The Orianne Indigo Snake Preserve (OISP) contains just over 2,500 acres of protected lands located in the heart of southern Georgia. The property contains a mix of sandhills, small creeks and wetlands, and a large floodplain that backs up to the Ocmulgee River. An impressive 75 species of amphibians and reptiles have been documented on the property, and it provides a home to several rare or imperiled species, including the Eastern Indigo Snake, Gopher Tortoise, and Tiger Salamander. The OISP is also important because it serves as The Orianne Society’s home base in southern Georgia, housing all of our land management and sampling equipment. Over the last 10 years, an impressive amount of management has been conducted on the property. Tree planting, thinning, prescribed fire, and ground cover restoration have gone a long way to restoring the Longleaf Pine forests to their former glory.
One of the special things about the OISP is that it is home to a large Gopher Tortoise population. In combination with the adjacent Horse Creek WMA, the tortoises on the OISP represent one of Georgia’s few remaining viable tortoise populations (those with at least 250 individuals). This population has now been protected for many years, although threats remain even within protected lands (e.g., roads, disease, and predation by feral dogs). Individuals have certainly benefited from ongoing management activities, which, if nothing else, have increased the total area of land suitable for tortoises on the OISP. However, an important part of the ongoing conservation work is making sure that the population is stable or increasing through time and is not being negatively impacted by outside threats.
To do this, we periodically survey the Gopher Tortoise population on the OISP using Line Transect Distance Surveys (LTDS). LTDS are the most common methodology used to survey tortoise populations in the southeast (see Smith and Howze 2016 for a detailed description). This methodology involves walking straight-line transects through available tortoise habitat with 1–3 observers searching for tortoise burrows. Once a burrow is identified, a burrow camera is used to determine whether or not the burrow is occupied by a tortoise. The distance that all occupied burrows are from the sampling transect can then be used to estimate the population size for the sampling area. Completing LTDS, especially during the Georgia summer, makes for long hot days in the field but provides critical information about the tortoise population on the OISP.
During 2020, we completed our third complete survey of the OISP’s tortoise population since 2011. We walked approximately 63.4 km of tortoise transects, scoping a total of 747 Gopher Tortoise burrows. We were able to determine the occupancy status of 718 (96%) of these burrows (deep sand, winding burrows, or other obstructions sometimes prevent the camera from reaching the bottom of the burrow). A total of 171 (24%) burrows were occupied by at least one tortoise and several burrows contained multiple tortoises. Population estimates for the Lower, Middle, and Upper Tracts of the OISP were 74, 180, and 52 tortoises, respectively. These results are consistent with the surveys that have been completed in previous years, indicating that the tortoise population on the OISP has remained stable through time. We will continue to monitor this population in the future and will likely expand surveys into new areas as the habitat improves through continued land management.
Smith, L.L., and J.M. Howze. 2016. Gopher Tortoise line transect distance: Sampling workbook. Joseph W. Jones Ecological Research Center. 35 pp.