by Samra Jones Bufkins, Elm Fork Master Naturalists
Texas is home to more than 30 species of bats, with at least seven known to live in Denton County. Texas’s large size, with most of the land privately owned, presents challenges to the study of these critical flying mammals. Their value for insect control and pollination is enormous for the Texas agricultural community.
LLELA is one of 18 sites in Denton, Cooke, and Wise Counties participating in an acoustic bat monitoring project led in partnership with the Elm Fork Chapter of Texas Master Naturalists and Texas Nature Trackers (TNT) of Texas Parks & Wildlife Department.
Habitat loss and fragmentation, along with the presence of White-Nose Syndrome and other issues affecting bats, emphasize the need for more knowledge about the distribution of these creatures. Traditionally, bats were studied using mist-netting and roost counts. However, the passive collection of data using acoustic monitors has enabled researchers to expand their knowledge about bats worldwide.
Cooperation Between Elm Fork & Texas Parks and Wildlife
In early 2023, Craig Hensley of the TNT staff began discussing the idea of incorporating acoustic monitoring of bats in partnership with Texas Master Naturalists, who are among the many conservation and education volunteers working at LLELA.
Acoustic monitoring involves recording the echolocation calls of bats in the overnight hours as they feed. Echolocation is a physiological process for locating distant or invisible objects (such as prey) using sound waves reflected back to the emitter (such as a bat, whale, or dolphin) by the objects. Bats use echolocation for orientation, obstacle avoidance, food procurement, and social interactions.
Contrary to popular belief, bats have excellent eyesight. However, because they feed at night, they rely on echolocation to locate food sources, such as flying insects, more efficiently. Echolocation pulses consist of short bursts of sound at frequencies ranging from as low as about 1,000 hertz to as high as 212,000 hertz. The pulses are repeated at varying rates (often in a single individual, depending upon the situation), beginning at about one per second. The rate may reach several hundred per second (e.g., in a bat close to its target).
Because their echolocation sounds are inaudible to humans, specialized equipment and software are needed to record and analyze their calls to determine which species of bats are likely to be active within the study area.
Monitoring locations were selected based on data collected by partners of North American Bat Monitoring Program, using ARCInfo software and an algorithm that prioritized Generalized Random Tessellation Stratified (GRTS) cells based on the probability of the presence of bats. ARC GIS mapping helped select 18 sites in the three counties covered by the Elm Fork Chapter.
Bat Monitors at LLELA & in North Texas
Two sites were selected for monitors at LLELA in areas not usually accessible to the public: Barn Owl Ridge and the area between the greenhouses and the turtle compound. Installed about six feet off the ground on a Monday in Spring/Summer 2024 and removed the following Friday, data was downloaded and scrubbed of noise using specialized software.
The data analysis team — made up of Elm Fork TMN members Sue Hudiburgh, Clarissa Molina, and Brynne Bryan — spent many hours staring at “blue blobs” on their computers and learning to distinguish the unique sonograms of the various bat calls recorded. The volunteers attended multiple training webinars and several in-person and Zoom meetings with TNT staff; Wildlife Acoustics, the makers of monitors and software; and other data analysts throughout Texas. The first year of the project presented a steep learning curve for all involved, requiring patience and attention to detail. Proudly, everyone persevered.
Craig cautioned that the software did not necessarily guarantee a bat species was present. “We really don’t know if a bat has been anywhere unless we’ve held it in our hand at that location,” he frequently stated. Various parameters, including accuracy ratios and number of pulses, were employed to determine a “high probability” of a given bat’s presence.
LLELA Bats Include Vulnerable Species
Five bat species determined to have a high probability of residing at LLELA during the study period were Eastern Red Bat (Lasiurus borealis), Evening Bat (Nycticelus humeralis), Hoary Bat (Lasiurus cinereus), Seminole Bat (Lasiurus seminolus), and Tri-colored Bat (Perimyotis subflavus).
The Tricolored Bat is listed as endangered in several states and is under consideration by the U.S. Fish & Wildlife Service for inclusion on the Endangered Species List under the Endangered Species Act. The Hoary, Evening, and Seminole Bats are listed as Vulnerable in Texas.
Education About Bats Underway
As word about the project spread throughout the community, master naturalists have conducted several presentations on bats and staffed bat information booths at area events. Volunteers gave a well-received presentation to a homeschool group that then created a bat craft using items found in nature.
“In addition to promoting conservation awareness, we hope that through our outreach efforts, bats will become beloved by those who previously viewed them as merely creepy creatures of the night,” said Mary Morrow, co-project manager.
The 2025 study period is underway, with monitors placed at last year’s locations, plus new locations along the shoreline of Lake Bridgeport in Wise County and another in Cooke County near Whitesboro. All involved look forward to sharing the information they have learned with the community, including Friends of LLELA.
Eastern Red Bat Lasiurus borealis
The most abundant migratory tree bat in North America
Size: 3.75” to 4.5” long, weighing 7 to 13 g (0.2 to 0.5 oz)
Wingspan: 13”
Appearance: Bright copper reddish orange fur. Males are brighter red, females and juveniles are grayish. Both have white patches of fur on the front of their shoulders.
Habitat: Generally live alone or in family groups of mother and young, in grasslands with patches of trees, forests, and riparian areas. Daytime roosts can be the outer canopy of large trees, agricultural edges, shrubs, and bushes. They hibernate in hollow trees or under loose bark as well as leaf litter on the ground. They often hang from tree branches and blend in with dead leaves.
Diet: Flying insects like flies, beetles, moths, leafhoppers, mosquitoes and cicadas. They like bigger bugs.
Behavior: Often the first to emerge after sunset, feeding early in the evening, and occasionally on the ground. In winter, males may emerge from hibernation to feed even in the daytime.
Breeding: Breed in fall. Delayed fertilization leads to 3 to 5 young in late May or early June. Babies begin to fly at 4 to 6 weeks old.
Migration: In northern areas of their range, they migrate south with cold fronts. Southern bats hibernate.
Threats: Bats with the 2nd greatest mortality from wind turbines. Often killed by hawks, owls, blue jays, crows, cars, and tall buildings. Asymptomatic carrier of White-Nose Syndrome.
Conservation Status: International Union for Conservation of Nature Status “Least Concern.” Abundant throughout their range, but evidence of decline in the last 100 years.
Evening Bat Nycticelus humeralis
Size: 3.4” to 4.1,” weighing .02–.05 oz
Wingspan: 10.2”to 11”
Appearance: Small, dark brown, with black ears and wings. Broad muzzled, fur is dark at base & grayish at tips. Tail has fur only on the upper side at the base. Often mistaken for juvenile Big Brown bats.
Habitat: Eastern deciduous forests, east coast west to Nebraska and south through East Texas to Mexico. Commonly roosts in tree hollows, behind loose bark, and in tree crevices. Rarely enters caves but will swarm with cave bats outside cave entrances. Also likes old wooden buildings.
Diet: Insects, particularly cucumber beetles, June bugs, Japanese beetles, flying ants & moths.
Behavior: Feeds once per night, high up early in the evening, lower after dark. Maternal colonies of 25 to 950 mothers and babies will share nursing and foraging. Males leave the nest early; females remain and forage with their mothers until fall.
Breeding: Breed in fall. Delayed fertilization typically results in 2 to 3 pups in late May or early June. Babies can fly at 20 days old, and wean by 9 weeks.
Migration: Believed to migrate south in fall, but little is known about this.
Threats: Loss of old-growth trees and old wooden buildings. Artificial roosts may help the species.
Conservation Status: Not widely studied, except in Indiana, where they are considered endangered. US Fish & Wildlife does not list the evening bat as a species of concern.
Hoary Bat Lasiurus cinereus
Size: 5” to 6” Weight: 1 to 1.3 ounces (females are 40% heavier)
Wingspan: 13” to 16”
Appearance: Large, distinctively marked bat with long, narrow wings and large ears. Long, soft, dark brown fur with white tips, giving it a hoary appearance. Yellowish-brown collar under chin and fully furred tail.
Habitat: Diverse woodlands with deciduous and coniferous forests, agricultural edges, and hunts over open areas and water. Occasionally found in caves with other bats and in Spanish moss in edge habitats. Will also use bird nests in hollow trees.
Diet: Mainly moths and beetles, occasionally mosquitoes when in abundance.
Behavior: Territorial—will return to the same area to feed every night, flying as far as 24 miles. Leave the roost soon after dusk, making 2 foraging trips per night. Feed lower in open areas, will feed above the canopy when prey is abundant. Males roost in conifers, females and pups roost in deciduous trees.
Breeding: Mates in August, gives birth in June (delayed implantation) to twins or up to 4 pups. Babies can hang alone within 7 days, can fly in 30 days, and be fully weaned in 7 weeks.
Migration: Winter in Central America and coastal areas of the United States. Range includes northern Canada through Argentina—the widest range of any New World bat.
Threats: 40% of bats killed by wind turbines are hoary bats.
Conservation Status: Little is known, but only the Hawaiian subspecies is considered threatened.
Seminole Bat Lasiurus seminolus
Size: 4.5” Weight: 8 to 15 grams (0.529 ounce)
Wingspan: 11 to 13″
Appearance: Medium-sized bat with deep mahogany fur often frosted at tips giving it a maroon hue, with white patches on wrists and shoulders.
Habitat: Mixed deciduous forests with Spanish moss. Little is known about their habits. They will roost in loose bark in extreme weather. They like oak, hickory, and pine forests, agricultural edges near open areas, and wetlands.
Diet: Leafhoppers, flies, beetles, and will glean ants and other insects from foliage. They feed high, above the canopy, and as low as 1 meter above ground. They generally feed from 8 pm to midnight, and again about 2 am for 30 minutes.
Behavior: They go after prey attracted to street lamps and outdoor lighting. Also feeds in multispecies groups. They rear their young among tree foliage and Spanish moss.
Breeding: They mate late fall, usually in flight, and give birth in late May or early June to 1 to 4 pups.
Migration: Not known to migrate or hibernate, but will fall into torpor during cold spells.
Threats: Very little data exists, but professional moss gatherers report disturbing maternal colonies. Predators that eat eastern red bats also eat seminole bats.
Conservation Status: Status and population trends are unknown. More research on roosting habits is needed, as is education of moss gatherers.
Tricolored Bat Perimyotis subflavus
Size: 2.75” to 3.75” Weight: 4 to 8 grams
Wingspan: 8 to 10″
Appearance: Very small yellowish-brown bat with tricolor fur, black at the base, very light brown, with darker tip. Among the smallest species of bat, they can live up to 15 years in the wild.
Habitat: Oak, maple, and cottonwood forests and forest edges near water and open areas. They spend 6 to 9 months of the year hibernating in caves, mines, and abandoned buildings, clinging to walls and ceilings. Where mines and caves are sparse, they will hibernate in culverts. Males live alone in the summer, while females form small maternal colonies with their young and other females in tree cavities and rock crevices. In northern areas, they have also been known to roost in lichen.
Diet: leafhoppers, ground beetles, flies, moths, ants, cicadas.
Behavior: Usually the first bats to emerge in the evening, they do two forages each night, right around sunset and again about midnight. They can eat 1 insect every 2 seconds. They exhibit high site fidelity, returning to roost and feed in the same locations.
Breeding: They mate in fall. Females store sperm all winter until they ovulate once they emerge from hibernation in the spring. Two babies are born hairless and blind between May and July, but develop rapidly, flying within 3 weeks and weaning in 4.
Migration: They may migrate no more than 30 to 50 miles between nursery and hibernation sites. They hibernate early—late September/October—and emerge late in the spring.
Threats: Highly susceptible to White-Nose Syndrome, which is rapidly spreading since its arrival in the United States in 2006. Preyed upon by leopard frogs, birds, raccoons, skunks, and snakes. One of 2 species implicated in cases of human rabies transmitted by bats.
Conservation Status: While not yet officially listed, the tricolored bat meets the definition of endangered under the Endangered Species Act of 1973 and has been under consideration for final listing since October 2022.
Samra Bufkins, is co-project manager of the Acoustic Bat Monitoring project and a Texas Master Naturalist with the Elm Fork chapter.