Buller's Shearwater

Adults birds are 46–47 cm (18–19 in) in length, with a 97–99 cm (38–39 in) wingspan, and have been recorded to weigh 342–425 g (12.1–15.0 oz). The upperside of Buller's shearwater is bluish grey. A blackish stripe runs from the tertiary remiges to the primary wing coverts. The primary remiges are blackish, also; the two black areas do not meet at the hand, however; the area between them is a rather light grey, and under bright light may appear almost white. With the bird facing upwards, the pattern gives the impression of a broken black "M", with light grey interspersing areas. The underside is bright white; on the head the upperside's grey extends town to eye height and the white cheeks may shine up conspicuously, as in the smaller shearwaters of Puffinus sensu stricto. The rectrices are blackish and the tail is wedge-shaped; the bill and irises are dark. Fledged juveniles already have the adult's colouration; the nestlings are covered in grey down feathers. Compared to other shearwaters, the species is unusually easy to identify at sea by its combination of considerable size and the distinctive, M-shaped banding pattern on its upperside while flying, uniquely among its genus and more akin to some gadfly petrels (Pterodroma), the prions (Pachyptila) and their relative, the blue petrel (Halobaena caerulea). …

This species is pelagic like the other Ardenna shearwaters; it is a transequatorial migrant ranging across most of the Pacific Ocean outside the breeding season. Though it occurs in the subarctic waters off Kamchatka and the Aleutian Islands, it is not documented in the subantarctic Pacific; this apparent absence might simply be due to the lack of study opportunities in the vast islandless region south of the Polynesian Triangle, however. It is fairly common well off the west coast of the United States during late summer and early autumn, and can generally be observed not far from land along the whole temperate and tropical coastlines of the Americas. Its general absence from most of Melanesia and western Micronesia – where human settlement and sea traffic are considerable – is thus probably genuine; only isolated records, such as from the Marianas, Palau, and Yap, exist from west and southwest of the Marshall Islands. A vagrant bird was also recorded in the Atlantic once, offshore New Jersey, United States. Buller's shearwater feeds mainly on fish, squid, and crustaceans such as the krill Nyctiphanes australis. It does occasionally follow ships, such as fishing trawlers, and may be part of a mixed-species feeding flock. …