THE GREATER SHEARWATER PUFFINUS GRAVIS AT‘ ITS BREEDING GROUNDS.

Abstract

Summary. An account is given of the breeding cycle of the Greater Shearwater, with speciat reference to the colony (estimated at 4,000,000 breeding birds) at Nightingale Island in the Tristan da Cunha group. The birds arrive at the breeding grounds during late August and September. There is a brief laying season during the second week of November and the chicks hatch early in January. In April the adults desert their young, when they are full–grown but still in down. Fully feathered juveniles are found at the beginning of May and start flying towards the end of the first week of May. As far as is known the juveniles have all left the breeding grounds by early June. Special points of interest relating to the breeding cycle are:.‐(a) The presence of Greater Sheanvaters at the breeding grounds in large numbers at least one–and–a–half months in advance of the laying season. (b) The overcrowding of the breeding grounds at Nightingale. (c) The courtship ceremonies. (d) A strongly developed diurnal habit during the breeding season, although the birds are most active after 4 p.m. (local time) and at night. (e) The presence of large numbers of juveniles at the breeding grounds during May. (f) The apparent absence of adults from their burrows. from mid–April onwards. The occurrence of the Greater Sheanvater at the north–easterly limits of its range at the time breeding IS beginning suggests that a proportion of the population fails to breed each year, and that the main return from the north takes place in mid–ocean, and down the west side of the Atlantic, mainly in August. Flight and locomotion are described. Data collected on the exploitation of this species by the Tristan islanders show that the annual depletions are not more than l% of the estimated Shearwater population at Nightingale.