Effects of Vegetation Structure and Artificial Nesting Habitats on Hatchling Sex Determination and Nest Survival of Diamondback Terrapins

It is often the case that multiple factors contribute to wildlife population declines such that management will require simultaneous, integrated interventions to stabilize and recover populations. Diamondback terrapins Malaclemys terrapin are a species of high conservation priority, and local populations can be threatened by multiple factors, including bycatch in commercial and recreational crab pots, vehicle strikes on coastal roads, nest depredation from subsidized and introduced predators, and terrestrial habitat alteration. Mitigation of just one of these factors will often be insufficient for recovering at-risk populations; thus, information to manage multiple threats is needed. We measured the effects of natural vegetation structure and constructed (artificial) nesting habitat on hatchling sex ratios and nest depredation for a declining terrapin population on Jekyll Island, Georgia. Nest temperatures were highest on constructed nesting mounds, intermediate in open grass areas, and coolest under the shrub-dominated hedgerows. Higher nest temperatures led to shorter incubation times for nests on mounds and open habitat, such that all surviving nests on nesting mounds and open areas produced female hatchlings. In contrast, surviving nests under hedge produced 85% male hatchlings. Raccoon Procyon lotor predation rates of simulated (chicken egg) nests were highest on nesting mounds (95.3%), followed by hedge (84.4%) and open habitats (45.2%). Our results demonstrate that vegetation management can positively affect both production of female hatchlings and nest survival. Artificial nest mounds were successful at producing female hatchlings, but we documented high predation of simulated (chicken egg) nests despite structures to exclude predators. Further modifications to nest boxes atop constructed nesting mounds are needed for these devices to effectively contribute to population management. We suggest the relatively low cost and maintenance associated with removing shrubs and trees can be a viable strategy to manage large areas of nesting habitat for the increased production of female turtles, and to reduce the impacts of subsidized predators.