- Associated Press - Monday, March 14, 2016

AUSTIN, Texas (AP) - Austinites are endeared to the more than 1 million bats that make their summer home beneath the Congress Avenue Bridge. But that structure is not the bats’ only urban habitat, and a different bridge project has been slowed to save the nighttime creatures that live inside.

Last week, construction workers began replacing the deteriorating mortar in the historic West Sixth Street Bridge, but not without first devising a plan, with the help of Bat Conservation International, to save the small colony of Mexican free-tailed bats roosting in the bridge’s crevices.

Workers inspected the crevices, which vary from a half-inch to 3 inches across. Some openings were shallow; others were so deep that endoscopes and cameras were needed to see inside, public works engineer Pirouz Moin said. The workers often found two or three bats living in each crevice, usually marked by stains from oils secreted by the bats.

Next, the crews placed rounded pipes, pointing downward, beneath each crevice to allow the bats to exit safely. The bats are not able to re-enter through the pipes, which are smooth inside and prevent them from gripping the sides with their claws.

However, bats are able to move to other open crevices in the bridge, so workers have to keep a close eye on the project and continue to fill in mortar one section at a time.

The pipes must stay in place for at least a week of more than 50-degree days before they can be removed and filled with mortar. If bats enter other crevices, pipes will be moved to these sections.

Meanwhile, construction crews are filling in mortar in areas of the bridge where bats are not living.

Bat exclusion is a meticulous process - one that added 15 days to the project and $9,000 to the already $90,000 in construction costs.

“It’s not an easy thing to do,” Dianne Odegard, a public outreach specialist with Bat Conservation International, told the Austin American-Statesman (https://atxne.ws/1QFBAHb). “It does take some patience and some care to make sure you are not entombing bats. And that’s the whole idea of doing an exclusion. You just want to make sure that you are not sealing bats into a bridge. That’s absolutely not the right answer.”

The nonprofit Shoal Creek Conservancy hired a consulting company to inspect the bridge, built in 1887, as part of a larger restoration process. They came across chips in the mortar holding the stones together, which prompted the city to undergo an immediate repair out of safety concern.

It is not unusual for Mexican free-tailed bats to stick around during the winter months. However, the rush of more than a million female bats to the Congress Avenue Bridge, which draws about 100,000 tourists annually, usually begins at the end of March and lasts through October.

The population under the West Sixth Street Bridge is expected to be cleared out in about two weeks. Odegard said bats do not leave their roosts every night, especially when the weather is unpredictable or unseasonably cold. After they leave, they will find other suitable places to live, most likely beneath the other bridges along Shoal Creek, where they have access to water insects.

The Shoal Creek Conservancy is continuing to raise funds to clean graffiti off the bridge, place a protective coating over it and add lighting and signs that will highlight the historic significance of the bridge, which predates the Capitol and helped open up areas of West Austin to development.

The Mexican free-tailed bat, a red-brown or often gray bat, weighs a half-ounce and has a wingspan between 12 and 14 inches, making it an extremely fast flier. Its usual life span is about 18 years. And while its population is not threatened or endangered, its females give birth to only one pup every summer, in early June. They roost in caves and attics, under bridges or in abandoned buildings, usually near water, which attracts the insects they eat. They typically migrate to Central America and Mexico during the winter and return to our region in late March.


Information from: Austin American-Statesman, https://www.statesman.com

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