From 1963 to 1981 data were collected on the breeding of the Buller’s Shearwater (Puffinus bulleri) . The world population, roughly 2.5 million birds, occupies 7 of the 12 islands, islets, and stacks of the Poor Knights Islands (35″30’S; 174″44’E). Buller’s Shearwaters return from their 4.5 month trans-equatorial migration on about 10 September. Numbers build up rapidly with breeding birds digging burrows averaging 1.01 + 0.2 m in length. Caverns, caves, and Maori stone walls also serve as nest sites. Nest refurbishing is complete by about 26 October, when copulation occurs. The prelaying exodus follows about 32 h later, with most birds absent from the isIands’ vicinity for about 30 days until 25 November. Eggs appear from 26 to 30 November. Females without nests lay eggs on the ground until 3 December; these eggs are eaten by tuataras and small lizards. Average dimensions of 74 eggs were 65.44 +/- 0.29 x 42.96 +/- 0.22 mm; and average weight of 27 fresh eggs 66.76 +/- 0.85 g. Surface eggs are narrower than burrow eggs. The incubation period is c. 51 days with both sexes sharing duties. Four nights is the average shift; females sit the first night and following day. Hatching occurs about 19 January; most fledglings leave the islands in early May. Most of the few adult P. bulleri that die on the breeding grounds are ensnared in tree saplings. Numbers on Aorangi have expanded rapidly from c. 100 pairs in 1938 to about 200,000 pairs in 1981. P. bulleri is an aggressive coloniser, displacing gadfly petrels and smaller shearwaters for nesting space. and may soon be colonising the Three Kings and other nearby islands.