T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Shearwater (Buller's) Ardenna bulleri

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Procellariiformes
Family: Procellariidae
Genus: Ardenna
Species: A. bulleri
Binomial name: Ardenna bulleri
Synonym: Puffinus bulleri
Common names:  Buller's Shearwater, Grey-backed shearwater, New Zealand shearwater.

Buller’s shearwaters are medium to large-sized, Pacific species of pelagic seabirds that only breed on the Poor Knights Islands off Tutukaka near Whangarei, northern New Zealand.
Buller’s shearwaters have an average length of 46 cm and a weight of about 420 gm and have a wingspan of 97–99 cm. The upperside of Buller's shearwater is bluish grey. There is a distinctive M-shaped banding pattern with light grey interspersing areas on its upperside while flying. 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, under bright light it may appear almost white. 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. The rectrices (tail feathers of a bird controlling direction during flight) are blackish and the tail is wedge-shaped. The black bill is long, slender with a sharp hook to seize prey. Their legs and feet are dark brown-mauve on the outside and pink on the inside.
Buller’s shearwaters are common around much of New Zealand, especially in the Hauraki Gulf and Bay of Plenty. They feed mainly on small fish and krill, and regularly associate with large shoals of fish near the surface. After breeding, they migrate to the North Pacific Ocean where they congregate along oceanic currents east of Japan. Buller’s shearwaters are also regular visitors to the North American coast in the boreal autumn.

Buller’s shearwater is a colonial nester. The breeding season on the Poor Knight islands starts in September and lasts for almost half a year. Breeding occurs in burrows 0.6-3.2 m long dug on well-drained slopes in dry spongy soils or in clay soils amongst rocks. The burrows end in a nest that is lightly lined. A single white egg (65 x 43 mm) is incubated for about 51 days, with the parents changing between incubation and feeding every four days or so. The chicks fledge in May, when about 100 days old.

In the past, it was heavily used as a food source by the Māori, and on Aorangi Island it suffered massive predation by feral pigs. Its population had crashed to a low of just 100-200 pairs on Aorangi Island in the late 1930s. The pigs were removed from the island in 1936, and the shearwater population recovered, numbering 200,000 pairs again in the early 1980s to approach carrying capacity on the island at the end of the 20th century. At all times however, the colonies at Tawhiti Rahi Island and on the smaller islets could supply birds for the resettlement of Aorangi, and Buller's shearwater was never considered threatened with extinction in the foreseeable future. Indeed, it is a very abundant bird, with an estimated world population of 2.5 million birds. New introductions of mammalian predators are a potential risk, as are fires on these dry northern islands. At sea, oil spills are a major threat with the colony lying close to the shipping lane for the main oil terminal in New Zealand. The Rena oil spill resulted in the deaths of at least 156 Buller’s shearwaters that became coated in oil. Some Buller’s shearwaters are caught as by-catch during fishing operations.
This species is classified as vulnerable by the IUCN: a single localized catastrophe could wipe the species out.


  


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