The breeding biology of Hutton's Shearwater

Abstract

Hutton's Shearwater, Puffinus huttoni, is a small endangered seabird that breeds at only two sites in the Seaward Kaikoura Mountains, New Zealand. The alpine habitat has restricted access and research on the species' breeding ecology. The extreme breeding habitat may also impose reproductive costs on Hutton's Shearwaters because of the energy needed to fly to colonies. Within the Kowhai Valley colony burrows were located on moderate to steep-angled slopes wherever the soil was deep and friable enough to burrow. Available breeding habitat may be a factor limiting the population. Breeding burrows were generally simple and non-branched. Males were larger than females in all measured body dimensions (bill length, bill depth, bill width, head length, head width and tarsus length), with the exception of wing length. Egg-laying within the colony was non-synchronous and took up to 38 days. The peak of egg laying occurred around 8 and 9 November in the 1998/99 and 1997/98 seasons respectively. The incubation period lasted for an average of 50.3 days and chicks fledged at an average age of 83.8 days. This fledging period is longer than that reported for the closely related Manx Shearwater, Puffinus puffinus. There were seasonal differences in the rate of mass gain by Hutton's Shearwater chicks. Mass gain by Hutton's Shearwaters was lower than that found in Manx Shearwaters and this may explain the extended fledging period. However, generally the results indicate that, despite the high altitude and extreme location of the breeding colonies, the breeding biology of Hutton's Shearwater fits the pattern observed in other species of Puffinus.