Buller's Shearwater

The Buller's shearwater, known scientifically as Ardenna bulleri, is a striking seabird of the Pacific, also referred to as the grey-backed shearwater or New Zealand shearwater. This species is a member of the black-billed wedge-tailed Thyellodroma group and is among the larger shearwaters within the genus Ardenna. It is closely related to the wedge-tailed shearwater, forming a superspecies with it.

Identification Tips

Adult Buller's shearwaters measure approximately 46–47 cm in length, with a wingspan of 97–99 cm, and weigh between 342–425 g. The upper parts are bluish-grey, with a distinctive blackish stripe running from the tertiary remiges to the primary wing coverts. The primary remiges themselves are blackish, but interestingly, the two black areas do not meet at the hand, leaving a light grey, almost white area in between. This creates an M-shaped pattern when the bird is in flight. The underside is a bright white, and the cheeks may shine conspicuously. The tail is wedge-shaped, and both the bill and irises are dark.

Habitat

Buller's shearwaters are pelagic birds, spending most of their life at sea. They are known to breed predominantly on the Poor Knights Islands off northern New Zealand.

Distribution

These birds are transequatorial migrants, traversing most of the Pacific Ocean outside the breeding season. They can be found from subarctic waters off Kamchatka and the Aleutian Islands to the temperate and tropical coastlines of the Americas. They are generally absent from most of Melanesia and western Micronesia.

Breeding

The breeding season commences in October and lasts nearly half a year. They lay a single egg, which is incubated for about 51 days. The time to fledging is assumed to be around 100 days, by analogy with related species.

Similar Species

Buller's shearwater is unique among its genus for its M-shaped banding pattern on its upperside while flying, which distinguishes it from similar species.

Diet and Feeding

Their diet consists mainly of fish, squid, and crustaceans such as krill. They typically feed at a head's length below the surface, either by picking up food with their bill or briefly inserting their entire head while swimming.

Conservation Status

The IUCN classifies Buller's shearwater as Vulnerable. While the species is abundant, with an estimated world population of 2.5 million birds, its restricted breeding range on the Poor Knights Islands means that a single localized catastrophe could have devastating effects.