Leyna Stemle (University of Miami) and Betsie Rothermel (Archbold Biological Station)
Learn about ongoing research on gopher tortoise movement happening at Archbold Biological Station in Florida.
Knowing the movement patterns and habitat preferences of gopher tortoises during different life stages is critical for determining the types and amount of habitat needed to support populations of this threatened species. However, conservation planning for gopher tortoises is currently hindered by limited knowledge of the ecology of younger age classes. For example, only three studies have estimated home-range sizes for juvenile or subadult gopher tortoises (tortoises roughly 1-7 years). Those studies estimated that immature tortoises use relatively small areas on the order of 0.05 – 0.52 hectares (ha).1-3 Other studies of juveniles have found that most of their daily movements are within 25 meters (m) of their burrow.3-6
During summer 2019, Leyna Stemle, a PhD Candidate at University of Miami, led a collaborative project with the Archbold Herpetology Program to track the movements of six immature gopher tortoises at Archbold Biological Station in south-central Florida. This project was the first to use GPS tags to quantify space use of 3- to 7-year-old gopher tortoises. The short battery life of the GPS tags meant we could only track the six juveniles for a maximum of 40 days. Surprisingly, the resulting home range estimates averaged 0.38–1.46 ha (Fig. 1), much larger than most previously reported annual home ranges derived from manual telemetry data. Likewise, the GPS tag locations revealed that tortoises frequently moved 43–79 m in a single day! While it may be that juvenile tortoises at Archbold are unusually wide-ranging, we think it more likely that the continuous, hands-off nature of remote tracking provides a more accurate picture of the true scale of their movements. For more about this project, check out the full article in the latest issue of the Journal of Herpetology (June 2022).
We have greatly expanded our juvenile tortoise tracking efforts over the past year with support from Disney Conservation Fund. Since March 2021, we have radio-tagged 29 juvenile tortoises to compare movements and growth rates in native sandhill versus open, ruderal habitats. Despite the known limitations of manual telemetry, traditional VHF radio tags have the advantages of being much smaller and having a longer battery life than commercially available GPS tags. This research is benefitting from further collaboration between Archbold and the University of Miami Conservation Ecology Lab (Fig. 2) and is documenting further unprecedented movements of young (3- to 5-year-old) gopher tortoises (Fig. 3).
The movements shown in Figure 3 were surprising for several reasons. First, during the same period in the previous year (March-July 2021), the farthest we saw any of these individuals away from their burrow was ~ 200 m. Next, these movements occurred rapidly and within a few weeks of each other during the late dry season. This makes us think they may have been triggered by weather or food limitation. Tortoise #1370 moved a straight-line distance of ~1.24 kilometers (km) in < 3 days. Notably, the movements by tortoises 1370 and 1740 were substantially longer than the longest published movement for an immature gopher tortoise (744 m in 4 days by a subadult2).
Another intriguing aspect of these observations is that these juveniles moved out of more open, restored sandhill into unburned sandhill, after living in restored sandhill for over a year. All three moved in the same direction (westward and downhill) through areas of long-unburned, overgrown sandhill, taking shelter in brush piles or dense vegetation or hiding at the base of palmettos under leaf litter. Two tortoises successfully crossed a 55-mph road – and #1740 (15.2 cm CL) repeated this feat on its return trip!
These results may represent some of the first recorded paths of immature, non-headstarted tortoises dispersing, or attempting to disperse (headstarted tortoises are raised in a protected environment during their vulnerable first months/years ). Information on such long-distance movements can be incorporated into estimates of minimum area requirements that are useful for conservation planning. Additionally, determining the age range of dispersers, the habitats they move through, and how far they can go is valuable for understanding landscape-scale connectivity and gene flow between gopher tortoise populations.
1Butler JA, Bowman RD, Hull TW, Sowell S (1995) Movements and home range of hatchling and yearling Gopher Tortoises, Gopherus polyphemus. Chelonian Cons Biol 1:173–180
2Diemer JE (1992) Home range and movements of the tortoise Gopherus polyphemus in northern Florida. J Herpetol 26:281-289.
3Wilson DS, Mushinsky HR, McCoyED (1994) Home range, activity, and burrow use of juvenile Gopher Tortoises (Gopherus polyphemus) in a central Florida population. In: Biology of North American Tortoises, Fish and Wildlife Research, U.S. Department of the Interior.
4McRae WA, Landers JL, Garner JA (1981) Movement patterns and home range of the Gopher Tortoise. American Midland Nat 106:165–179.
5Epperson DM, Heise CD (2003) Nesting and hatchling ecology of Gopher Tortoises (Gopherus polyphemus) in southern Mississippi. J Herpetol 37:315–324.
6Mushinsky HR, Stilson TA, McCoy ED (2003) Diet and dietary preference of the juvenile gopher tortoise (Gopherus polyphemus). Herpetologica 59:475–483.