeding behavior results in the erratic flight pattern you see when watching a bat feed at dusk. Bats drink by skimming close to the surface of a water source and gulping occasional mouthfuls.

Most female bats produce one offspring per year. Alabama bats breed in autumn, and the female stores the sperm until spring, when fertilization takes place. Gestation is short, lasting only a few weeks, and baby bats are born in May or June. The young can fly 2 to 5 weeks after birth. Bats are long-lived for their small size: they can live 30 years or longer.

Few insects are available during the winter, so bats must migrate to warmer areas where there are more insects. Bats that do not migrate must hibernate to survive. Hibernation is a state of inactivity during which the nominal body functions are greatly reduced. For example, a bat's temperature drops from the normal 100 degrees F to between 40 degrees and 60 degrees F during hibernation. The heart rate slows from 1,000 beats per minute to 12 to 15 per minute. During hibernation, bats live off of stored fat reserves.

Many bats in Alabama hibernate in caves during the winter and move to buildings or trees in the summer. Tree bats roost in trees in summer and move into hollow trees or caves in the winter.

When Bats Meet People

Human Habitat. Occasionally a bat may wander into human living quarters. To prevent this occurrence, cover chimneys and vents with hardware cloth screens, install draft guards beneath appropriate doors, and seal other access holes, especially around windows and plumbing.

Large colonies of bats in attics or walls can become a nuisance and might require eviction. In these instances, observe the bats carefully at dusk to find their entry-holes. Plug these holes while the bats are out feeding or during their winter absence. Poisons used against "house bats" are costly and ineffective, and they often create problems far worse than those they are supposed to solve.

Bat Habitat. Millions of bats have been killed by people who explore caves. Although some people intentionally kill bats, many others are unaware of the damage they do. Each human entry into a winter hibernating cave causes bats to arouse and waste 10 to 30 days of stored fat reserve. Hibernating bats must conserve their limited fat supplies until spring or face starvation. In the summer, flightless young may be dropped or abandoned when human beings disturb nursery roosts.

The relatively few caves that shelter bats are seldom used year-round. Warm summer nursery caves should not be explored from April through September. Colder hibernation caves should be avoided from late August through mid-May. Many important caves have signs explaining when they can be visited without harm to the bats.

Alabama's Endangered Bats

Two bats that occur in Alabama are classified as endangered species. They are the gray bat and the Indiana bat. The Endangered Species Protection Act mandates stiff fines and possible imprisonment for those who kill or disturb endangered bats or harm their habitat.

What Can You Do To Help Bats?

Never shoot, poison, or otherwise harm bats. Bats are extremely beneficial insect-eaters. Nuisance bats can be encouraged to move elsewhere without killing them.

Avoid maternity colonies and hibernating bats. Disturbances, no matter how slight, can be harmful.

Do not disturb bat habitats. Cave habitats are fragile and easy to disturb. If you enter caves, do so only as an observer. Leave everything as you found it. Remember, disturbing endangered bats is a federal offense and carries serious penalties.

Put up a bat house. They are easy to build and can attract bats to help control insects around your home and garden.

Construction And Placement Of Bat Houses

Bat houses, like those shown in Figures 1 and 2, have been used successfully for a variety of bat species. Regardless of the kind of house you build, the inner surfaces must be rough enough for the bats to climb. Do not paint your bat house: paint or varnish may be a repellent to bats. Rough-sawn cedar or cypress is best to use because no painting is needed.

Bat houses should be fastened to a tree trunk or the side of a building about 12 to 15 feet above the ground. The best place is where they will get morning sun but will be shaded in the afternoon.

Sometimes bats move into a bat house within a few weeks. However, bats may require a year or two to find a new bat house. Chances of early occupancy can be increased by hanging your houses before April. Houses are usually occupied more quickly if bats are already present in nearby barns or attics.

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References

Information in this publication was adapted from:

Arkansas Bats: A Valuable Resource, by Michael J. Harvey, Arkansas Game and Fish.

Suggestions for Building Bat Houses and Attracting Bats, by Bat Conservation International, Milwaukee, Wisconsin.

About Your Bat House, by Bat Conservation International, Austin, Texas.

Bats and Their Conservation, U.S. Fish and Wildlife Service, Washington, DC.