The gopher frog Lithobates capito is one of the most terrestrial frogs in the southeastern U.S. and often inhabits gopher tortoise burrows Gopherus polyphemus outside of the breeding season. Gopher frog populations have declined, and the species is under review for listing as threatened or endangered under the U.S. Endangered Species Act. Much of our knowledge on the status of gopher frogs is based on detections of larvae at breeding wetlands, which can be challenging due to environmental variability and provides no information on the terrestrial life stages of the species. Therefore, an alternative method is called for. We recorded observations of gopher frogs during gopher tortoise surveys at four conservation lands in Florida and used line transect distance sampling to estimate frog abundance. We also recorded burrow size, incidence of frog co-occupancy with tortoises, and distance from frog-occupied burrows to breeding wetlands. We observed 274 gopher frogs in 1,097 tortoise burrows at the four sites. The proportion of burrows occupied by gopher frogs among sites ranged from 0.17 to 0.25. Gopher frog abundance in tortoise burrows was 742 (512–1,076 95% CL) at Etoniah Creek State Forest, 465 (352–615) at Ft. White Wildlife Environmental Area, 411(283–595) at Mike Roess Gold Head Branch State Park, and 134 (97–186) at Watermelon Pond Wildlife Environmental Area. We observed up to four frogs in a single burrow. The proportion of frogs detected in burrows occupied by a gopher tortoise ranged from 0.46 to 0.79 among sites, and overall, gopher frogs preferred burrows occupied by tortoises over unoccupied burrows (χ 2 = 15.875, df=3, p = 0.001). Gopher frogs used burrows from 7 to 43 cm in width; mean width of frog-occupied burrows did not differ from that of unoccupied burrows ( F 1,3 = 0.0492, p = 0.8245). Distance from frog-occupied tortoise burrows to the nearest breeding wetland ranged from 141 to 3,402 m. Our data on gopher frogs collected in conjunction with gopher tortoise monitoring efforts using line transect distance sampling and burrow cameras provided novel information on frog abundance in their terrestrial habitat and required no additional effort. However, the extent to which frogs use tortoise burrows relative to other available refuges (small mammal burrows, stumps, or other structures) is unknown, thus our estimates should be considered conservative. We suggest that terrestrial abundance estimates for gopher frogs can complement efforts to monitor breeding activity to provide a more comprehensive means of monitoring population trends in this cryptic species.

Gopher tortoise Gopherus polyphemus populations have declined by as much as 80% over the past century, primarily as a result of habitat loss. In 2006, the eastern population of the gopher tortoise was petitioned for federal listing as threatened. In response, a Candidate Conservation Agreement was developed for the gopher tortoise. A Candidate Conservation Agreement is a voluntary agreement between the U.S. Fish and Wildlife Service and other interested parties to address the conservation needs of a species before it becomes federally listed and to enact measures to preclude the need to list the species. The gopher tortoise Candidate Conservation Agreement identified an assessment of the status of populations on protected lands as a priority and line transect distance sampling (LTDS) was adopted as the standardized survey methodology. Surveys with LTDS rely on detection of gopher tortoise burrows because tortoises are fossorial. However, gopher tortoise burrows vary greatly in size and small burrows of juveniles are rarely detected. Although LTDS is statistically robust and allows for imperfect detection, few studies have examined how detection varies with tortoise burrow size and whether habitat structure may influence detection of gopher tortoise burrows. Both factors could affect the accuracy of population estimates using LTDS and interpretation of demographic parameters needed for the Candidate Conservation Agreement. Therefore, we conducted surveys for burrows using LTDS before (28 March–13 April 2016) and after (9–18 May 2016) a prescribed burn, which reduced vegetation cover. We detected significantly more burrows (P < 0.001, n = 651) of all sizes after the burn, and the burrow abundance estimate was 64% higher postburn. Our study showed that conducting gopher tortoise surveys after a prescribed burn increased detections and provided a more accurate population estimate. We therefore recommend conducting surveys immediately after a burn. However, varying burn cycles on large sites may make it difficult to survey following a prescribed burn and because the effects of a burn on habitat structure may vary within a site, methods to account for variation in detection due to habitat structure are needed. Population estimates for gopher tortoises using LTDS that do not account for variation in detection due to habitat structure likely underestimate population size.

Gopher tortoises (Gopherus polyphemus) occur in open-canopy pine habitat on well-drained soils in the southeastern United States, where they construct burrows that offer protection from thermal extremes, fire, and predators. Gopher tortoise populations have declined over the past 50 y, primarily as a result of habitat loss and degradation. Southeastern pine forests require active management with prescribed fire, mechanical thinning, or removal of hardwoods to maintain suitable habitat for gopher tortoises. In addition, many pine forests in the Southeast that support gopher tortoise populations are managed for multiple uses including intensive silviculture. Heavy equipment associated with these activities used in proximity to gopher tortoise burrows can cause them to collapse, potentially causing harm to tortoises or other imperiled organisms that use their burrows. Hence, there is a need for practical guidelines for use of heavy equipment for timber harvest, management, and other activities around gopher tortoise burrows to minimize risk to tortoises. We conducted a field study to determine the distance at which heavy equipment caused gopher tortoise burrows to collapse using a feller buncher, rubber-tire front-end loader, and an agricultural tractor with a tree-mower attachment in sandy clay loam (15 burrows) and undifferentiated deep sand (15 burrows) soils at a site in southwestern Georgia. All burrows were confirmed to be unoccupied by tortoises or other vertebrate commensal species using a camera scope before collapse. The greatest mean distance to collapse across all vehicles tested in sandy clay loam and undifferentiated deep sand was 2.19 ± 0.56 m and the maximum distance to collapse was 3 m. Given the variation in collapse distance, we recommend a buffer that extends 4 m in radius from the entrance of the gopher tortoise burrow to minimize risk of collapse from heavy equipment.

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