SREL Reprint #3326

Overwintering ecology of juvenile Gopher Tortoises (Gopherus polyphemus)

Bess B. Harris1,2,5, Terry M. Norton3,4, Nathan P. Nibbelink2, and Tracey D. Tuberville1

1University of Georgia’s Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802, USA
2Daniel B. Warnell School of Forestry and Natural Resources, 180 E Green Street,
University of Georgia, Athens, Georgia 30602, USA
3Jekyll Island Authority’s Georgia Sea Turtle Center, 214 Stable Road, Jekyll Island, Georgia 31527, USA
4St. Catherines Island Foundation, 182 Camellia Road, Midway, Georgia 31320, USA
5Current affiliation: Florida Fish and Wildlife Conservation Commission, Lovett E. Williams, Jr.
Wildlife Research Laboratory, 1105 SW Williston Road, Gainesville, Florida 32641, USA

Abstract: The Gopher Tortoise (Gopherus polyphemus) is a large terrestrial turtle that excavates and occupies extensive burrows, which protect individuals from predators and temperature extremes. Individuals can thermoregulate behaviorally by adjusting their position inside the burrow and through surface activity, even in winter when they are thought to be relatively inactive. Much of what is known about the overwintering behavior of Gopher Tortoises is based on adults; however, the ecology of juveniles may differ due to their smaller body size and higher surface area to volume ratio. We investigated the overwintering ecology of 11 juvenile Gopher Tortoises on St. Catherines Island, Georgia using externally attached temperature loggers. Temperatures experienced by tortoises were compared to burrow and surface air temperatures collected at the same site, allowing us to infer surface activity of individuals. We examined the onset, termination, and duration of overwintering and occurrences of juvenile surface activity during the overwinter period. Tortoises initiated overwintering over a 48-d period (median date of 14 November) and terminated overwintering over a 32-d period (median date of 8 April). Mean overwintering duration was 130 ± 7 d (1 SE). Individuals emerged on 2–22 d during the 2012–2013 winter. Mean temperature experienced by overwintering tortoises was 17.9 ± 0.02°C (range 11.5–38.5°C) and the minimum surface air temperature when a juvenile tortoise emerged from its burrow to bask was 15.8°C. Timing of overwintering in juvenile Gopher Tortoises is similar to that reported for adult tortoises from similar latitudes. However, juveniles are active more frequently on the surface during the winter and emerge from burrows at lower air temperatures than has been reported for adults.

Keywords: activity; dormancy; Georgia; reptile; temperature

SREL Reprint #3326

Harris, B. B., T. M. Norton, N. P. Nibbelink, and T. D. Tuberville. 2015. Overwintering ecology of juvenile Gopher Tortoises (Gopherus polyphemus). Herpetological Conservation and Biology 10(2): 645-653.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).