Tuatara, male emerging from under log,
Poor Knights Islands
Tuatara once lived throughout the mainland of New Zealand but have survived in the wild only on 32 offshore islands.
These islands are characteristically free of rodents and other introduced mammalian predators which are known to prey on eggs and young as well as compete for invertebrate food. The islands are usually occupied by colonies of breeding seabirds that contribute to the fertility and hence the richness of invertebrate and lizard fauna needed by tuatara.
Recent advances in both the ability to eradicate rodents from islands and the captive incubation and raising of tuatara have allowed the species to be translocated to a further four islands they presumably inhabited in the past.
Until quite recently two species of tuatara were recognised and one of these was considered to comprise two subspecies.
The northern tuatara (Sphenodon punctatus punctatus) present on islands from the Bay of Plenty north, and the Cook Strait tuatara (S. punctatus) an unnamed subspecies present on Takapourewa (Stephens Island) and the Trio Islands in Marlborough Sounds.
The other species was the Brothers Island tuatara (S. guntheri) known naturally from one small island in Marlborough Sounds. In 2009 research examined DNA and allozyme data for all populations and concluded that tuatara is best described as a single species that contains distinctive and important geographic variants.