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Wedge-tailed Shearwater


The Wedge-tailed Shearwater, Puffinus pacificus is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a Muttonbird, like the Sooty Shearwater of New Zealand and the Short-tailed Shearwater of Australia. It ranges across from throughout the tropical Pacific and Indian Ocean roughly between latitudes 35N and 35S. It breeds in islands such as off Japan, the Islas Revillagigedo, the Hawaiian Islands, the Seychelles and off Western Australia.

Description

The Wedge-tailed Shearwater is the largest of the tropical shearwaters. There are two colour morphs of the species, dark and pale; the pale morphs predominate in the North Pacific, the dark morph elsewhere. However, both morphs exist in all populations, and bear no relation to sex or breeding condition. The pale morph has grey-brown plumage on the back, head and upperwing, and whiter plumage below. The darker morph has the same dark grey-brown plumage over the whole body. The species common name is derived from the large wedge-shaped tail, which may help the species glide. The bill is dark and legs are flesh coloured, with the legs set far back on the body (in common with the other shearwaters) as an adaptation for swimming.

This species is related to the pan-Pacific Buller's Shearwater, which differs much in color pattern, but also has a wedgetail and a thin black bill . They make up the Thyellodroma group, a superspecies in the large shearwaters of the proposed genus Ardenna .

Diet

Wedge-tailed Shearwaters feed pelagically on fish, squid and crustaceans. 66% of their diet is fish, of which the most commonly taken is goatfish. It was thought that the species mostly took food from surface feeding, observations of feeding Wedge-tails suggested that contact-dipping, where birds flying close to the surface snatch prey from the water was the most commonly used hunting technique. However, a 2001 study which deployed maximum depth recorders found that 83% of Wedge-tails dived during foraging trips with a mean maximum depth of 14 m and that they could achieve a depth of 66 m .

Breeding behaviour

The Wedge-tailed Shearwater breeds in colonies on small tropical islands. Breeding seasons vary depending on location, with synchronised breeding seasons more common at higher latitudes. Northern hemisphere birds begin breeding around February, southern hemisphere birds begin around September. Wedge-tailed Shearwaters display natal philopatry, returning to their natal colony to begin breeding at the age of four.

Wedge-tailed Shearwaters are monogamous, forming a long term pair bond that lasts for several years. Divorce between pairs occurs after breeding seasons that end in failure. Nesting either in burrows or sometimes on the surface under cover. Pairs call frequently as a pair, both to reinforce the pair bond and warn intruders away from their territory. Parents also call to their chicks. The call is long, with an inhaling component (OOO) and exhaling component (err); their Hawaiian name uau kani means moaning petrel. Both sexes participate in digging a burrow, or repairing the burrow from last year. Nesting burrows of other species are also used. The breeding season of the Bonin Petrel in Hawaii is timed to avoid that of the Wedge-tail; in years where Bonin Petrel chicks are still in burrows when Wedge-tails return to begin breeding these chicks are killed or evicted. It attends these colonies nocturnally, although non-breeding Wedge-tails are often seen at the surface throughout the day and breeding birds will rest outside their burrows before laying.

Both sexes undertake a prelaying exodus in order to build up energy reserves, this usually lasts around 28 days. A single egg is laid, if that egg is lost then the pair will not attempt another that season. After laying the male usually undertakes the first incubation stint. Both sexes incubate the egg, in stints that can last up to 13 days. Incubation takes around 50 days. After hatching the chick is brooded for up to six days, until it is able to thermoregulate, after which it is left alone in the nest while both parents hunt for food. It is initially fed with stomach oil, an energy rich waxy oil of digested prey created in the parents gut; later it is fed both solids and stomach oil. Unlike many procellariids Wedge-tailed Shearwater parents to not alternate long and short trips to provide food, but return regularly. Chicks increase in size to 560 g (larger than the adults) then drop to around 430 g before fledging. Fledging occurs after 103-115 days, after which the chick is independent of the adult.

Known breeding colonies include:

Heron Island, Australia

Lady Elliot Island, Australia

Lord Howe Island, Australia

Montague Island, Southern New South Wales, Australia

North West Island, Australia

Muttonbird Island, Coffs Harbour, Northern New South Wales, Australia

Manana Island, Hawaii, USA

Media


References

Austin, Jeremy J. (1996): Molecular Phylogenetics of Puffinus Shearwaters: Preliminary Evidence from Mitochondrial Cytochrome b Gene Sequences. Molecular Phylogenetics and Evolution 6(1): 7788. (HTML abstract)

Austin, Jeremy J.; Bretagnolle, Vincent & Pasquet, Eric (2004): A global molecular phylogeny of the small Puffinus shearwaters and implications for systematics of the Little-Audubon's Shearwater complex. Auk 121(3): 847864. DOI: 10.1642/0004-8038(2004)121[0847:AGMPOT]2.0.CO;2 HTML abstract

Database entry includes justification for why this species is of least concern

Burger, A. (2001): Diving depths of Shearwaters Auk 118(3):755759 DOI: 10.1642/0004-8038(2001)118[0755:DDOS]2.0.CO;2 HTML abstract HTML fulltext (without images)

Penhallurick, John & Wink, Michael (2004): Analysis of the taxonomy and nomenclature of the Procellariformes based on complete nucleotide sequences of the mitochondrial cytochrome b gene. Emu 104(2): 125-147. (HTML abstract)

External links

BirdLife Species Factsheet

IUCN Red List

California Bird Records Committee: Rare Bird Photos - Wedge-tailed Shearwater

USFWS, Midway Atoll NWR: Wedge-tailed Shearwater

Frank O'Connor's Birding Western Australia: Some more photos of the Wedge-tailed Shearwater

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Wedge-tailed Shearwater


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