The influence of the tuatara on fairly prion breeding on Stephens Island, Cook Strait

Fairy prions, Pachyptila turtur, breed in large numbers on Stephens Island in north-western Cook Strait. The 1974-75 breeding cycle was followed with the aid of observation burrows. Laying, hatching and chick departure times were between those previously observed by Harper (1976) on the Poor Knights Islands and Richdale (1945, 1965) in Foveaux Strait. Tuatara, Sphenodon punctatus, are also numerous on the island and often share burrows with the prions. They were directly responsible for the loss of more than one quarter of the eggs and chicks, by predation and interference in the nesting chamber. This mortality is not considered to be a major factor in the regulation of fairy prion populations. That the tuatara-petrel relationship is complex, frequently aggressive, and almost exclusively favours the reptile, is emphasised by this study.