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Curious Fact of the Week: The Nightly Flight 1.5 Million Bats from an Austin Bridge

Congress Bridge Bats in Austin, Texas

This month marks the return of one of the most startling spectacles of the natural world: the 1.5 million bat colony that migrates to an urban bridge in Austin, Texas.

From mid-March through November, Mexican free-tailed bats congregate under Congress Bridge in downtown Austin. And as each day falls into dusk they emerge in clouds of tiny screeching creatures. This is the largest urban bat colony in the continent, although there are larger groups of the bats that inhabit caves around Texas and into Oklahoma, Arizona, and New Mexico.

Congress Bridge Bats in Austin, Texasphotograph by Kenneth Hagemeyer

Congress Bridge Bats in Austin, Texas
photograph by Peter17/Wikimedia

The bats were an ominous occurrence following a bridge renovation in 1980 that added expansion joints. Unbeknownst to the bridge engineers, they were designing a perfect bat colony. However, while the initial reaction of the city was one of fear for rabies and the other reactionary beliefs that the little animals tend to provoke, Austin has now embraced the bats and there are now cruises that take boats beneath the bridge to witness the nightly departure for foraging. The local minor-league hockey team has even been named after them — the Austin Ice Bats — with a logo showing a bat gripping a hockey stick in its claws. Besides, at 1.5 million, the bats outnumber humans in Austin 2:1.

Congress Bridge Bats in Austin, Texasphotograph by Lars Plougmann

As Bat Conservation International explains, these bats migrate from Mexico and are mostly female, using the bridge as a maternity colony (so you are likely to see baby bats out on their first fly amongst the crowd). The BCI also emphasizes that although the sight can be unsettling, the bats are “gentle and incredibly sophisticated animals” that eat some “10,000 to 20,000 pounds of insects, including agricultural pests” on the nightly flights. Each bat only weighs about half an ounce, but its consumption can seriously cut into the mosquitoes that also swarm in summer.

The Congress Bridge bats are most numerous on the hottest, driest nights, and if you’re nocturnal yourself you can witness them return to their bridge home just before daybreak.

To find out what time the bats are departing Congress Bridge for the night, you can call a Bat Hotline (512-327-9721 Ext. 16) or check the Bat Conservation International site for estimated emergence times.

CONGRESS BRIDGE BATS, Austin, Texas


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