Wildfire, Depredation, and Synergistic Management Challenges Contribute to the Decline of a Significant Population of Florida Box Turtles (Terrapene bauri)

Abstract

The Florida box turtle (Terrapene bauri) population on Egmont Key National Wildlife Refuge, Florida, was the subject of long-term ecological studies from 1991 to 2006. The Egmont Key population was relatively large and stable compared with other populations of Terrapene spp. that were studied for multiple decades, with an increasing population trend and approximately 1500 turtles in 2002. We conducted a reassessment of the population in 2017–2018, and we specifically evaluated the effects of a 26.1-ha wildfire that occurred in July 2016. In March 2017 we implemented randomized, time-constrained surveys, which detected an average of 38.5 dead box turtles per ha, from which we extrapolate approximately 1005 (95% CI = 786–1223) detectable, dead box turtles across the extent of the 2016 wildfire. Of 259 dead box turtles found during this survey, a minimum of 65 were judged to have died coincident with the 2016 wildfire. Another 43 turtles, apparently killed by predators (most likely raccoons, Procyon lotor), were found in burned and unburned areas. One hundred forty-eight were too badly burned or deteriorated to estimate the likely cause of death. Additional surveys in 2017 and 2018 further assessed the condition of the remaining box turtle population. Between March 2017 and March 2018 we detected a total of 347 box turtles, of which 32 were alive and 315 were dead. We estimated the population to consist of 65.5 (95% CI = 41.6–149.1) live turtles, indicative of a > 95% population decline since the early 2000s. Our results illustrate the need for populations of nonlisted, yet vulnerable, species to be prioritized on protected sites, and monitored to detect the effects of stochastic, chronic, and synergistic sources of mortality.