Nest-site microhabitat influences hatching success, hatchling phenotype, and offspring sex in reptile species with temperature-dependent sex determination. 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 parental reproductive success. Moreover, some females copy the nest-site choices of conspecifics rather than assessing potential nest-sites themselves and making independent choices. Tuatara (Sphenodon punctatus), sole members of the ancient order Sphenodontia, are colonially-nesting reptiles with temperature-dependent sex determination. We studied nesting ecology of tuatara over five years on Stephens Island, New Zealand to address nest-site fidelity and nest-site choice.

Results/Conclusions Female tuatara nested, on average, every 2.5 years in this population. They showed extremely high fidelity to nesting rookeries, with over 93% of females nesting in the same rookery over multiple years. Female tuatara selected nest-sites with loose soil rather than hard soil, and bare areas rather than vegetated areas, but they showed no preference for shaded compared to unshaded sites. Approximately 25% of nests contained conspecific cues from earlier nests such as eggs, eggshells, or emerging hatchlings, indicating that some females choose nest locations based on sites previously selected by conspecifics. This study shows that although female tuatara are attracted to nest-sites with particular microhabitat characteristics, they may also copy the nest-site choices of previous females. Since females are attracted to nesting areas used by conspecifics, and show strong site fidelity to nesting areas they have used in the past, our study provides insight into the development of a colonial nesting structure in reptiles.