IV. Bat Behavior

Bats have been quite successful in diversifying to colonize many different environments. To thrive in their varied habitats, bats display a wide range of specialized behaviors, including echolocation, diverse diets, and hibernation.

A. Echolocation

While flying at night, bats use a combination of vision, smell, and hearing to find food, to navigate, and to avoid collisions. The Microchiroptera tend to rely heavily on a form of sonar called echolocation. In echolocation, bats emit short pulses of high-frequency sounds that are usually well above the threshold of human hearing. The sound waves spread out in front of the bat, striking any objects in its flight path and bouncing back in the form of an echo. By interpreting the echoes, bats are able to discern the direction, distance, speed, and in some instances, the size of the objects around them. Such information is instrumental in avoiding mid-air collisions and in tracking winged insects and other live prey in the dark.

Interestingly, most Megachiroptera do not use echolocation. The exceptions are the cave-dwelling Megachiroptera, who only use echolocation inside their caves. Once outside, they rely on sight.

B. Diet

More than 65 percent of bats eat insects. One of North America's most common bats, the little brown bat, can consume as many as 600 mosquitoes in an hour. Beetles account for more than a third of the diet of big brown bats, with flying ants, flies, crane flies, mayflies, stone flies, and other insects making up the rest.

Some bat species, such as the greater false vampire bat, eat small fish, reptiles, amphibians, birds, and mammals-including other bats. These bats have exceptionally long hind feet, tipped with sharp claws that are well suited for nabbing prey on the fly. Other carnivorous bats are more specialized: the fish-eating bats (also known as bulldog bats) feed mostly on fish, and the fringe-lipped bat feeds mostly on frogs. Other bats feed on fruit and nectar. Because they are fairly sloppy foragers, these bats are unintentional agents of seed dispersal and pollination, both of which help food plants to reproduce and to spread. This contributes to the health of the forest environment.

Much attention has been focused on the eating behavior of the vampire bats. These South and Central American bats feed solely on blood. They are equipped with razor-sharp incisor teeth, with which they make small incisions into the flesh of birds or mammals, lapping the blood as it seeps from the open wound. To survive, each vampire bat requires about two tablespoons of blood per day. The saliva of vampire bats contains an anticoagulant to prevent the blood from clotting. This anticoagulant is twenty times stronger than any other known anticoagulant and is used to make the medical drug Draculin, prescribed for heart attack and stroke patients.

C. Torpor and Hibernation

Bats are warm-blooded animals, but unlike most other warm-blooded animals, they maintain their body temperature only when active. During the day, while resting in their roosts, bats let their body temperature drop to the temperature of their surroundings. If the surroundings are cold, bats enter a sluggish state of suspended animation, known as torpor. During torpor, a bat's metabolism, or rate of biological activity, drops, enabling the bat to conserve energy. In the colder reaches of their ranges, many bats enter an extreme form of uninterrupted torpor, known as hibernation, that can last through the winter months. Hibernation permits bats, as well as other animals such as squirrels and mice, to conserve precious energy, allowing them to survive in the leanest of seasons when food is scarce. However, bats hibernate to a greater degree than the other animals. Whereas the body temperature of most hibernating mammals drops fewer than ten Celsius degrees (eighteen Fahrenheit degrees), the temperature of some hibernating bats can fall slightly below freezing. The coldest recorded temperature for a hibernating bat is -5° C (23° F) for a red bat.

In temperate climates, bats that do not hibernate may migrate considerable distances to winter roosts in warmer locales where food is more plentiful. For example, the Mexican free-tail bat migrates nearly 1600 km (nearly 1000 mi) between summer roosts in the United States and winter roosts in Mexico. Magnetic materials in the brains of some species may help measure the earth's magnetic fields, providing subtle clues that enable migrating bats to find their way over great distances.