Nest-site choice and fidelity in tuatara on Stephens Island, New Zealand

Nest-site microhabitat influences hatching success, hatchling phenotype and offspring sex in reptiles with temperature-dependent sex determination (TSD). How females assess environmental features at potential nest sites, and then use such features in predicting the future incubation regime of the site, is integral to understanding how nest-site choice affects offspring fitness and ultimately female reproductive success. Tuatara Sphenodon punctatus are colonially nesting reptiles with TSD. We examined nest-site fidelity and nest-site choice in tuatara over 5 years on Stephens Island, New Zealand. Female tuatara nested every 2-4 years and showed high fidelity to nesting rookeries. Over 93% of females nested in the same rookery at least twice in 5 years. Approximately 25% of nests contained conspecific cues from previous nesting seasons, indicating that some females choose nest sites based on locations already selected by conspecifics. In experimental plots, female tuatara selected nest sites with loose soil and minimal vegetation, but they showed no preference for shaded compared with unshaded sites. This study provides insight into the development of colonial nesting structures in reptiles in that females are both attracted to nesting areas used by conspecifics, and show strong site fidelity to areas they have used in the past.