Bats

Forrest M. Mims III

Shortly after sunset in tropical and temperate latitudes, dark objects can be seen rapidly zipping and zapping across the twilight sky. These objects are bats.

Bats are among the most amazing of all mammals. They range in size from the tiny bumble bee bat of Thailand to the giant fruit-eating fox bats of the Philippines.

The bumblebee bat is smaller than the end of a man’s thumb. The fox bat has a wing span that reaches nearly 2 meters!

Where I live in South Texas, the most common flying mammals are Mexican free-tailed bats (Tadarida brasilensis).

It's winter in the northern hemisphere as this is written, and those bats are vacationing in Mexico. In several months, they will return to plucking mosquitoes, moths and other insects from the night sky. They do this with amazing efficiency, for a single bat may capture hundreds of insects each hour!

Texas is home to millions of Mexican free-tailed bats each spring and summer. Most of these bats form huge colonies that roost in limestone caves. Carlsbad Caverns in southern New Mexico has the best know bat colony in the US. But some Texas caves also host huge bat colonies.

These large colonies are apparently all females, at least until June when the pups are born. Normally bats hang upside down when they perch. While giving birth, the female hangs with her head up and catches the newborn in the membrane between her back legs. She may even carry the newborn with her on her nocturnal flights for a few nights.

Baby bats, like baby birds, grow up fast. They are able to fly after a month or so.

One of the largest bat colonies in central Texas doesn't’t spend its days in a cave. Instead, it roosts in the crevices and crannies under the Congress Avenue Bridge over the Colorado River in Austin.

The Congress Avenue colony is estimated to number 1.5 million bats. Each evening those bats consume vast quantities of insects, with estimates ranging from five to ten tons per night!

Years ago when the bats started roosting under the Austin bridge, some citizens were fearful they would bring diseases like rabies. Instead, they brought tourists.

No longer afraid of the bats, people now watch them stream out from under the bridge each spring and summer evening. The bats can be seen from various restaurant patios, boat tours and from the Austin American-Statesman newspaper's Bat Observation Center on the south bank of Town Lake east of the bridge.

You can find out much more about bats at the library or on the web.

Forrest M. Mims III and his science are featured online at www.forrestmims.org.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.