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Bats | |
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Introduction A bat's small, furry body looks somewhat like that of a mouse, and at one time was thought to be a flying mouse. "Flittermouse " is the name once given to this animal. At other times the bat was likened to being a bird. Many fables relate these likenesses--as bird, mouse, and bat.
Flight Bats are expert fliers. They have gone beyond the gliding and parachuting abilities of flying squirrels, lemurs, and possums. They are capable of true flight. Of the nearly 4,000 mammal species on earth, bats are the only mammals capable of powered flight. Although a bat's body is adapted to flight (the neck is short, the chest is massive with powerfully developed muscles, and the abdomen is narrow and tapering), in order to fly a body must have a wide, thin surface (airfoil) and the power to push it through the air (propulsion). In a bat, it is the wings that are both the airfoil and the propulsion system. Among vertebrates, bats, as well as birds, have been able to conquer the skies in active flight because of their wings. A bat's wing consists of bones that are very similar to the bones in a human arm and hand. Thus the name given to this animal order: "chiroptera", which is Greek for handwing. Long arm bones, with extra-long extended finger bones, are covered with a double layer of thin skin called a membrane. The membrane (or patagium), which looks similar to the skin between the toes of a duck's foot, is so thin you can see light through it. It is made up of fine blood vessels, elastic fibers and muscle fibers. The fibers help keep the flight membrane taut and aid in folding of the wing membrane when the bat is at rest. The membrane stretches over the arm bones and extended finger bones to the sides of the body and leg forming an airfoil surface. In some bats, this flight membrane may also extend between the legs and include the tail. The small clawed thumbs (often used for climbing) are left free. The second and third fingers, along with the membrane in between, give the wing a stiff leading edge similar to an airplane's, while the third finger forms the wing tip. Little flight advantage is found in bat species where the membrane is extended to include the tail. In bats that do have the tail membrane, it serves more to slow them down than to steer. In some bat species it is used as a pouch when catching insects. Bats fly through the air in a rowing motion. On the downstroke, the wing moves backwards and upwards. Then the wings are swung outwards and downwards. Finally they are drawn forward with the tips drawn almost together in front of the head forming the shape of an open umbrella. On the upstroke the wings are moved first upwards and then backwards. Many bats may fold their wings on the upstroke to reduce air resistance, but it is during the downstroke that both thrust and lift are achieved. Similar to birds, strong, large muscles provide powerful wing strokes that enable flight. While birds use the strong muscles fastened to their large breastbone, bats move their wings by using the large muscles in their backs and chests. Some of these muscles pull the wing up, while others bring them down. A bat's wings act like webbed hands. The bat can move its wings like we move our fingers enabling it to change its wings' shape rapidly to dart, flip, and turn quickly. Although birds use their tails to brake and steer, bats use their wings by folding one wing for a second and using one independently of the other. Many bats have also mastered hovering flight, similar to hummingbirds and helicopters, that enables them to remain stationery in flight, while other bats are able to achieve brief periods of gliding flight. Microbats/Megabats The animal order, chiroptera, is divided into two main groups of bats: micro-chiroptera (microbats) and megachiroptera (megabats). Microbats is the larger bat group consisting of over 700 species that are found in the Americas and throughout Asia, Europe, Africa, and Australia. Bats in this group are smaller in size with complex ears and small eyes that probably only see in black and white. They rely more on echolocation (listening to echoes to find objects) to hunt for their diet of insects, fish, or frogs.
Echolocation works like the radar or sonar in planes or ships. A bat sends out beeps through the air that hit an object and bounce back as echoes. The bat hears the echoes and its brain works out a sound picture of the object. It can tell if the object is prey or part of the landscape. The unusually large ears and large nose leaves of some microbats aid in echolocation.
The wing area of microbats is smaller than their body size. These insect eating bats must make up for their small wing size by increasing their number of wing strokes. They raise and lower their wings from 11-18 times per second. These small, fast moving wings enable microbats to change direction quickly and sometimes even hover in flight while hunting. Most microbats do not travel great distances but, instead, hunt in the immediate area for insects.
Megabats is the smaller group of bats consisting of approximately 170 different species that live in the tropical areas of Africa, Asia, and Australia. The bats in this group are larger bats with simple ears and large, dog-like eyes. They are often called flying foxes because of their foxlike faces or fruit bats because of their diet. Contrary to what many people think about bats (they are all blind and use echolocation), these bats use their keen vision and sense of smell to navigate and locate nectar, pollen, and fruit to eat. Most have no echolocation ability. The wing area of these fruit eating megabats is larger than their body size. Wings often reach spans of 2 meters with wing beats of as few as 7 per second. Due to the air resistance on its large wings, megabats appear to be slow and ponderous in flight. But with long narrow wings, it is not unusual for megabats to travel 50-80km in one night to feed.
Bats Today Bats make their homes in barns, attics, caves, and hollow trees--any place that is cool and dark. Although they usually live in small groups, sometimes hundreds of thousands live together in a colony. The Bracken Cave in Texas is the largest known colony with a population of 20 million Mexican free-tailed bats. Most bats are nocturnal and thus do most of their flying at night. Using their wings and often their tails to scoop up insects as they fly, many bats eat up to half their weight in insects on a night. One little brown bat can eat up to 600 insects in an hour, while a colony can rid us of 6,000 tons of insects in a year. While feeding on their diet of fruit, tropical bats not only transfer pollen as they fly from plant to plant, but also contribute to growing the plant. They can digest their meal of bananas, mangoes, guavas, and berries in 15-20 minutes. They then pass (defecate) the undigested seeds of these fruit while flying, often reseeding clear-cut areas of the rain forest.
In some areas of the American Southwest, desert plants such as saguaro and organ pipe cactus are dependent on bats for nighttime pollination. In turn, animals such as ground squirrels and elf owls are dependent on these plants for survival. The loss of bats in these areas would mean the loss of large numbers of plant and animal life.
Some unique kinds of bats include: California Leaf-Nosed Bats live in the western United States and Mexico and catch their diet of bugs by listening for their footsteps or wing beats.
Hog-Nosed Bats of Thailand are the tiniest bats and the world's smallest mammal. They are about the size of a bumblebee and weigh less than an ounce. They have the wingspan of about 5 inches.
Gray Bats are endangered and live in only nine caves in the United States.
Vampire Bats live in Mexico and Central and South America. They do not suck people's blood, but do feed on the blood of sleeping cattle or livestock.
Flying Foxes aren't really foxes, but are the largest bats known with a wingspan of up to 6 feet.
Misconceptions
Unfortunately, many people think of bats as dirty, rabid creatures linked with evil forces of darkness, witches, and Count Dracula. On the contrary, bats are very clean animals who, similar to birds, groom their wings (and in the case of bats, even their teeth) regularly. They are no more carriers of rabies as any other mammal, and there is no truth to the belief that they change shape during the day and turn into bats only at night. In reality, bats are very beneficial to man and the environment.
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In the sixth century B.C. Aesop was said to have related the
story of a weasel and a bat. A weasel had caught a bat while
hunting for birds. The quick-witted bat claimed he was not a
bird, but a bat and was released. A short time later the same
bat was captured by a weasel who was hunting for mice. This
time the bat claimed he was not a mouse, but a bird and again
gained his freedom. (Schober, The Lives of Bats, p. 9)
