Florida Bonneted Bat Roost Selection: Implications for Conservation

By Elizabeth Braun de Torrez

The Florida bonneted bat (Eumpos floridanus), which occurs only in Florida, is federally endangered and extremely rare. These bats can traverse extensive areas to forage but their distribution may be restricted by the availability and security of roosting sites. However, we know very little about what types of natural roosts the bats use or whether tree roosts are readily available across the landscape. In our current study, we are working to identify and characterize previously unknown roost locations in conservation areas across southwest Florida. This information will allow us to protect existing roost structures and to develop guidelines for conserving or enhancing roosting habitat for this species.

Building upon research started with the University of Florida, we are using a combination of acoustic surveys, mist netting and radio-telemetry. Florida bonneted bats are notoriously difficult to capture in mist nets due to their high-altitude flight, and prior to our recent research this species had only been captured once away from known roost sites. Using a technique we developed involving an acoustic lure that broadcasts conspecific social calls to attract this species to nets, we now have the ability to capture free-flying individuals, attach radio-transmitters and track them back to unknown roost sites using radio-telemetry.

Florida bonneted bat with VHF radio-transmitter attached to break-away collar.

To capture bats, we erect a triple high mist net system (9 m high) coupled with an acoustic lure. Upon capture, we identify the individual’s species, sex, reproductive status and take standard measurements (e.g., mass, forearm length). We also collect a 4mm wing biopsy and guano sample for genetic and diet analysis. For adult, non-pregnant Florida bonneted bats, we secure a VHF radio-transmitter attached to a break-away collar and track the bats to roost structures using a combination of aerial and ground-based radio-telemetry. Due to the suspected distance that these bats are capable of flying between foraging areas and roost sites (ca. 25 miles) and the challenges of navigating throughout the south Florida terrain, aerial telemetry is essential to locate roost sites!

Once we locate a potential roost, we verify occupancy and colony size by counting the number of Florida bonneted bats that emerge around dusk, and measure characteristics of the roost tree (e.g. height, size and orientation of roost opening). We also measure characteristics of the surrounding vegetation (e.g., tree density, canopy height, canopy cover) in a plot around the roost tree and at four random tree plots.

Royal palm snag in Fakahatchee Strand Preserve State Park containing 80 Florida bonneted bats. This is the largest known colony for this species.

We are in the process of compiling data from natural roosts that we have located, in conjunction with our research partners, over the last several years. In total, we have located 17 roost trees, with 5 new roosts located in 2018. The roosts include enlarged woodpecker cavities, cavities formed from decay, and spaces under loose bark, and they occur in live and dead long leaf pine, slash pine, royal palm and cypress trees. Colony sizes range from 1 individual to a new record of 80 bats in a recently discovered royal palm roost in Fakahatchee Strand Preserve State Park in May 2018. Of these 17 roost trees, 6 have since been damaged or destroyed by fire or hurricanes. Ultimately, we will use the data collected on new Florida bonneted bat roost structures to examine patterns of roost site selection relative to a variety of local and landscape-scale variables, and make appropriate habitat management recommendations.