Web Extra: Bats and Bridges

The 1980s discovery that the crevices beneath Austin’s newly reconstructed Congress Avenue Bridge had inadvertently created prime bat-roosting habitat (eventually housing the largest urban bat colony in the world) led to a new appreciation of how modern structures can impact these beneficial creatures. And this, in turn, has resulted in changes in bridge-design policy in Texas and throughout the United States and the world.

One of the heroes in this chain of events was Mark Bloschock, a TxDOT bridge engineer who has since retired. In 1994, Bloschock and other TxDOT engineers began a joint study with Bat Conservation International, Inc. (BCI) to investigate, among other things, where and under what circumstances bats prefer to roost and raise their young and why the bats had settled under the Congress Avenue Bridge in the first place. The study found that slot-shaped crevices under the bridge were similar in size to spaces found in bat caves. It also showed that bridges and culverts were among the favored man-made roosts for many bat species and uncovered bat-roosting preferences related to these structures. It also indicated that minor modifications to highway structures can maximize or minimize the potential for use by bats.

After completing the study, TxDOT embarked on “a program to design and retrofit bridges and culverts (when it is appropriate and economical) with bat roosts in mind.” Since then, the Bats and Bridges program has spread to 24 states and 17 countries. Because of his efforts, Bloschock received an award of excellence from BCI, the first the organization has given to anyone outside the wildlife conservation field.

Bloschock, who remains active in conservation, notes that bat habitat in bridges is encouraged or discouraged depending on several factors. “Central to the decision to include possible bat habitation are the type of bridge superstructure and the locations of these bridges,” he says. “When the bridge-beam type that is known to attract bats is being specified anyway, the decision to include bats requires no additional cost. By using the knowledge of bat preferences obtained through the Bats and Bridges Study performed with BCI, the right details can be specified in the original bridge design that encourage bat habitation. The bridge locations that are prime bat-roosting habitat are in rural areas and over bodies of water.”

For additional information, see an online brochure about the Bats and Bridges Program, which includes a partial list of bat-viewing locations.

From the June 2012 issue.

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