Data Associated with "Effects of vegetation structure and soils on gopher tortoise (Gopherus polyphemus) nest-site selection in southwest Georgia"

Early life is a period of high mortality for many turtle species, so understanding how turtles select nest sites may be important in our ability to manage declining populations and species. In gopher tortoises (Gopherus polyphemus), nest-site selection in relation to vegetation and soil characteristics is poorly understood. From mid-May to mid-July 2022 and 2023, we investigated aspects of gopher tortoise nest-site selection within longleaf pine habitat in southwestern Georgia. We conducted repeated searches at burrows to locate nests, and at each nest (n=132) we collected soil samples and measured canopy and understory cover. We collected the same data at an equal number of burrows without nests. Using multiple logistic regression, we created a suite of six biologically relevant candidate models (combinations of percent clay in soil and canopy and understory vegetation cover) and compared models with Akaike’s Information Criterion corrected for small sample sizes. The top three models identified canopy cover and understory vegetation cover as meaningful predictors of nest presence at burrows, with tortoises in our sites nesting at burrows with lower understory and canopy cover than available burrows. Furthermore, there was an interaction between the effects of understory vegetation and canopy cover, where the effect of understory cover decreased as canopy cover increased. This result suggests that the vegetation effect may be primarily driven by an avoidance of shade, whereby nests laid in burrows with high canopy cover were so shaded that understory vegetation had a weaker influence on nest-site selection. We did not observe an effect of percent clay in soils on nest-site selection, as has been observed at other sites. This may indicate that nest-site selection differs across the species’ range. Our results suggest that maintaining habitats with very open or patchy overstories may be most important for providing preferred nest sites for gopher tortoises in this part of their range.