Texas Parks and Wildlife biologists, volunteers work to monitor fatal bat disease

Jeff Davis County Wildlife Biologist Olivia Gray with Texas Parks and Wildlife uses a flashlight to locate hibernating bats underneath a bridge. Bats are being tested for a fatal disease, white nose syndrome, across the state this winter. Photo by Mary Cantrell.

FAR WEST TEXAS — Local Texas Parks and Wildlife (TPWD) biologists are working with the help of volunteers to test overwintering bats nesting under bridges and in caves and mines for a fatal fungal disease known as white nose syndrome. 

The disease progresses from the presence of a fungus called pseudogymnoascus destructans, which can grow on bats when they are in torpor, an inactive state in which their body temperatures are lowered. Bats are irritated by the disease and come out of torpor to scratch themselves, burning precious calories, and die of starvation as a result. 

TPWD biologists are currently swabbing bats for the disease around the state. In the tri-county area and in Terrell and Hudspeth counties, those efforts are led by Krysta Demere, TPWD wildlife diversity biologist covering the Trans-Pecos region. Demere was a part of the team that first detected the spores of the fungus in 2017 in the Texas panhandle. 

White nose syndrome originated in Europe and was discovered in the United States for the first time in the winter of 2006-2007. An online map shows how the disease has since progressed from occurring primarily on the East Coast to spreading across the country. 

“Since that point in time, bats all across the country, but mainly starting in New York, were falling out of their roosts during the winter. They’d find them on the landscape; the ground would just be littered with [dead] bats,” said Demere. 

By 2020, the presence of the spores led to the development of the disease in Texas, said Demere, primarily affecting bats in Central Texas where the majority of the state’s cave systems are located. 

“In 2020 we started documenting bats come out of hibernation and just fall across the landscape,” said Demere. “People were calling into parks and wildlife: ‘I found a dead bat on a hiking trail. What should I do?’ ‘I found a dead bat in a parking lot.’ It was really in 2020 that we documented the actual diseases here — white nose syndrome itself.” 

Millions of bats have died in the U.S. due to white nose syndrome, according to the White Nose Syndrome Response Team, a group organized by the U.S. Fish and Wildlife Service. Demere explains that the mortality rate of colonies affected by white nose syndrome can be as high as 90 to 100 percent, and there is concern that certain species, including cave myotis, which hibernate in large numbers in Central Texas over the winter, will be wiped out. 

“We’re extremely worried about that specific species, and we’re doing everything we can to not only monitor that species but any other wintering bats we have in Texas,” said Demere. 

Demere began swabbing hibernating bats in West Texas for the first time in the winter of 2020-2021. Samples are sent off to Northern Arizona University for testing. Her first year, all of the samples she sent in came back negative for the fungus except for one Mexican free-tailed bat she swabbed in Big Bend Ranch State Park in Presidio County. 

“That was the first documentation of the fungus anywhere out here in West Texas,” said Demere. “Mexican free tails, even if they carry the spores, haven’t actually developed the disease, so they could be more of a carrier. But it’s the other bats that they could come into contact with that we’re worried about.” 

This winter, Demere is out swabbing bats again, beginning with all of the bridges she visited two years ago, but expanding her reach to local caves and abandoned mines in Shafter, Big Bend National Park, Guadalupe National Park and more. Demere, with the help of Texas Master Naturalist volunteers and fellow Jeff Davis County Wildlife Biologist Olivia Gray, has been working to survey areas for dead bats, count roosting bats, fluoresce bats with an ultraviolet light to see if they can pick up any indication of the fungus, and swab the bats for samples. 

“Any help that I can get from volunteers is great. This is all work that I can do by myself, but it goes by a lot faster and smoother having extra hands,” said Demere. 

TPWD biologist Krysta Demere carefully collects samples taken from area bats which will be sent to the lab. Testing will reveal whether the fungus which causes white nose syndrome is present in local bat populations. Photo by Mary Cantrell.

Bats are often found roosting in cracks under bridges. Using what she calls the “bat tickler” — a dowel rod with a swab-sized hole drilled into the end of it — biologists and volunteers are able to get into the cracks too narrow for human hands in order to reach the bats. Bats often make noises in protest or open their mouths to bite the swab (researchers are often targeting their noses for the samples). Gray joked that she felt like she was brushing bat teeth. 

So far this year, Demere said she has encountered significantly fewer bats than she did in the winter of 2020-2021. She said she has definitely seen less of the cave myotis species particularly. The first bridge she visited in Brewster County, the site of a known myotis maternity colony that has housed a sizable population of bats in the past, was almost entirely empty this year. 

“I only found one bat in the entire bridge this year. That’s a little scary for me,” said Demere. 

Other bridges recently surveyed showed declines from 1,500 to 133 bats and 500 to 121 bats over the course of two years. The severe winter storm that took place two years ago, after Demere visited the bridges, and the more recent December cold snap could be to blame for the struggling populations, said Demere. Most bat species have one to three young a year, meaning their populations are slow to recover. 

Texas is known to be home to over 30 bat species. The majority of the bats Demere and volunteers have come across are Mexican free-tailed bats, with the exception of a singular bat of the Yuma myotis species, known to exist near water. Is it possible that the bats that remain in Texas for the winter are juveniles who are unaware they are supposed to fly south for the winter. 

But even today, said Demere, little is known about the migratory patterns of bats — transmitter technology, which allows scientists to track animals’ movements, has previously been limited. 

“The bats are tiny, most of them are less than 10 grams. So having a transmitter that you can put on something that small — [the technology is] just now getting there,” said Demere. 

In addition to bats being a huge tourist attraction in the state of Texas — sites including the Congress Bridge in Austin, the largest urban bat colony in the world, as well as Bracken Cave in San Antonio, the largest congregation of any mammal on the planet, attract thousands of visitors — bats eat their body weight in insects every night and contribute to a balanced ecosystem. 

Bats are estimated to provide $3.7 billion worth of assistance to farmers for their pest management services, according to the White Nose Syndrome Response Team. 

“People do not realize how important bats are to the agriculture industry. Farmers already spend a ton on pesticides, and that is with the help of bats; the amount of money that would have to be spent to battle those pests without that would be astronomical because bats take care of a huge portion of insects that target our crops,” said Demere. 

Mexican free-tailed bats located underneath a bridge in Jeff Davis County. Photo by Mary Cantrell.

The region is also home to a breeding population of the Mexican long-nosed bat, an endangered nectar-feeding bat which travels north from Mexico in the spring to spend summers in Emory Cave in the Chisos Mountains of Big Bend National Park. The Mexican long-nosed bat is the main pollinator of agave plants, which are used to produce tequila. 

Other studies, including an agave and yucca study at the Chinati Mountains state natural area, have also taken place. 

“We would not have tequila without that bat,” said Demere. “Because the disease has not been found this far west and south before we have no idea what it’s going to do to a nectar feeding bat like the Mexican long-nose.” 

They plan to continue monitoring efforts and may make management decisions based on this year’s results, said Demere.  

Fort Leaton State Historic Site in Presidio is another popular roosting site in the area for bats; its crosshatch wood ceilings are home to hundreds of Mexican free-tailed bats in the summer. The site also put in a giant bat house near the structure that is also utilized by bats, though nowhere near the level of the fort, said Thomas Forwood, the site’s superintendent. 

“Guano clean up is a daily morning routine for us once it warms up a bit,” said Forwood, referring to the accumulation of bat excrement.

While there is a lack of day-to-day personal accounts from the early days of Fort Leaton in general, and none mentioning the presence of bats, Forwood said the flying mammals have likely been there since the site’s inception; the layout of the site has remained the same throughout history. 

“It’s been a perfect roost site. We figure since the early days of Fort Leaton bats have definitely utilized this structure,” said Forwood.

The fort’s Mexican free-tailed population leaves the site to fly south during the winter months, meaning they do not have a large hibernating colony or “hibernacula” — this makes the population fairly low risk, so the fort does not actively swab for white nose syndrome. The fort also sees Yuma myotis and cave myotis species. Canyon bats, a species of concern for the disease, are also found at nearby Big Bend Ranch State Park. 

Park employees keep an eye out for sick or dead bats and alert natural resource specialists as needed, said Forwood. While the populations of bats at Fort Leaton aren’t of immediate concern for white nose syndrome, Forwood said there is still a lot to be learned about the disease and its spread in the West. 

“There’s a lot of question marks, so that’s some of the reason that there’s a lot of research and a lot of concern,” said Forwood. “It’s a concern for ones that have similar physiology to ones in the East that have been affected hard, but also for what’s going to happen here.”