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Spotlight on Bats

Mysterious Mammals on the Fly

Source: U.S. Fish and Wildlife Service
hanging bat

ECHOLOCATION

Although bats have relatively good eyesight, most depend on their superbly developed echolocation (or sonar) system to navigate and capture insects in the dark. Bats emit pulses of very high-frequency sound (inaudible to human ears) at a rate of a few to 200 per second.

By listening to the echoes reflected back to them, they can discern objects in their path. Their echolocation ability is so acute they can avoid obstacles no wider than a piece of thread and capture tiny flying insects even in complete darkness.

In Our Encyclopedia

Bats may be the most misunderstood animals in the United States. Almost all U.S. bats, and 70 percent of the bat species worldwide, feed almost exclusively on insects and are thus extremely beneficial. One bat can eat between 600 and 1,000 mosquitoes and other insect pests in just one hour.

Bats in other parts of the world feed on a variety of items in addition to insects. Many species feed primarily on fruit, while several types feed on nectar and pollen. Fruit bats perform an extremely important function as seed dispersers. Nectar-eating bats are important pollinators. Many plant species depend almost entirely on bats for pollination.

Of the 45 species of bats found in the continental United States, six are listed as endangered. These species are the gray bat, Indiana bat, Ozark big-eared bat, Virginia big-eared bat, lesser long-nosed bat, and greater Mexican long-nosed bat.

Myths and Misconceptions

"All Bats Have Rabies."

Less than ½ of 1% of bats carry the rabies virus. In addition, rabid bats are seldom aggressive. Fewer than 40 people in the United States are known to have contracted rabies from bats during the past 40 years.

"Bats get tangled in people's hair."

Although bats may occasionally fly very close to someone's face while catching insects, they do not get stuck in people's hair. That's because the bat's ability to echolocate is so acute that it can avoid obstacles no wider than a piece of thread.

"Bats suck your blood."

By far the most famous bats are the vampire bats. These amazing creatures are found in Mexico, Central America and South America. Vampire bats feed on the blood of warm-blooded animals such as birds, horses and cattle. They do not suck blood. The bats obtain blood by making a small cut in the skin of a sleeping animal with their razor-sharp teeth and then lapping up the blood as it flows from the wound. The bat's saliva contains an anesthetic that reduces the likelihood of the animal feeling the prick. Each bat requires only about two tablespoons of blood every day, so the loss of blood to a prey animal is small and rarely causes any harm.

"Bats are blind."

Although they can't see color, bats can see better than we do at night. And, many bats can also "see" in the dark by using echolocation.

Bat Biology

Bats, like humans, are mammals, having hair and giving birth to living young and feeding them on milk from mammary glands. More than 900 species of bats occur worldwide; they are most abundant in the tropics.

Worldwide, bats vary in size from only slightly over two grams (0.07 ounce—about the weight of a dime) to more than 1.5 kilograms (more than 3 pounds). The large "flying foxes" of Africa, Asia, Australia, and many Pacific islands may have a wingspan up to two meters (6 feet). United States bats vary in size from less than three grams (0.11 ounce) to 70 grams (2.5 ounces). The largest United States bat, the greater mastiff bat occurring from central California south into Mexico, has a wingspan of approximately 55 centimeters (22 inches).

Bats are the only true flying mammals. Bats belong to the mammalian order Chiroptera, which means "hand-wing." The bones in a bat's wing are the same as those of the human arm and hand, but bat finger bones are greatly elongated and connected by a double membrane of skin to form the wing.

Bats primarily are nocturnal, although many fly early in the evening, sometime before sunset. Occasionally, especially on warm winter days, they are observed flying during daylight hours.

Reproduction and Longevity

Most female bats produce only one offspring per year, although some species give birth to three or four babies at a time. The gestation period (pregnancy) lasts only a few weeks. U.S. baby bats are born in May or June. They develop rapidly, and most can learn to fly within two to five weeks after birth. Bats live relatively long lives for animals of their small size, some as long as 30 years.

Feeding

Insect-eating bats may either capture flying insects in their mouths or scoop them into their tail or wing membranes. They then reach down and take the insect into their mouth. This results in the erratic flight most people are familiar with when they observe bats flying around in the late evening or around lights at night. Bats drink by skimming close to the surface of a body of water and gulping an occasional mouthful.

Hibernation and Migration

Because insects are not available as food during winter, temperate-zone bats survive by either migrating to warmer regions where insects are available, or by hibernating.

Several bat species hibernate in dense clusters on cave walls or ceilings. Clusters may consist of hundreds of bats per square foot. Most U.S. cave bats spend winter hibernating in caves (or mines) and move to trees or buildings during summer. A few species reside in caves year-round, although they usually use different caves in summer than winter. Most cave bats return year after year to the same caves.

Tree bats seldom enter caves. They roost in trees during summer days and spend winter primarily in hollow trees. Several species make long migration flights. The millions of Brazilian (or Mexican) free-tailed bats that spend the summer in southwestern U.S. caves migrate up to 1,300 kilometers (800 miles) to and from their winter roosts in Mexico.

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Information Please® Database, © 2007 Pearson Education, Inc. All rights reserved.

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