Fantastic Bats!

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Holy Diversity!

Bats are members of the order Chiroptera, a Latin word meaning “hand wing,” a reference to the creatures’ handlike wing bones. Although we think of bats as uncommon and seldom-seen, their numbers reveal the truth. Of the roughly 5,400 mammal species on our planet, about 1,100 are bats — in other words, about one out of every five mammal species is a bat. Their diversity is so extraordinary that biologists further divide the order by size, into Megachiroptera, or megabats, and Microchiroptera, or microbats. Megabats are found only in the tropics and are collectively known as flying foxes, for their foxlike faces. The biggest of these are the giant flying foxes, the world’s largest bats, which weigh as much as 3.5 pounds and have wingspans of up to 6 feet.

Microbats, at the other end of the spectrum, occur worldwide and include the planet’s smallest mammal, the bumblebee bat of ?Thailand. The contrast with its flying-fox cousins is astounding: A bumblebee bat has a wingspan of about 5 inches and weighs four one-hundredths of an ounce, or about as much as one paper clip.

All of the 46 bat species that live in the United States and Canada are microbats, ranging in size from the balloon-eared western mastiff bat, with a wingspan of 22 inches, to the diminutive western pipistrelle, which weighs barely more than a penny and is about 2.5 inches long. Actually, most of our bats are decidedly small, but their spread wings make them seem bigger. One of our most common “large” species — the big brown bat — has a wingspan of up to 13 inches, but weighs only half an ounce.

Of course it’s not just size that defines diversity among bats-ghost-faced bat, mustache bat, horseshoe bat, hammer-headed bat, bulldog bat, leaf-chinned bat and slit-faced bat.

Although many tropical bats feed entirely on fruit or flower nectar, and a few swoop down over water to snag fish or frogs for dinner, more than 70 percent of all bat species feed on insects. This includes all bats in the United States and Canada, except for three nectar-sipping types that live along the U.S./Mexican border.

Most bats hunt by night and sleep by day. The majority are social animals and roost in groups or colonies, the largest of which — a colony of Mexican free-tailed bats living in Bracken Cave in central Texas—numbers more than 20 million. For roosting sites, most bat species prefer attics, caves or abandoned mines. Other types of bats are solitary tree dwellers that hang out in trunk hollows or from leaf-sheltered branches.

Winter Break

In late summer or early fall, because colder weather means fewer insects and the coming of winter, most North American bats either migrate or hibernate. Some species travel south as far as Mexico, but most move shorter distances to a hibernaculum, usually a cave or abandoned mine, where the temperature constantly remains a few degrees above freezing. Here, the bats go into a torpor; their breathing and heart rates slow, and their body temperatures fall from about 104 degrees to around 40 degrees. Even in this slow-burn state, a bat has just enough stored fat in its small body to get through the winter. If the temperature inside the cave increases, or if the bat is awakened, its metabolism speeds up and it will likely use up its stored fat and starve. In some cases, even brief disturbances by humans have wiped out whole colonies of hibernating bats.

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