As night falls in the Big Thicket, look upward and you may spot a bat or two, swooping through the woods in search of insects. The only mammals capable of true flight, bats take to the skies in the evening during the warmer months.
Researchers use microphones mounted on poles to record the sounds of nearby bats.
NPS Photo / Ian Kessler
Bat Research at Big Thicket
Researchers at Big Thicket use different methods to learn about the preserve's resident bats. Recent studies have used recordings of bats' echolocation calls to determine which species are present as well as mist netting to examine the health of individual bats.
Echolocation Recording
In 2021, the NPS began conducting research about the variety of bat species that inhabit the Big Thicket. Using different kinds of equipment, researchers have been able to detect and confirm the presence of eleven bat species so far (see list below). The research is ongoing and more species will be added here when they are confirmed.
To detect the bats, researchers use a special microphone that can record bats' echolocation calls. The microphone is either mounted to a 12-foot pole or attached to a tree trunk. After recording for a few nights, the recordings are analyzed using software that identifies the calls by species. Each bat species has a unique call, similar to how birds have unique calls.
The Big Thicket's dense woods make bat detection more challenging than in other locations, such as the desert. Researchers choose locations within the preserve that will give the microphones a better chance of recording bats, such as clearings, riverbanks, and pipeline right-of-ways.
In the summer of 2023, staff from Bat Conservation International (BCI) joined Big Thicket staff on warm evenings to survey individual bats for their health.
To catch the bats, BCI researchers set up a large mist net strung from tall poles on either side of a large opening, typically across a small creek. Once night falls, staff monitor the net to see if any bats have flown into it. Once captured, researchers carefully examine the bat's vital signs and look for any signs of disease, including scarring from diseases like white-nose syndrome.
After their quick check-up, the bats are released back into the air so they can continue feasting on Big Thicket's insects.
Note: These bat surveys were conducted by trained professionals from BCI and NPS. Do not handle bats on your own!
Confirmed Species
Eleven bat species have been confirmed in Big Thicket during bat surveys:
Bat research at Big Thicket has focused on two Species of Greatest Conservation Need in Texas: Rafinesque’s big-eared bat (state threatened) and southeastern myotis. Both species live in similar habitats—bottomland hardwood forest, cypress swamp, and slope forest—and rely on hollow, large-diameter trees for roosting. Since they need big trees to survive, they prefer old-growth forest and are sensitive to human impacts on the landscape, though they have been observed roosting in manmade structures.
Researchers aim to locate roosting sites for Rafinesque’s big-eared bats and southeastern myotis so they can better protect those sites. With its mazes of bald cypress and tupelo, the Beaumont Unit has been a major focus area for bat surveys. Rafinesque’s big-eared bats have been detected there in the past but that area’s bald cypresses are threatened by saltwater intrusion and a changing climate. In order to locate the bats’ roosts, researchers aim to catch a bat, attach a temporary radio tag on its back, and release it. Then, the researcher uses an antenna to track the bat back to its roost during the day. This isn’t easy, however—catching them is a challenge because Rafinesque’s big-eared bats and southeastern myotis are rare and their populations are not concentrated like other species that roost in large colonies.
Any bat that is caught is helpful, though, as researchers can monitor the bat for its health and look for signs of disease, such as white-nose syndrome, which has affected millions of bats across North America. Additionally, researchers hope to make observations of tricolored bats, a species that was recently proposed to be listed as endangered.
This big brown bat was found roosting inside a building. (Photo from Pipestone National Monument, Minnesota)
NPS Photo / J. Borden
Bat Behavior
In contrast to the large bat colonies found in central and west Texas, bats in the Big Thicket tend to roost in smaller groups. Some bats, like the northern yellow bat, prefer to roost in Spanish moss, which is abundant in the bald cypress trees along Big Thicket's waterways. Other species roost in tree hollows, crevices behind tree bark, and in manmade structures such as bridges and buildings.
Big Thicket's bats feed on many kinds of insects, including moths, beetles, mosquitoes, ants, and even cockroaches.
Bats often forage along waterways, such as the southeastern myotis, which catches insects as it flies low over the water. According to the preliminary results of our bat study, the water's edge habitat had the most diversity of bat species. Others prefer to forage high up in the trees, like the big brown bat, which forages among the treetops.
