Bats

Description

More than 40 species of bats live in the United States. Bats are the only mammals that can fly. Instead of arms or hands, they have wings. The wings have a bone structure similar to the human hand. Between the bones are flaps of skin. Bats are very light weight to make it easier for them to fly. The western pipistrelle bat weighs less than a penny, while the greater mastiff bat weighs about two ounces (57 grams).

Bats have fur on their bodies, sometimes including their head. Their wings, however, do not have fur. Bats can be a range of colors, including red, tan, brown, and gray. A bat's ears are very important because bats use them to hunt for food. The ears tend to be large and noticeable, many times sticking up on the side of the head. The Allen's big-eared bat has ears so long that they make up two thirds of its body length.

The smallest bat in the United States is the western pipistrelle bat, which grows to about 2.5 to 3.5 inches (six to nine centimeters) long with an eight-inch (20-centimeter) wingspan. The largest bat in the U.S. is the greater mastiff bat. It can grow as long as seven inches or more with a wingspan of 21 to 23 inches (53 to 58 centimeters).

Range

Bats are found throughout the United States, Puerto Rico, and the U.S. Virgin Islands. The Hawaiian hoary bat is the only native, terrestrial mammal on the Hawaiian Islands. Bats can even be found in Alaska.

Bats can be found in almost every type of habitat. They live in deserts, woodlands, suburban communities, caves, and cities. Bats make their homes (roosts) in a variety of different structures. They can use trees, caves, cracks in buildings, bridges, and even the attic of a house. The largest urban colony of bats in the U.S. lives under Austin, Texas' Congress Avenue Bridge during the summer. The Congress Avenue Bridge becomes a temporary home to more than 1.5 million Brazilian free-tailed bats.

Bats typically prefer warmer temperatures, and they have several ways of dealing with the cold. Some bats, including the big brown bat and the eastern red bat, hibernate in caves and trees to survive the winter. They can sometimes be seen flying around on warm winter days. Many bats migrate to warmer climates or even to a nearby cave.

Diet

The majority of bats in the United States are insectivores. They hunt at night and eat flying insects such as mosquitoes, beetles, and moths, many of which are considered pests. Bats provide an important ecological service by eating tons of insects. In a single midsummer night, the 20 million Mexican free-tailed bats from Bracken Cave in central Texas eat more than 200 tons of insects.

Not all bats eat insects. Some live on a diet of nectar and fruit. Bats that feed on nectar also serve as pollinators to nighttime blooming plants. To attract these flying mammals, flowering plants have evolved a musty or rotten perfume. The smell is created by sulphur-containing compounds, which are uncommon in most floral aromas, but have been found in the flowers of many plant species that specialize in bat pollination.

Vampire bats do exist, but there are none in the United States. The closest vampire bats are found in Mexico.

Behavior

Insect-eating bats hunt using a type of natural sonar called echolocation. They emit a high-frequency sound (undetectable to people) that bounces off surrounding objects. When a sound hits an object, or better yet, an insect, it bounces back to the bat's pronounced ears and gives the bat an audible map for the shape, distance, and location of nearby objects. Everything happens so quickly that a bat can make almost instant turns to catch a flying insect. A bat's echolocation system is so advanced and precise that scientists study bats to make sonar equipment for ships.

Life History

Bats are mainly nocturnal, most often flying at dawn and dusk. They fly very quickly and can make fast maneuvers. Bats congregate in large roosts during their winter hibernation and migration. In the fall and winter months, many species breed so that the offspring are born in the late spring. The births are timed with the return of insect prey.

Bats can have more than one offspring at a time. The babies are born hairless, blind, and without the ability to fly. They are completely dependent on their mother. However, it only takes a few weeks for the young bats to develop and start to fly. Despite being small, bats can have a relatively long lifespan. Bats that make it to adulthood can live into their teens; a rare few into their twenties. The hard part is making it to adulthood, because there is a high mortality rate for young bats.

Conservation

Several bat species are on the U.S. endangered species list including the gray bat, Hawaiian hoary bat, Indiana bat, lesser long-nosed bat, Mexican long-nosed bat, Ozark big-eared bat, and the Virginia big-eared bat.

Threats to bats include disease (such as white-nose syndrome), habitat loss, pollution from pesticides and insecticides, and general fear. Bats are highly misunderstood, and this can cause people to harm bats and their roosts. But bats are beneficial to people. Most bats feed on insect pests and some bats even help in pollination. Scientists study bats to further expand our understanding of flight, sound, sonar, and evolutionary biology. Even bat guano is an important resource and fertilizer.

Fun Fact

A bat's nose can be very useful characteristic for identifying a bat species. Some are small and simple, others are shaped like a pig's nose, and some even have noses shaped like leaves.

Sources

Animal Diversity Web, University of Michigan Museum of Zoology

Bat Conservation International

Defenders of Wildlife

U.S. Fish & Wildlife Service

Stoke's Beginner's Guide to Bats. Williams, K., R. Mies, D. Stokes and L. Stokes. Boston: Little, Brown and Company, 2002.