Tuatara, temperature and translocation

Professor Alison Cree is a reproductive biologist, working in the Department of Zoology at the University of Otago. A key focus of her research is the effect of temperature on New Zealand’s native reptiles.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Alison Cree

Professor Alison Cree spends a lot of time out in the field collecting data. In this photo, she is downloading information about soil temperature from a data logger.

Alison led a project investigating the viability of translocating tuatara to Orokonui Ecosanctuary. The research work carried out by Anne Besson, one of Alison’s PhD students, was an important part of this project.

Tuatara distribution

Tuatara were once widespread in New Zealand. Fossil evidence suggests that this unique, endemic reptile previously lived as far south as Bluff. Since human arrival and the introduction of mammalian predators, tuatara have become restricted to a few dozen offshore islands in Cook Strait and northern New Zealand.

Orokonui Ecosanctuary is a ‘mainland island’ situated close to Dunedin. Mammalian predators have been eradicated, and a predator-proof fence surrounds the sanctuary. A proposal to translocate tuatara from an island in Cook Strait required further research to see if the cooler temperatures in Otago would affect the success of the translocation.

Temperature effect on sex determination in tuatara

Sex determination is the process by which a new embryo becomes a male or a female. In many animals, the sex of the young is determined by a specific chromosome in the father’s sperm. For some reptiles, including tuatara, things work a little differently!

Tuatara have a system called temperature-dependent sex determination. In this system, the sex of the new organism is still undecided when the egg and sperm meet. Tuatara lay their eggs in soil, and the temperature of the surrounding soil determines the sex of the offspring – warmer temperatures produce males and cooler temperatures produce females.

Translocation and soil temperature

Anne Besson’s PhD research investigated how tuatara might respond to the cooler temperatures in Otago. The most important research question that Anne and Alison hoped to answer was whether the soil temperatures at Orokonui Ecosanctuary would be warm enough for the eggs. In particular, they wanted to know whether the soil temperatures would be warm enough to produce both males and females at the end of the egg incubation process.

Anne used special data loggers that she buried in the soil. These miniature pieces of equipment, about the size of a 50 cent coin, can record the soil temperature over long periods and store the information. This information can then be transferred to a laptop and analysed. Anne used data loggers at a number of sites in Otago to see how the soil temperatures compared with temperatures that tuatara eggs experience in their natural habitat on Stephens Island in Cook Strait.

Disappointingly, Anne’s initial results did not find any sites warm enough to ensure that some males would hatch. However, the following year, the research team recorded warmer temperatures at some sites. This raises optimism that both sexes can be produced at the sites, but longer-term monitoring is required.

Tuatara on the move

In March 2009, 15 juvenile tuatara were moved to Orokonui Ecosanctuary. The tuatara were placed into a secure, outdoor rearing enclosure so they could be closely monitored. There were additional translocations in 2012 and 2016–17. Tuatara have spread through new parts of Orokonui and in 2020, hatchilings were sighted. Ecosanctuary staff and university researchers work in consultation with the Department of Conservation and iwi, including Ngāti Koata and Ngāi Tahu, regarding the conservation of tuatara at Orokonui.