URBANA, Ill. (U.S.A.) — Finding bats in the attic or under roof tiles is no homeowner’s idea of fun. But Florida’s endangered bonneted bats have few natural options left. With a dwindling number of large, old trees with cavities — their preferred habitat — and exotic species competing for what’s left, many bonneted bats have moved into homes, leading to panicked humans and calls to professionals who can oust the squatters.

Florida’s land managers have been working for years to lure bonneted bats away from homes and towards artificial roosts, with varying long-term success. For other bat species, artificial roosts fail to protect bats from temperature extremes, and bats move out or, sadly, perish. Now, researchers from the University of Illinois Urbana-Champaign, along with partners at the U.S. Army Corps of Engineers and the Florida Fish and Wildlife Conservation Commission, have shown that bonneted bats can be lured to and inhabit safer bat boxes. Their findings are published in the Journal of Mammalogy.

“Not all artificial roosts are created equal. Previous work in our lab has shown some bat boxes can be very dangerous for bats because they can’t properly buffer against temperature swings. But this study demonstrates that bonneted bats will move into safer structures that mimic their natural roosts and maintain a stable thermal environment,” said the study’s senior author Joy O’Keefe, associate professor in the Department of Natural Resources and Environmental Sciences (NRES) and Illinois Extension specialist; both units are part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.

O’Keefe and the team set up three types of artificial roosts at six points in a natural area in southern Florida. The roosts included a flat-faced box with a single chamber for bats (the most commonly used design); a four-chambered “rocket box” design that allows bats to move around inside; and a rocket box with an external water jacket that buffers temperature change. They also broadcast recordings of bonneted bat echolocation calls — acoustic lures — from half of the box clusters. Then, for 18 months, they waited, checking the boxes weekly.

For the majority of that time, nothing. No bonneted bats set up shop in the boxes, though acoustic recorders detected them flying nearby each spring. Finally, after 16 months, a single male settled into one of the water-jacket rocket boxes. And 13 months after the conclusion of the study, a harem colony was established in the same box.

Although the results were modest, the team took away two important lessons.

“We know from our previous studies on microclimates in artificial roosts that the external water jacket provides much safer temperatures for these bats,” said Reed Crawford, a postdoctoral researcher in NRES and lead author on the article. “Now we know they will use that box, so that could be a better alternative to the current artificial roost design that's being installed out there. And it's fairly straightforward to build.”

Crawford also emphasized the importance of long-term follow-up observations. “When working with endangered species, long-term projects are very important, whereas studies like ours often amount to only one or two field seasons. But it took a long time to see results. We were fortunate to have our partners at the Florida Fish and Wildlife Conservation Commission following up three and four years post-deployment.”

At last count, 17 individuals were counted in the water jacket box, including females that had been using chamber boxes in an adjacent natural area. Considering a 2022 estimate of the entire population of Florida bonneted bats was in the low hundreds to low thousands, Crawford said, “that's actually a pretty good chunk of those bats moving into our box.”

Because only one box ended up being occupied, the researchers didn’t think the acoustic lures had much of an effect. Indeed, they pointed to the possibility that the calls could have dissuaded bats from entering the boxes, for example by signaling that the boxes were already occupied or that an aggressive male was in the area. Instead, they think just putting boxes up and waiting is the best approach.

“There’s a lot of complexity to their calls, and we don’t necessarily know what they’re saying. It will require a lot of additional behavioral work to figure out what specific call types are important for them, and what those types of calls mean,” Crawford said.

In addition to providing a safe thermal environment for bats, the rocket boxes held up against the changing Florida climate, including increasingly intense storms.

“Between June and September of 2022, that one male bonneted bat was using our water jacket box basically every day. Then Hurricane Ian hit, a major Category 5 storm,” O’Keefe said. “When our field technician and co-author, Ellen Pierce, went back a week later, the bat was in the box. And the boxes were still standing just fine.”

The study, “Calling home: Do acoustic lures and novel roosts attract the rare Florida Bonneted Bat (Eumops floridanus)?” is published in the Journal of Mammalogy [DOI:10.1093/jmammal/gyag013]. Authors include Reed D. Crawford, Patrick J. Wolff, Ellen C. Pierce, Elizabeth C. Braun de Torrez, Roxanne D. Pourshoushtari, and Joy M. O’Keefe.

Research in the College of ACES is made possible in part by Hatch funding from USDA’s National Institute of Food and Agriculture. This study was also supported by the National Defense Center for Energy and Environment [federal award ID #: W9132T2020007].

O'Keefe is also affiliated with the Illinois Natural History Survey, part of the Prairie Research Institute at Illinois.