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6:21 p.m. Fri, Dec. 19th

Hordes of hungry bats both delight and darken Austin

Jul 28, 2011, 6:23 a.m.

By Karen Brooks

AUSTIN, Texas (Reuters) - There are 1.5 million bats living under a bridge in downtown Austin, and a historic Texas drought is making them hungrier than ever.

That's bad news for the bats in the world's largest urban bat colony. But it is good news for the humans who gather each evening just a few blocks from the state Capitol building to watch their spectacular nightly trips into the nearby Hill Country to find food.

The drought has killed off crops in Texas, and that in turn has killed off those delicious pests the Mexican free-tailed bats consider dinner.

That means they have to leave home earlier than usual each night to find nourishment -- giving the locals in this bat-crazy city a precious few more minutes to watch the normally-nocturnal critters fly before the sun goes down.

Each night they stream from under a bridge by the hundreds of thousands in a black cloud so large that it shows up on local weather radar.

"It's wonderful for people to be able to see them, and they are really spectacular," said James Eggers, director of education for the Austin-based Bat Conservation International. "But it's an indicator that things are a little tougher for the bats."

It is tougher on some of the humans as well.

"They're attracting the tourists to the bridge earlier in the evening, that becomes a serious impediment to getting across the river for Happy Hour," said Austin resident Lawrence Collins, who was only half joking.

The daylight departure is a bittersweet phenomenon, enjoyable to bat lovers only because naturalists do not see any negative long-term effects if the drought ends soon.

"If we just have one to two years of drought, it's a natural cycle and it's not going to affect the species as a whole," Eggers said. "What some scientists fear is that this is not a regular drought, but could be indicative of change coming because of global warming. If we have an extended drought for many years, that could affect the population of the Mexican free-tails."

An extended drought could be a double whammy for central Texas farmers, who depend on the bats to remove some 1,000 tons of insects and pests from the air each night.

A study in 2006 showed that area cotton farming, which was a $4.5 million-a-year industry at the time, saved some $750,000 a year from pestilence thanks to the Mexican free tails.

Some 100 million bats live in Central Texas, experts say. The largest bat colony in the world resides in a cave northwest of San Antonio, with more than 20 million bats living there. The Mexican free-tails summer in central Texas and winter in Mexico.

Around March, about 750,000 pregnant females come to downtown Austin and nest under the Congress Street bridge, just blocks from historic Sixth Street and the governor's mansion.

A few months later, they have their babies -- one offspring per year -- and their numbers double to 1.5 million. The nightly spectacle, which draws visitors from all over the world, lasts through about October, when the bats return to Mexico.