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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. Bats are second only to rodents in numbers among mammals and comprise about one-fifth of all mammal species. 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 (Eumops perotis) occurring from central California south into Mexico, has a wingspan of approximately 55 centimeters (22 inches). Bats are the only true flying mammals, and their maneuverability while capturing insects on the wing is astonishing. Bats belong to the mammalian order Chiroptera, which means "hand-wing." The bones present 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 are primarily 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. Most United States bats breed in autumn, and the females store sperm until the following spring when fertilization takes place. The gestation period (pregnancy) lasts only a few weeks, and 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. 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. 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. Information for this Web site was taken almost exclusively from: Bats of the United States Published by In Cooperation with the Copies of this publication are available from the Service's Asheville, North Carolina Field Office (828) 258-3939
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