Is cool egg incubation temperature a limiting factor for the translocation of tuatara to southern New Zealand?

Conservation strategy for maintaining and protecting tuatara (Sphenodon punctatus), a rare endemic reptile from New Zealand, includes the reinstatement of populations through the past historical range. A proposal exists to translocate tuatara from Stephens Island in Cook Strait to the Orokonui Ecosanctuary (Te Korowai o Mihiwaka), a coastal site in southern New Zealand. The proposed site is within the former latitudinal range of the genus, but lies outside the current distribution of tuatara, where the climate is warmer. In this study, we examined whether cool incubation temperature is a limiting factor for the proposed reintroduction of tuatara to Orokonui. The tuatara is a species with temperature-dependent sex determination, with only females being produced at low incubation temperatures. Thus, cool southern temperatures may produce only females, even if incubation temperatures are high enough to support successful development. We experimentally translocated tuatara eggs to the ecosanctuary and found that nest temperatures were consistently below those of nests in their current natural distribution and would produce only female hatchlings if successful incubation occurred. An addition of sand to soil did not raise temperatures sufficiently to produce both sexes. However, additional assessments of soil temperatures in a third year indicated that some new sites were warm enough for males to be produced. Given that other aspects of site suitability appear favourable, and that global temperatures are predicted to rise in the near future, which should produce a more viable incubation environment, translocation of this long-lived reptile to the southern ecosanctuary is worth further exploration. However, monitoring of female nesting behaviour, including nest locations, depths and resulting temperatures, will be essential. Our study demonstrates an experimental approach for assessing site suitability for translocation that may be relevant to other egg-laying reptiles.