On the outskirts of Calhoun on a warm morning early last month, three Georgia Department of Natural Resources (DNR) wildlife biologists carrying flashlights led a group of 20 people beneath a noisy overpass.

As 18-wheelers and SUVs rumbled overhead, the DNR staff pointed their lights up into the concrete beams above, revealing rows of furry, winged mammals hanging upside-down fromthe bridge’s narrow joints, apparently unfazed by the commotion above.

There are 16 bat species found in Georgia, where the situation facing many of those — plus dozens of others across the U.S. — is bleak.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

The nonprofit Bat Conservation International (BCI) released its first-ever “State of the Bat” report last month, finding that more than half of this country’s 154 bat species are at risk of steep population declines in the next 15 years. Many species have already been decimated, with several factors to blame, including habitat loss, climate change and a deadly fungal disease.

But even as they face numerousthreats, scientists say bats are resilient, opportunistic creatures. And as human development shrinks their natural habitat, experts say the animals, whichhelp control pests that plague people and farms, are making their homes in the man-made structures that replace them.

This overpass on I-75 in NorthGeorgia is one example. An estimated 72,000 vehicles zoom across the bridge every day, but in recent years, scientists have discovered its underbelly is also home to 2,000 to 3,000 bats, making it one of the largest-known bridge-roosts in the state.

Trina Morris, a veteran program manager with the Georgia DNR who has studied bats for a quarter-century, estimates 10% to 20% of the bridges in the state have some bat use. In South Georgia, as many as half of the drainage culverts built to channel water under roads and highways, are home to bats, she said.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

Morris and other DNR officials are training Department of Transportation staffers and contractors working in Georgia and beyond to spot signs of bat use — especially by endangered ones — to try to help stem losses that have affected many species.

At the same time, they are working closely with the DOT and other state agencies to develop new practices that allow critical road and bridge repairs to move forward without harming the bats that use them, too.

“We know that these structures — though they aren’t natural — provide a refuge for our bats,” Morris said. “So being able to determine which areas are most important for them is really something that we can do to protect them.”

Multiple threats

Many bat experts say that the winged creatures have a bad rap, dogged by stubborn misconceptions that they are bloodthirsty, disease-ridden animals.

Bats can carry rabies, but they also provide many benefits for humans, scientists say.

While not all species feed on insects, the ones that do — including many native to Georgia — are voracious eaters that help keep pests in check. In an hour, a single bat can devour hundreds of mosquitoes.

“Georgia is a great place for insects to thrive and without bats out there eating them in very large numbers every night, insect populations would be much higher — at levels I think we couldn’t even fathom,” said Dr. Amanda Adams, the director of research coordination at the bat research nonprofit BCI.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

Bats also help farmers by feeding on some of the most destructive pests found in Georgia, from the wood-eating emerald ash borer to the corn earworm moth, Adams said. Without them, farms would need to spray even more pesticides to keep the bugs at bay, she added.

The populations of many bat species are in free-fall, in large part due to human activity.

New building and development is leading to tree loss and disturbing caves, shrinking habitats for many species. Climatechange-fueled heatwaves and droughts, meanwhile, are also causing mass bat casualties, the BCI report found. On the blustery Great Plains, the spinning blades of wind turbines pose another threat.

Then there is white-nose syndrome. The fungal disease causes weight loss, dehydration and eventually death in most bats that contract it. While it has been present in Europe and Asia for years, it emerged in the Northeast in 2006 and has since spread to Georgia and 38 other states, plus much of Canada.

The disease has sent populations of all bats in North Georgia’s caves plummeting by 90%, according to the Georgia DNR. The tricolored bat, one of the smallest species found in North America, has been hit especially hard. The bats are still found in Georgia but last year, the U.S. Fish and Wildlife Service proposed listing them as endangered, citing a growing risk of extinction, mainly because of white-nose syndrome.

“Our bats only give birth one time a year, they have one or two pups, mortality is high and they live a long time,” said Katrina Morris, the program manager with Georgia DNR. “It’s really not easy for that kind of an mammal to recover quickly.”

‘A simple thing we can do’

With bat populations falling and their natural habitats shrinking, avoiding unnecessary disruption of roosts in man-made structures has become even more critical. But spotting signs of bat habitation can be difficult.

Back in May, deep inside a North Georgia culvert, Georgia DNR biologist Emily Ferrall showed a group of trainees what to look for. Toward the end of the massive drainage tunnel, which runs under the entire width of I-75, two on-ramps and an adjacent railroad, Ferrall pointed with her flashlight up at a tiny hole in the concrete overhead. Inside, a single, rare tricolored bat was resting.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

Species like tricolored bats can squeeze into openings only a quarter of an inch wide. When they can’t be seen, the potent ammonia-like smell of their urine can be a tip-off.

Morris said DNR began regularly surveying transportation structures for bats roughly 10 years ago. Since then, the agency has become a regional leader in teaching those who build, repair and design transportation infrastructure about the animals, plus working with partners to adapt projects to minimize bat disturbance.

Today, anywhere from 50 to 100 environmental consultants and DOT staff from across the Southeast take the agency’s “Bats in Bridges” field training course each year. During the May session observed by The Atlanta Journal-Constitution, there were participants from Georgia, South Carolina and the U.S. Department of Agriculture.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

One of those was Marvin Bouknight, a wildlife biologist from Catawba Nation, the only federally recognized Native American tribe in South Carolina. He said the tribe recently began surveying some of its culverts for bats and found signs of use by several species.

Bouknight said he was already thinking of ways their existing infrastructure could be retrofitted and made more appealing to roosting bats.

“Instead of plugging (culverts’ drainage weep holes), maybe we can just cap them and that’ll leave more area for the bats to roost,” he said. “That’s just a simple thing we can do. But why not, right?”

Building with bats in mind

In Georgia, efforts to look for and consider bats in infrastructure projects are already yielding results.

In 2018, when the bridge near Calhoun where the group of trainees stopped needed its expansion joints replaced and its road surface re-coated, Georgia DNR and DOT developed a plan forthe critical maintenance that protected the bats, Morris said.

The work was conducted overnight, when most of the bats would be away from their roosts. And before applying the protective coating, DOT workers inserted flexible foam into the bridge joints to shield the bats from being sprayed or hit by debris. The work was monitored by both DNR staff and U.S. Fish and Wildlife Service officials, and the agencies said no bats were harmed.

Credit: HYOSUB SHIN / AJC

Credit: HYOSUB SHIN / AJC

“This was a really good opportunity for us to figure out a way to make slight modifications so that work that has to be done could happen,” Morris said. “And the project didn’t cost more.”

In the years since, DNR has worked on other transportation projects, she said. Depending on the project, acoustic deterrents and artificial bat houses can sometimes be used to temporarily clear bats from infrastructure. Morris said her staff also pushes for roosting habitat to be included in any new construction.

“These structures are really important for these species, whether we intended it that way or not when they were built,” Morris said.

A note of disclosure

This coverage is supported by a partnership with 1Earth Fund, the Kendeda Fund and Journalism Funding Partners. You can learn more and support our climate reporting by donating at