Buller's Shearwater

Overview

Buller's shearwater (Ardenna bulleri), also known as the grey-backed or New Zealand shearwater, is a Pacific seabird in the family Procellariidae. It is one of the larger shearwaters and forms a superspecies with the wedge-tailed shearwater. Despite an estimated world population of 2.5 million birds, it is classified as Vulnerable due to its restricted breeding range.

Identification

• Length of 46–47 cm with a 97–99 cm wingspan and a weight between 342–425 g.
• Bluish grey upperside featuring a distinctive broken black 'M' pattern across the wings, created by blackish primaries and a stripe from the tertials that do not meet at the hand.
• Bright white underside with grey extending down to eye level on the head, creating conspicuous white cheeks.
• Blackish tail and rectrices, with a dark bill and irises.

Habitat

This pelagic species is a transequatorial migrant that ranges across most of the Pacific Ocean outside the breeding season, though it is notably absent from the subantarctic Pacific and much of Melanesia. It breeds colonially in burrows, rock crevices, or under tree roots on the Poor Knights Islands off northern New Zealand, preferring densely forested slopes but also using treeless cliffs.

Diet

Buller's shearwater feeds primarily on fish, squid, and crustaceans such as the krill Nyctiphanes australis. It catches food at a head's length below the surface by picking it up with the bill or briefly inserting its head while swimming, occasionally joining mixed-species feeding flocks or following fishing trawlers.

Did you know?

Although the species numbers approximately 2.5 million individuals, it is classified as Vulnerable because it breeds on only a few islands, making it susceptible to extinction from a single localized catastrophe. Feral pigs on Aorangi once drove the population down to just 100–200 pairs, from which it recovered only after the pigs were removed in 1936.