Introduction

This medium-sized, ground-nesting shearwater nests colonially on islands in tropical and subtropical portions of the Pacific Ocean. In the Hawaiian Islands, it breeds on offshore islets of the main islands (Ka‘ula, Moku Manu, and Lehua) and in the Northwestern Hawaiian Islands from Nihoa to Kure Atoll, except Necker Island and Gardner Pinnacles. Separate populations breed on Johnston Atoll, Ducie and Oeno Islands (Pitcairn Islands), Sala y Gomez (Chile), MotuNui (Easter Island), and in the Marquesas, Tuamotu, Line, Phoenix, and Austral groups. With the exception of populations in the Hawaiian and Line Islands, little is known about breeding populations in the remainder of the species’ range. This species has been extirpated from Ogasawara Islands, Minami Torishima, and Wake Island in the western Pacific.

The total breeding population in the Hawaiian Islands is estimated at approximately 2,500–3,300 pairs. The largest breeding colony in the archipelago, 1,500–2,000 nesting pairs, is found on Laysan Island. Although small by seabird standards, other large populations can be found on Christmas Island (Kiritimati, 6,000 nesting pairs), Pitcairn Islands (3,000 pairs), and Sala y Gomez (400–2,500 pairs).

The Christmas Shearwater is a member of a highly aquatic group of shearwaters. It feeds on fish and squid by seizing them at or near the surface, dipping, and pursuit-plunging, although Christmas Shearwaters do not dive far below the water surface. Among its most important prey in the Northwestern Hawaiian Islands and Christmas Island are squid, goatfishes, and flying fishes. Foraging occurs over schools of predatory fish (tuna) that force prey to the surface.

Breeding colonies are widely spaced, small, and remote. Individuals are active at dawn and at night on the breeding grounds. It is this characteristic, as well as pelagic feeding and nocturnal habits, that makes the Christmas Shearwater one of the less studied seabirds in the Pacific Ocean. Minor studies, conducted in the Northwestern Hawaiian Islands (Howell and Bartholomew 1961; Udvardy 1963; Harrison et al. 1983; Fefer et al. 1984; Pettit et al. 1984, 1985; Niethammer et al. 1992; NWHS) and Christmas Island (Ashmole and Ashmole 1967, 1968), have focused on food habits, metabolism, temperature regulation, general breeding biology, and reproductive success. Information on this shearwater’s marine and nonbreeding range is lacking, and the current status of populations in the Pacific remains unknown. Many colonies have declined and continue to be threatened by introduced mammalian predators, including humans, and by degraded habitat.