Flying mammals that can be found in nearly every habitat, except extremely hot deserts and extremely cold polar regions.
The fact that bats can fly makes them unique among mammals. Flying squirrels and flying lemurs, despite their names, do not really fly. Because they do not have wings, they merely glide through the air as they jump from trees. Bats, however, have wings that are the result of millions of years of evolutionary development.
Bats belong to the order Chiroptera, a word that means hand-wing. There are two suborders: Megachiroptera, which includes 42 genera and 173 species of flying foxes and Old World fruit bats, and Microchiroptera, made up of 144 genera and 813 species. The members of the first suborder are found only in Europe and Asia. Flying foxes have foxlike faces with very large eyes, but, unlike other bats, they do not use echolocation, a kind of natural radar for finding insects and other objects.
Echolocation is a process used by bats and a few other animals to identify objects in their environment and measure their distance from them. This ability involves listening to echoes of sounds produced sent by the hunter to bounce off his prey. A person who shouts in a tunnel and listens for the echo is using a simple form of this process. Because animals of the suborder Microchiroptera have this natural radar, they are much more successful and widely distributed than animals of the suborder Megachiroptera. Bats are among the most numerous mammals in the world’s rainforests. In some forests, bats pollinate or disperse the seeds of more than 30 percent of all trees.
The oldest bat fossils date to about 60 million years ago, and show that bats are native to North America. Scientists believe that the ancestors of bats were tiny, mouse-like mammals that ate flying insects and lived high up in trees. Over time, these animals developed membranes between their forelegs and their bodies that gave them the ability to glide from branch to branch, much like modern flying squirrels. This membrane gradually transformed into a moveable wing that gave bats a major advantage over their rivals: the ability to fly above the trees to catch their prey.
Students of bat evolution speculate that early species had developed the ability to echolocate, which gave them the ability to catch flying insects at night, but the exact origin of this power is unknown. Bats are sometimes compared with birds, because both can fly. However there are about eight times more species of birds than bats. This is because bats are a younger group than birds, which means they developed their flying ability long after birds took to the air. Another difference between birds and bats is that bats cannot use their legs, which are attached to their wings, to swim, dive, run, or dig. Birds’ legs are separate from their wings and can thus be used for food gathering and other activities.
True flight offers many advantages to creatures, such as bats, birds, and insects, that have the ability. Flight gives these creatures access to many new sources of food and is a very effective way to evade enemies and predators. Flight also makes long-distance migrations possible and allows animals the ability to get past obstacles, such as rivers, oceans, and mountains, which flightless species cannot cross without difficulty or assistance. Flying also requires less energy than other modes of movement, such as walking or swimming. Bats and birds use less than one-fourth of the energy used by land-based animals for locomotion.
Most animals have not developed the complex structures necessary for flight. The basic requirements for flight include a method of keeping the body above the ground (lift), a means of moving the body through the air (thrust), and a design that minimizes air resistance. The bat’s wing provides both lift and thrust. It contains the same basic arm and hand bones found in all mammals, except that the bat’s five finger bones are very long and slender.
The membranes used for flight are extremely thin sections of skin, which are stretched between the arms, fingers, body, legs, and feet. Although they appear delicate, the membranes are actually stronger than rubber gloves and can be torn only with great force. The muscles that move the wing are located on the chest, back, and shoulder. This arrangement allows bats to fly with less energy than if the muscles were on the wing. Because bats’ legs are used more for flight than for moving around on land, their pelvises and legs are very small, giving their bodies a streamlined, slender body shape that cuts down on air resistance.
Bats achieve lift and propulsion by the downstroke of their wings. The lift is caused by air moving faster over the top of the wing than under it. To increase their speed, both bats and birds increase the speed of air moving past their wings by changing the angle of the downstroke and changing the curvature of the wing. Most bats begin flight by taking off from a roosting site. Bats spend more than one-half of their lives roosting in places, such as caves and trees, in which they are protected from both weather and predators. They hang upside-down resting in their roosts, usually during the day.
When hunting, bats eat a wide variety of foods, including pollen, fruits, leaves, mosquitoes and other insects, scorpions, fish, frogs, birds, and sometimes even other bats. Most bats are intelligent and can be trained to fly or walk through mazes. They can also be taught to respond to commands. The activities of bats are regulated by light. Because they are active mainly at night, they avoid competition with birds for food. They can also escape from being captured by owls, hawks, and falcons.
Altringham, John, Tom McOwat, and Lucy Hammond. Bats: Biology and Behavior. Reprint. London: Oxford University Press, 1998. An indispensable reference covering the natural history of bats with up-to-date information and fine-line illustrations. Hill, J. E., and J. D. Smith. Bats: A Natural History. Austin: University of Texas Press, 1984. A description of all bat species in the world and their habitats. Tuttle, Merlin D. America’s Neighborhood Bats. Rev. ed. Austin: University of Texas Press, 1997. A popular natural history of bats, including facts on their behavior and biology, with identifying photos, keys, and range maps for common species.
Evolution of animal flight
Forces of flight