Bat is the only mammal that can fly. Like other mammals, bats are warm-blooded, have fur, and nurse their young with milk. Unlike other mammals, bats have wings. Bats fly around searching for insects, fruit, or other food. People do not often see bats because bats usually come out only at night. By day, bats roost in various places, including buildings, caves, crevices, foliage, and tree hollows. Many bats roost by hanging upside down, but some roost sideways or standing upright. Bats are generally small compared to other mammals.
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Bats vary in size and appearance. The largest bats, called flying foxes, have wingspans of up to 6 1/2 feet (2 meters) and can weigh more than 3 pounds (1.4 kilograms). They have roughly pigeon-sized bodies. Kitti’s hog-nosed bats, sometimes called bumblebee bats, are the smallest bats and probably the smallest mammals. They weigh about 0.07 ounce (2 grams). Bats that roost in dark places often have dark fur. Bats that roost in more exposed locations, such as among foliage, may have colorful red or yellow fur.
Some people think that bats are blind. But although most bats are color blind, all bats can see and many species have excellent vision. Bats also have highly developed senses of smell and hearing. Like dolphins and whales, many bats can sense their surroundings using echolocation. In echolocation, the animal uses echoes of sounds it produces to collect information about its surroundings.
More than 1,000 species (kinds) of bats exist. They live everywhere in the world except the northern Arctic, the Antarctic, and some remote islands. Most bats live in tropical and subtropical regions, but some live as far north as Alaska, Scandinavia, and Siberia.
Many people think that bats are frightening or even dangerous. But bats generally try to avoid people and may even benefit them. For example, some bats feed on insect pests, helping to control their numbers.
The body of a bat
Bats have the same basic body parts as all mammals. A bat’s body, however, is highly adapted for flight. The adaptations include not only the wings but also internal processes that regulate the animal’s use of energy.
Wings and legs.
A bat’s wings are highly modified arms and hands. Long arm and finger bones support the wings, giving them their shape. A thin membrane of skin connects these bones to one another and to the bat’s body, forming the wing’s surface. The membrane is usually black or grayish-brown, but it can be reddish-orange, white, multi-colored, or translucent. A bat’s thumb, which sticks out from the top of its wing, can be tiny or long and often features a claw.
A bat’s wings can vary from short and broad to long and narrow. The size and shape of the wings affect the way a bat flies. Bats with long, narrow wings, for example, can generally fly fast. Bats with short, broad wings typically fly more slowly but can lift heavier loads. Some bats can fly at speeds of more than 30 miles (48 kilometers) per hour.
Bats fold up their wings when they land. Most bats have weak legs, so they walk somewhat awkwardly using their thumbs and wrists as well as their feet. A special structure in the tendons (connective tissues) locks the feet of many bats in a clamped position, enabling the bat to hang upside down while resting. Some species use adhesive disks on their thumbs and feet to cling to smooth surfaces.
Internal regulation.
While flying, bats use a great deal of energy, which heats up their bodies. To protect from overheating, flying bats use their wings to shed heat from their bodies into the air. Roosting bats, on the other hand, try to conserve energy and avoid losing body heat to their surroundings. In cooler weather, many kinds of bats conserve energy by lowering their body temperature to match the air temperature—an unusual ability among mammals. Other bats lack the ability to control their temperature. They have a constant body temperature, much like other mammals.
A bat’s heart rate can vary greatly, depending on its activity. For example, the heart of the little brown bat beats more than 1,000 times per minute while the bat flies. When the bat lands, its heart rate drops to about 200 to 300 beats per minute. While the little brown bat hibernates, its heart rate can drop to under 10 beats per minute, and the bat barely uses any energy. 
Digestion.
Most bats have small, sharp teeth that they use to reduce food to a soupy texture. Food moves rapidly through a bat’s digestive tract, taking as little as 20 minutes to pass through the body. Quick digestion helps bats to avoid carrying extra weight while flying.
Face.
Many kinds of bats are named for their unusual faces. Leaf-nosed bats, for example, have a leaf-shaped flap of skin on the nose. Horseshoe bats have U-shaped nose flaps. The faces of wrinkle-faced bats have a deeply wrinkled texture. Some of these facial features probably help focus sound for use in echolocation.
The life of a bat
Most bats are nocturnal (active at night), roosting during the day. Some bats roost alone, but other bats roost in colonies. A single cave may house millions of bats. Bats do not build nests. Some bats, however, make tentlike structures out of leaves for protection from sunlight, rain, and predators.
Some bats can live more than 30 years. But most bats probably do not survive their first year in the wild. Many young bats die during or shortly after birth. In temperate climates, the survivors often struggle to accumulate enough fat to sustain them through their first hibernation. Bats have few natural predators, but certain animals will catch and eat bats. These animals include other bats, birds of prey, cats, raccoons, and snakes.
Food.
Bats living in temperate climates, such as those living in the United States, Canada, and Europe, are insectivorous (insect-eating). Some insectivorous bats eat their own weight in insects each night. Tropical bats feed on insects as well as fruit, leaves, nectar, and flower pollen. Vampire bats feed on blood. Some bats eat birds, frogs, lizards, mice, and other bats.
Water.
Many species of bats lap up water with their tongues as they fly near the surfaces of ponds or streams. Bats also obtain moisture from the food they eat, and certain bats do not need to drink much water. Some bats living in deserts probably never drink water.
Echolocation
helps bats locate prey and avoid obstacles during the night, when bats are most active. However, bats probably use vision and memory more than echolocation to navigate from place to place.
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Bats can modify the frequency or pitch and duration of echolocation calls to suit their needs. Most bats cannot call and listen for echoes at the same time. However, certain bats, such as horseshoe bats, can call and listen at the same time. They distinguish the call from the echo based on the frequency of the sound.
Echolocating bats make distinctive echolocation sounds, which biologists can often use to identify the bats’ species. Certain beetles, lacewings, mantids, moths, and other insects can hear bat echolocation calls, which helps them avoid being eaten by bats.
Hibernation and migration.
Some bats migrate to other areas when food becomes scarce. Many bats in Europe and North America, for example, migrate southward to warmer climates during the winter because the cold weather causes insect prey to become scarce.
Other bats move to sheltered places, such as caves or mines, to hibernate during the winter. A hibernation site typically provides stable temperatures that remain above freezing. Many bats require high levels of humidity in their hibernation sites to reduce the amount of body moisture lost through evaporation. Bats depend entirely on their stores of body fat to survive hibernation. Waking requires more energy than remaining in hibernation. Bats disturbed and awakened during hibernation, therefore, might not retain enough fat to survive the winter. For this reason, people should avoid disturbing hibernating bats.
Some tropical bats, such as mouse-tailed bats, estivate during hot seasons. Estivation, like hibernation, is a state of dormancy (inactivity), but it protects the animal from heat and dryness instead of cold. Estivating bats also rely on large body fat deposits to survive.
Reproduction.
In many species of bats, the males and females live in different roosts—sometimes even in different geographical regions—but come together to mate. The length of pregnancy varies from around 40 days to nearly a year in some species. Generally, larger species have longer pregnancies. In many species, pregnant females gather in special nursery colonies during pregnancy and nursing.
Some bats, such as plain-nosed bats, time their reproduction in an unusual way. The bats mate in late summer or early fall. But instead of immediately becoming pregnant, the female stores the sperm in her uterus (womb) through the winter. After waking from hibernation, she becomes pregnant. Other bats, such as the Jamaican fruit-eating bat, may become pregnant before the winter, but then delay development of the embryo during hibernation. In such species, a female bat can remain pregnant for many months.
Most bats have one baby at a time and give birth only once a year. But some species have litters of two or more, and many tropical species breed multiple times per year. A newborn bat generally weighs about a fourth as much as its mother. The young bat typically consumes its own weight in milk each day, which can be demanding for the nursing mother to produce. Bats nurse from around three weeks to up to nine months, with smaller species generally nursing for shorter periods.
Some kinds of bats
Some kinds of bats, such as brown bats, are extremely common. Other kinds, such as vampire bats, are widely known for their interesting habits.
Brown bats
include the big brown bat and the little brown bat, sometimes called the little brown myotis. Both species are widespread in the United States and Canada. Big brown bats weigh about 0.4 to 0.9 ounce (11 to 25 grams) and typically have wingspans of about 12 1/2 to 14 inches (32 to 35 centimeters). Little brown bats are about half the size of big brown bats. Both types of bats eat flying insects and occasionally roost in buildings. They hibernate through the winter.
Brazilian free-tailed bats,
also called Mexican free-tailed bats, are one of the most numerous species in the Western Hemisphere. They live in North, South, and Central America, and throughout much of the Caribbean region. These insectivorous bats weigh from about 0.4 to 0.5 ounce (10 to 15 grams). The bats roost in caves and buildings. Some of them live in colonies of tens of millions of individuals. The bats range widely in search of insects, sometimes flying as high as 10,000 feet (3,000 meters) to feed on migrating moths. Many of the bats themselves make seasonal migrations. Some populations of Brazilian free-tailed bats living in North America move south during the winter, while some living in southern South America move north. Loading the player...
Bat attacking a moth
Carnivorous bats
eat the meat of animals, such as fish, frogs, lizards, and mice, as well as other bats. These relatively large bats weigh from about 0.7 to 5 ounces (20 to 150 grams). Some fish-eating bats have large, clawed hind feet that they use to capture their prey.
Fruit bats and flower-visiting bats
are common in tropical areas. Fruit bats mostly eat ripe fruit. Flying foxes are fruit bats. They live in Africa, India, Southeast Asia, and Australia. In the tropical regions of the Western Hemisphere, certain species of leaf-nosed bats eat fruit. Flower-visiting bats are related to fruit bats and also live in tropical areas. They mainly feed on the nectar and pollen of flowers.
Red bats and hoary bats
are insectivorous bats widespread in the Western Hemisphere. The individual bats live by themselves. They roost in foliage and migrate during the winter. Hoary bats are the largest bat species in Canada and the United States, weighing from about 0.7 to 1.2 ounces (20 to 35 grams). Red bats are generally about half the size of hoary bats. Female hoary bats usually bear two young in a year, but can bear up to four at a time. Female red bats usually give birth to litters of two to four young bats.
Vampire bats
eat the blood of such livestock as chickens, cows, horses, pigs, and sheep. Some of them also eat blood from birds and other animals, sometimes even human beings. They bite out small scoops of skin about 1/5 inch (0.5 centimeter) wide and deep. Their saliva promotes bleeding from the wound. The bat usually feeds once per day, eating about 1 to 2 tablespoons (15 to 30 milliliters) of blood from each victim. The three species of vampire bat all live in South and Central America. They weigh about 1 ounce (30 grams) and have wingspans of 13 inches (33 centimeters) or more.
Unlike most bats, vampire bats have relatively strong leg bones. They can run on the ground, using their legs, elongated forelimbs, and powerful wings. Vampire bats also nurse their young for an unusually long time, up to nine months.
Bats and people
Myths about bats range from fantastic stories about vampires to simple misconceptions. For example, many people believe that bats try to become tangled in people’s hair. But healthy bats generally try to avoid people. Some people think bats are dirty animals. But bats typically spend much time cleaning their bodies and wings.
Bats can help people in many ways. Some species may help control insect pests and maintain the natural environment. Fruit bats scatter plant seeds in their droppings. Like bees, flower-visiting bats pollinate flowers.
Like other mammals, bats bite in self-defense and may carry the deadly infectious disease rabies (see Rabies ). Rabies spreads through bite wounds, so people should avoid handling bats.
Human activities can harm bats. People harm bats by destroying the places where they live or by disturbing bats during hibernation. Some bat species are in danger of dying out completely.
In the 2000’s, millions of hibernating bats were killed in North America by a disease called white-nose syndrome . The disease is caused by a fungus.
