Austin bats favoring life under bridge still draw attention | Zoology

AUSTIN — Austin is a place that puts stock in a great many cultural symbols —breakfast tacos, Willie Nelson, Franklin Barbecue, the Capitol, Matthew McConaughey, burnt orange uniforms — yet any tour of the city’s crowded iconography would be incomplete without the bats.

The Austin American-Statesman reports you probably know the ones. They live under the Ann W. Richards Congress Avenue Bridge. About 1.5 million of them.

Mark Hollis works near the bridge, crosses it nearly every workday and is asked frequently about the bats by both tourists and out-of-town visitors to his office. He got to wondering where exactly the bats go after they begin their en masse flight from the bridge at sunset.

The short answer is they generally hunt up and down the Colorado River, but no one is sure exactly where they all go, according to Danielle O’Neil, the public engagement intern for Bat Conservation International. But before getting into the particulars, a bit of general information might help.

During part of the year, the Congress Avenue Bridge is home to the world’s largest urban bat colony.

About 750,000 Mexican free-tailed bats begin migrating in March from central Mexico to the crevices beneath the bridge. Each bat weighs about half an ounce and can fit in the palms of American-Statesman reporters who periodically have to catch one that has sneaked into the newsroom.

The Congress Avenue Bridge colony has only female adults, according to Bat Conservation International. A good time to see them is during gestation in April and May, when they’re particularly hungry. In June, most of the bats give birth to a pup (baby bat), roughly doubling the population.

The bat conservation group notes that each pup is about one-third the weight of its mother — the equivalent of a human giving birth to a 40-pound child. Most mothers stash their pups on the north — “nursery” — end of the bridge. Up to 500 pups cluster per square foot, yet the mothers manage to find their pups each night. The mothers nurse for about five weeks, until the pups are ready to fly and hunt on their own. Adult male bats cluster in other parts of town, often roosting on the sides of buildings.

Kayakers and party boats passing under the bridge each day can hear the “colony chatter,” which is more or less constant, and possibly sniff the…

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