Bats may be the most misunderstood animals in the United States, although as consumers of enormous numbers of insects, they rank among the most beneficial. Almost all United States bats, and 70 percent of the bat species worldwide, feed almost exclusively on insects and are thus extremely beneficial. In fact, bats are the only major predators of night-flying insects. One bat can eat between 600 and 1,000 mosquitoes and other insect pests in just one hour.
While most United States bat species are insectivorous, 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, including the federally-listed endangered lesser long-nosed (Leptonycteris curasoae yerbabuenae) and greater Mexican long-nosed bats (Leptonycteris nivalis), 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 federally-listed as endangered under the Endangered Species Act of 1973, as amended. These species include the gray bat (Myotis grisescens), Indiana bat (Myotis sodalis),Ozark big-eared bat (Corynorhinus (=Plecotus) townsendii ingens), Virginia big-eared bat (Corynorhinus (=Plecotus) townsendii virginianus) as well as the two long-nosed bats mentioned above. In addition to the listed continental U.S. species, the Hawaiian hoary bat (Lasiurus cinereus semotus)(Hawaii), little Mariana fruit bat (Pteropus tokudae)(Guam) and Mariana fruit bat (Pteropus mariannus mariannus)(Guam), are also listed as endangered. Twenty other species are considered to be of special concern and may be proposed for listing as endangered or threatened in the future. Populations of several of the remaining species, especially cave-dwelling species, also appear to be declining.
“All Bats Have Rabies.” Less than ½ of 1% of bats carry the rabies virus (University of Florida). 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. Far more people are killed by dog attacks, bee stings, power mowers, or lightning than rabies from bats. However, rabies is a dangerous disease so you should avoid direct contact with bats as well as other wild animals. The Center for Disease Control, USFWS, and Bat Conservation International have cooperatively developed a public health guide: Bats and Rabies.
“Bats get tangled in peoples 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 bats 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. Vampires feed on the blood of warm-blooded animals such as birds, horses and cattle. Vampire bats 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. There is an anticoagulant in the bat's saliva that helps to prevent the animal's blood from clotting until the bat has finished its meal. The bat's saliva also 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 rodents.” Bats may resemble rodents in many ways, but they are not rodents. In fact, there is recent evidence that bats may be more closely related to primates (which include humans) than to rodents (Museum of Paleontology, University of California at Berkeley).
“Bats are blind.” Although they can't see color, bats can see better than we do at night (University of California at Berkeley). And, many bats can also “see” in the dark by using echolocation.
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 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. 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.
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. Hibernation is a state of torpor (inactivity) during which normal metabolic activities are greatly reduced. Body temperature is reduced and heart-rate is slowed. A hibernating bat can thus survive on only a few grams of stored fat during the approximately five-to-six month hibernation period. Bats usually lose from ¼ to ½ their body weight during hibernation.
Several bat species hibernate in dense clusters on cave walls or ceilings. Clusters may consist of hundreds of bats per square foot. Summer "maternity" colonies of pregnant or nursing females of several species also congregate and cluster together.
Most United States cave bats spend winter hibernating in caves (or mines) and move to trees or building during summer. A few species reside in caves year-round, although they usually use different caves in summer than winter. Most cave bats are very loyal to certain caves and return year after year to the same caves, often to the exact location in the cave where they spent the previous winter.
Tree bats seldom enter caves. They roost in trees during summer days and spend winter primarily in hollow trees. Several species make relatively long migration flights between winter and summer habitats. The millions of Brazilian (or Mexican) free-tailed bats (Tadarida brasiliensis) that spend the summer in southwestern United States caves, such as Carlsbad Cavern in New Mexico, migrate up to 1,300 kilometers (800 miles) to and from their winter roosts in Mexico.