Nesting ecology and behaviour of tuatara (Sphenodon punctatus) at Ōrokonui Ecosanctuary

Abstract

Understanding the ecology of reproductive behaviours is an essential aspect in studying an animal species. Tuatara (Sphenodon punctatus), once widespread across New Zealand, have become severely restricted in distribution since the arrival of humans, due to the pressures of habitat destruction and introduced predators. Efforts to conserve and restore populations have included the translocation of individuals from islands to mainland ecosanctuaries. One transfer in 2012 occurred between Stephens Island (Takapourewa) in Cook Strait and Ōrokonui Ecosanctuary, 630 km to the south, near Dunedin. This translocation involved 30 wild adults, as well as 57 juveniles from wild and captive sources. Dunedin is several degrees colder than Stephens Island, so it is expected that this translocation may have some effect on the seasonal and reproductive behaviours of the ectothermic tuatara, an endemic reptile with temperature-dependent sex determination.

This research aims to determine the current seasonal timing of reproductive behaviours and patterns of nocturnal activity at Ōrokonui, to describe observations of natural nests constructed at Ōrokonui, and to use temperature data loggers to compare nest sites and to make predictions on hatching time and sex ratios of clutches. As Ōrokonui is, on average, colder than Stephens Island, I predicted that reproductive behaviours would occur later in summer relative to Stephens and that clutches would have long incubation times and a female-skewed sex ratio. Monitoring was carried out from November 2017 to April 2018 and over a second nesting season from October to December 2018 using trail cameras and visual searches during the day and night.

I determined that tuatara at Ōrokonui have two main periods of high activity levels during the summer, in November and then between February – April. Nesting behaviours primarily occurred between mid-November and mid-December. Nesting behaviours occurred in two location types, under the fenceline and in a gravel pile. I located and excavated two nests during the 2017-2018 active season. Temperature records obtained from one of the nests recorded thermal conditions experienced by the clutch, enabling prediction of the time of hatching and sex ratio. I predict a nest of females as well as a long incubation time of close to two years, due to the low temperatures experienced. The findings from this research will provide information on the effect of translocation on the nesting ecology of tuatara, which can be used to help plan and manage future translocations and to predict the potential implications of climate change.