Species Distribution Modeling for Bog Turtles (Glyptemys muhlenbergii) in North Carolina

Abstract

The bog turtle (Glyptemys muhlenbergii) is the smallest turtle species in North America and is listed as a threatened species under the federal Endangered Species Act. Accurate detection of its specialized wetland habitat and subsequent tagging of individuals for monitoring purposes is critical for improving conservation efforts with this species. Parts of the Piedmont region in North Carolina have historically served as habitat for bog turtles, but few populations are now known to occur there. Increases in residential development, agricultural land use, and the draining of wetland areas over the past several decades have likely contributed to their current extirpation from this part of the state. Most wildlife managers no longer survey for bog turtles in most of the Piedmont as efforts are both time and cost prohibitive, and funding generally all allocated for work in counties where they have a better chance of locating bog turtles during a given survey event. Several managers acknowledge that there may still be bog turtles living in the Piedmont, but because of present limitations, there is currently no conservation plan for them. GIS and predictive modeling were used as a low-cost method for locating potential sites within four North Carolina counties that exhibit suitable habitat characteristics for bog turtles. Such predictions may prove useful in documenting new occurrences of bog turtles in both the Piedmont counties of Iredell, Davie, and Davidson, as well as in the higher quality bog turtle habitat regions of Wilkes County. The Maxent distribution model was used as it is capable of producing accurate habitat predictions for species with small sample sizes. A total of 28 areas with species presence and 16 different environmental variables were used in the analysis. The model returned several sites within Wilkes County exhibiting higher levels of predicted suitability, and a smaller number of sites within Iredell County with moderate levels of suitability. The predicted sites in Iredell County were previously unknown to wildlife managers, and may help to direct future survey work in those locations. If these model predictions can be translated to positive detection of turtles in the field, spatial modeling work of this kind may begin to play a larger role in the conservation efforts for the species.