SummaryThe breeding cycle and habits of the White-headed Petrel,Pterodroma lessoni, have been observed over parts of two nesting seasons at Macquarie Island. These birds are strictly nocturnal on land and are the commonest burrowing species on the island. Their numbers appear to be declining and factors responsible for this include predation by feral cats, competition with rabbits for burrows, and loss of soil cover through rabbit-induced erosion.The While-headed Petrels arrive at the island from the third week of August after an absence of about 11 weeks. There is a long re-occupation period. The same individuals may breed in the same nest during successive seasons. Egg-laying occurs between November 24 and December 16. incubation being undertaken by both sexes in turn and extending over eight to nine weeks.The chicks are unguarded when two to three days old and are fed rather irregularly by both parents. One chick flew when it was about 102 days old. The chicks threaten intruders by lunging and by spitting stomach oil but this ability declines with increasing age.Adults undergo a body moult while breeding, but wing moult is delayed until nesting is over.