When they’re not in caves or trees, or possibly making nuisances of themselves in attics, it turns out many bats like to hang out under bridges. So many, in fact, that the Georgia Department of Transportation factors them in when it’s planning construction or maintenance on a bridge.
Bat City
Biologist Carrie Straight crouched under a highway bridge north of Atlanta. She had scrambled up the concrete slope from the country road below. Traffic sped just a few feet over her head on Interstate 75.
“Overall the bridge has got to have thousands of bats,” she said. “Easily within viewing distance there’s a couple hundred right where we’re sitting up under this bridge.”
Straight is a biologist with the U.S. Fish and Wildlife Service. She first checked this bridge for bats earlier in the summer, and when she found how many were here, she said she was in awe.
The bats were wedged into cracks between slabs of concrete, nestled together and on top of each other forming rows and rows of bats, all tucked into the bridge.
This isn’t a big, famous bridge. It’s outside of Calhoun. The kind of bridge that people driving 70 miles an hour down the highway would barely notice.
“It’s amazing,” said Pete Pattavina, another Fish and Wildlife Service biologist.
He and Straight are both based in Athens.
“A roost this big probably would be extremely uncommon before we started building these large, massive monolithic structures,” he said.
Most bridges don’t have as many bats as this one, said Pattavina. Many don’t have any bats. But there’s also a bridge in Austin, Texas, that’s become famous for the 1.5 million bats that roost there in the summer.
Basically, without meaning to, humans have built bat cities all over the place.
Safe Haven
At another bridge, Pattavina and Straight found about 45 sleeping bats. Straight said it was a maternal colony: mostly mother bats cuddled up with their pups. Bridges are great habitats for the animals, said Straight, because heat from the road seeps down and keeps the bats warm, and the bridges provide cover for the baby bats.
“It looks pretty cozy,” said Straight, looking up at the little colony.
The bats at the bridge were a species called big brown bats. They’re not endangered, but Pattavina said state law requires agencies to consider impacts on them, just like they would for any wildlife. That’s where the Georgia Department of Transportation comes in.
“It becomes very expensive if an environmental concern is found during construction,” said Pattavina. The DOT doesn’t want to get a contract going with cranes and workers, he said, then find it has to stop and wait.
So the biologists, with help from the Georgia Department of Natural Resources, check out bridges ahead of time, to see if the DOT can plan its maintenance schedule around baby bats that can’t fly yet; or find a way to work on a bridge without disturbing a bat colony. Pattavina said if there was a safety issue on a bridge, and it needed to be fixed right away, concerns about bats wouldn’t hold up that process.
Pattavina pulled one of the bats off the bridge to get a closer look. It was a male, the size of a mouse with a tiny bulldog face. He looked right at the biologists, squeakily expressing how cranky he was at being held. Pattavina laughed at how expressive the bat was.
“They’re very intelligent. They’re very curious. They know what’s around them in their environment,” he said. “They are addictive. Once one starts to work with bats, it’s hard to go back.”
Bats In Crisis
But this is a rough time to be a fan of bats.
Pattavina let the little bat go, then reached back into a far corner under the bridge to pick up a dead bat. He cupped a tiny pile of fur and pine-needle-sized bones in his palm.
“This is the remains of a tri-colored bat, that probably died this winter from white nose,” he said.
White nose is a syndrome that’s killed millions of bats in North America. It’s caused by a fungus that infects hibernating bats. It wakes them up in the dead of winter; they go out in search of food, and then starve to death.
Pattavina said even if there was a cure, it’d be pretty much impossible to treat all the bats in all the caves that would need it.
Some species, including the big browns, haven’t been affected, said Pattavina, but smaller species, like the sad fluff he was holding that had been tri-colored bat, are being devastated.
“It’s hard to put into words, what it’s like to see animals dying. I mean people love animals,” he said. “And even though bats are chronically misunderstood, they are really important to the functioning of our ecosystem.”
That’s another reason why the work on bridges is important, said Straight.
“[We’re] trying to preserve what we can preserve,” she said. “When you find a roost, trying to do something about it.”
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