WSB study: Acoustic lures help net elusive bats

Bat researchers have trouble using nets to catch species that forage in open spaces and fly too high, out of reach of traditional netting methods. But researchers seeking to catch endangered Florida bonneted bats (Eumops floridanus) found they could lure the bats to their nets by playing recordings of the social calls the species uses to communicate.

“The acoustic lure was an effective method to increase the capture success of Florida bonneted bats,” said Elizabeth Braun de Torrez, first author on the study on the technique published in the June issue of the Wildlife Society Bulletin. “This is significant because prior to our study, only one bonneted bat had ever been captured in a net away from a known roosting location.”

Braun de Torrez, a post-doctoral research associate with the University of Florida’s Department of Wildlife Ecology and Conservation, and her team spent much of 2015 futilely trying to catch the bats, which would simply fly over their nets. Hearing the bats chattering overhead, the researchers wondered if the animals were attracted to one another’s calls. They designed an experiment to capture them using an ultrasonic speaker that broadcasted the species’ social calls. Similar acoustic lures have been tested on other bat species with varying results.

To create the lure, Braun de Torrez and her colleagues recorded Florida bonneted bat vocalizations at two roosting locations and picked out sounds resembling social calls. Then they tested it at two sites each in three conservation areas within the bat’s range in southern Florida — Fakahatchee Strand Preserve State Park, Florida Panther National Wildlife Refuge and Fred C. Babcock-Cecil M. Webb Wildlife Management Area. At each site, they set up four pairs of large, stacked mist nets, which biologists commonly use to trap bats. They played the recorded calls at two of the nets the first night of sampling and switched the lures to the other two nets the following night.

“We captured 15 Florida bonneted bats, and all of them were in nets with the acoustic lure,” Braun de Torrez said. “We captured bats on nine of 12 nights of the experiment and in all three conservation areas. The lure was successful across multiple nights and locations.”

The scientists plan to investigate the social meanings of their recordings to better understand why one lure worked more effectively and why they trapped more males than females in hopes of improving the tool.

The lure could facilitate more studies for the protection of the species, whose small populations are increasingly threatened by habitat loss due to development in their very limited native range in southern Florida, Braun de Torrez said.

“If we can capture a Florida bonneted bat, we’re able to identify its sex, reproductive condition and collect guano or tissue samples for genetic analysis,” she said. “We can also put radio transmitters on them, a way of tracking bats to new roosting locations, which is extremely important for the conservation of these bats.”

This is the first time mist netting with an acoustic lure has been tested on Mollosidae, bats that typically fly high and forage in open spaces, Braun de Torrez said, setting the stage for further research on other species in this family.