Buller's shearwater
A Pacific seabird with a distinctive M-shaped wing pattern.
Wikipedia / Wikimedia Commons
Buller's shearwater, also called the grey-backed or New Zealand shearwater, is a Pacific seabird from the family Procellariidae. It belongs to the black-billed wedge-tailed Thyellodroma group, which includes the larger members of the genus Ardenna, and it shares a superspecies relationship with the wedge-tailed shearwater.
Adults measure 46–47 cm long with a wingspan of 97–99 cm and weigh between 342 and 425 g. Their upperparts are bluish grey, marked by a blackish stripe running from the tertiary remiges to the primary wing coverts. The primary remiges are also blackish, but these two dark areas do not meet at the hand; instead, a light grey patch sits between them, appearing almost white in bright light. When the bird is seen from above, this pattern forms a broken black "M" with light grey gaps. The underside is bright white, and on the head, the grey extends down to eye level, making the white cheeks stand out—similar to the smaller Puffinus shearwaters. The tail is wedge-shaped and blackish, the bill and irises are dark, and fledged juveniles already show adult coloration, while nestlings are covered in grey down. At sea, this species is unusually easy to pick out: its large size and the distinctive M-shaped band on the upper side, unique among its genus, make it look more like a gadfly petrel, prion, or blue petrel—though those birds are much smaller, roughly two-thirds the length and wingspan and less than half the bulk.
Like other Ardenna shearwaters, Buller's shearwater is pelagic and a transequatorial migrant, ranging across most of the Pacific outside breeding season. It appears in subarctic waters off Kamchatka and the Aleutian Islands but has not been recorded in the subantarctic Pacific, possibly because that vast, islandless region south of the Polynesian Triangle is poorly studied. Off the west coast of the United States, it is fairly common in late summer and early autumn and can often be seen close to land along temperate and tropical American coastlines. Its near absence from most of Melanesia and western Micronesia—areas with plenty of human activity and sea traffic—is likely genuine; only isolated records exist from the Marianas, Palau, and Yap, west and southwest of the Marshall Islands. One vagrant was even recorded in the Atlantic, off New Jersey. The diet consists mainly of fish, squid, and crustaceans like the krill Nyctiphanes au
- Scientific name
- Ardenna bulleri
- Length
- 46–47 cm (18–19 in)
- Wingspan
- 97–99 cm (38–39 in)
- Weight
- 342–425 g (12.1–15.0 oz)
- IUCN status
- Vulnerable
- Estimated world population
- 2.5 million birds
Lore & Background
Buller's shearwater is a pelagic, transequatorial migrant ranging across most of the Pacific Ocean outside the breeding season. It occurs in subarctic waters off Kamchatka and the Aleutian Islands, but is not documented in the subantarctic Pacific, possibly due to lack of study opportunities. It is fairly common off the west coast of the United States during late summer and early autumn, and can be observed along temperate and tropical coastlines of the Americas. Its absence from most of Melanesia and western Micronesia is probably genuine, with only isolated records from the Marianas, Palau, and Yap. A vagrant was recorded once in the Atlantic, offshore New Jersey, United States.
The species feeds mainly on fish, squid, and crustaceans such as the krill Nyctiphanes australis. It occasionally follows ships and may join mixed-species feeding flocks. Food is caught at most a head's length below the surface, either picked up with the bill in flight or by briefly inserting the entire head while swimming. It rarely dives out of flight or plunges from the water's surface.
It is a colonial nester, breeding predominantly on Tawhiti Rahi and Aorangi, the main islands of the Poor Knights group offshore northern New Zealand. Nests are in burrows, rock crevices, or under tree roots, preferring densely forested slopes, though it also breeds on treeless stacks or cliffs. A pair was observed breeding on the Simmonds Islands in 1980, but this seems isolated. The breeding season starts in October and lasts almost half a year. A single egg is incubated for about 51 days, with parents changing every 4 days. Time to fledging is not well known but assumed to be around 100 days by analogy with relatives.
Reader's Guide
Buller's shearwater is significant as a very abundant seabird with an estimated world population of 2.5 million birds, yet it is classified as vulnerable by the IUCN because it is not known to occur on any larger island outside the Poor Knights Islands, meaning a single localized catastrophe could wipe the species out. Historically, it was heavily used as a food source by the Māori, and on Aorangi it suffered massive predation by feral pigs, with its population crashing to just 100–200 pairs in the late 1930s. After pigs were removed in 1936, the population recovered to 200,000 pairs in the early 1980s, approaching carrying capacity by the end of the 20th century. The species was never considered threatened with extinction in the foreseeable future, as colonies on Tawhiti Rahi and smaller islets could supply birds for resettlement of Aorangi. Its distinctive M-shaped banding pattern on the upperside makes it unusually easy to identify at sea, unique among its genus and more akin to some gadfly petrels, prions, and the blue petrel, though those are much smaller birds.
Did You Know?
- Buller's shearwater is also known as the grey-backed shearwater or New Zealand shearwater.
- Its upperside shows a broken black 'M' pattern with light grey interspersing areas, unique among its genus.
- The species was never considered threatened with extinction, even after its population on Aorangi crashed to 100–200 pairs in the late 1930s.
- A vagrant Buller's shearwater was recorded once in the Atlantic, offshore New Jersey, United States.
Frequently Asked Questions
What is Buller's shearwater?
Buller's shearwater (Ardenna bulleri) is a Pacific seabird in the family Procellariidae, also going by the names grey-backed shearwater and New Zealand shearwater. It sits within the black-billed wedge-tailed Thyellodroma group, which lumps together the larger members of the genus Ardenna.
How big is Buller's shearwater?
Adults measure 46 to 47 cm in body length with a wingspan of 97 to 99 cm, and they tip the scale at roughly 342 to 425 grams. That size places them among the bigger Ardenna species in their group.
What is the M-shaped wing pattern on Buller's shearwater?
A blackish stripe runs from the tertiary feathers up to the primary wing coverts, and the primary remiges are dark as well, together forming a striking M-shaped mark when the bird spreads its wings. This pattern is one of the quickest visual cues for telling it apart from the similar wedge-tailed shearwater.
How is Buller's shearwater related to the wedge-tailed shearwater?
The two are part of the same superspecies complex, meaning they were long treated as a single species before being formally split into separate taxa. Both belong to the black-billed wedge-tailed Thyellodroma group of Ardenna, sharing close evolutionary ties and overlapping morphology.
What is the conservation status of Buller's shearwater?
The IUCN currently classifies Buller's shearwater as Vulnerable, with an estimated global population of around 2.5 million birds. Despite that relatively large number, ongoing pressures have kept the species in a threatened category rather than a secure one.
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