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November 2009 cover image bicycle riding at Big Bend Ranch State Park

Home, Sweet Bat Home

Simple retrofit turns ordinary bridges into homes for bat colonies.

By Angela Lindfors

Tourists and locals alike gather with their eyes on the sky every clear summer evening at the Congress Avenue Bridge in Austin. The object of their fascination is not the sunset; they have gathered to witness the flight of more than 1.5 million Mexican free-tailed bats from their home under the bridge and into the mosquito and moth-rich Austin airspace.

Since the colony formed there, a series of studies have been launched and completed by the nonprofit Bat Conservation International (BCI) and the Texas Department of Transportation(TxDOT). Initial concerns included worries about the stability of a bat-laden bridge and public safety, but the studies show that the bat presence is actually beneficial to people, not only in Texas, but in the entire United States.

Some bats can consume up to 1,000 mosquitoes in a single hour. Every year, bats eat billions of mosquitoes and other pests that might otherwise be dealt with by farmers and suburbanites with chemicals. Bats are nature’s own flying insect control mechanism. Farmers in the United States likely save millions of dollars in pesticides and crop damage, thanks to large bat colonies — many of them in Texas — stopping the insects at their source before they migrate to the crops of the upper Midwest. In addition, tourists who come to see the Congress Avenue Bridge bats bring nearly $8 million into the local economy.

Bats, for all their usefulness, are quickly declining in number as their natural habitats are compromised. The Texas Department of Transportation and BCI hoped to replicate such a successful bridge colony elsewhere, to provide homes to bats in places where they are needed.

One such example is Canadian Middle School in the Texas Panhandle. More than 30,000 Mexican free-tailed bats made the school attic home, causing local concern. Students and teachers, with help from BCI, TxDOT and local businesses, retrofitted a nearby bridge, providing a new home for the bats to roost when they were ousted from the attic.

A 1994 survey by bridge engineer Mark Bloschock found that only 0.01 percent of Texas highway structures were suitable for bat roosts, but many of them could work with minor changes. Currently, 218 Texas highway structures are inhabited by bats, and Bloschock’s Bats and Bridges program is now being used in 25 states. The changes are usually simple and inexpensive, and can be accomplished using recycled highway signs. Retrofitters are able to influence what type of bat they attract by how they build the structures under the bridges, and can regulate the size of the colony by the number of crevices added. They can also be upsized, downsized and even moved, if necessary. So far, every retrofit effort has ended successfully.

Farmers and engineers aren’t the only ones trying to attract bats. BCI encourages people all over the United States to build bat houses. While not all species of bats eat mosquitoes, all North American bats are considered beneficial. Urban bat colonies will eat many garden pests, as well as mosquitoes hatched in man-made pools of stagnant water, such as retention ponds and unused fountains. With proper education about bat safety, there is no reason not to invite some warm-blooded flying neighbors to your neighborhood.

Want to attract some bats to your yard? Go to www.batcon.org/index.php /get-involved/install-a-bat-house.html to build your own bat house. Or, by shopping around, you can buy a pre-made BCI-certified bat house for as little as $60.

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