The wedge-tailed shearwater is the largest tropical shearwater, and occurs in two plumage forms: dark-bellied and pale-bellied. They are widely distributed throughout the tropical Pacific and Indian oceans, where they breed on tropical or subtropical islands, including the Kermadec Islands. Wedge-tailed shearwaters rarely reach waters off the New Zealand mainland, with most seen at sea off the north-east coast, and a few beach-wrecked on North Island coasts. Pale-bellied birds are rare in the South Pacific and western Indian Oceans, but comprise 20-30% of the Western Australian population, and almost 100% of the Hawaiian population.

Identification

The wedge-tailed shearwater population in the south-west Pacific is comprised of all-dark birds. They have a small head, slender body, and long tail. Their plumage is blackish-brown, with the feathers of the back and wings edged in slightly lighter brown. The chin, throat and forehead are brownish-grey, with the underparts dusky brown. Pale-bellied birds (mainly North Pacific) have a dark greyish-brown head, nape and upperparts, grading into the white chin and throat. Their underparts are mainly white with variable grey-brown mottling on the sides of the breast, flanks and undertail. The underwings are white with a broad dark trailing edge. The slender bill is dark slate grey, and the legs are pale flesh-coloured. The sexes are alike with no seasonal variation. In flight, wedge-tailed shearwaters alternate fast wing-beats with long glides.

Voice: on breeding grounds, wedge-tailed shearwaters make a wailing moan 'ka-whooo-ahh'. Colonies produce a cacophony of calls.

Similar species: the more southern-ranging flesh-footed shearwater is larger, bulkier and shorter-tailed, with a pale pink dark-tipped bill. Short-tailed shearwater is shorter (42 cm) but heavier (550 g), with a shorter bill, shorter tail, and greyish feet. Christmas Island shearwater is smaller and shorter-tailed, with dark legs and feet.

Distribution and habitat

The wedge-tailed shearwater is a widely distributed migratory species throughout the Pacific and Indian oceans. It breeds on many islands including Kermadec (New Zealand), Norfolk, Lord Howe, Fiji, Tonga, Samoa, Pitcairn, New Caledonia, Vanuatu, Solomon, Johnston Atoll, Christmas (Kiribati), Marshall, Caroline, Bonin, the Hawaiian archipelago, Madagascar, the Seychelles, and Reunion and islands off the west and east coasts of Australia and the west coast of Mexico.

Wedge-tailed shearwaters are pelagic in the tropical and subtropical Pacific and Indian oceans, mainly between 35°N and 35°S. Southern hemisphere birds migrate north of the Equator, with the Kermadec population migrating to the south-east North Pacific during the austral winter. Wedge-tailed shearwaters rarely reach waters off the New Zealand mainland, with a few recorded at sea between Cape Reinga and East Cape, or beach-wrecked birds on North Island coasts.

Population

The wedge-tailed shearwater has an estimated global population of 5 million+ birds, including an estimated 50,000+ pairs that breed at the Kermadec Islands (Raoul, Meyer and Herald Islets, Macauley, Curtis, Cheeseman and L'Esperance Rock).

Threats and conservation

Although it has a large estimated global population, the wedge-tailed shearwater may be declining in some areas due to changes in its food supply possibly linked to declining tuna stocks and changes in sea temperature. In 2002, unusually high sea-surface temperatures in the Great Barrier Reef were accompanied by reduced provisioning, decreased growth rates and reproductive failure of wedge-tailed shearwaters in the region. Over-exploitation through poaching or persecution is also likely to reduce some populations. Wedge-tailed shearwaters are vulnerable to predation by invasive species, including feral cats, rats and pigs, which kill and eat birds and eggs.

The bulk of the Kermadec Islands population breeds on Macauley Island where introduced Pacific rats were eradicated in 2006, and also on smaller islands (e.g. Curtis Island and the Herald Islets) that never had introduced predators. In contrast, the breeding population on Raoul Island (by far the largest island in the group) is a fraction of the immense numbers present there 100 years ago. The almost complete extirpation of wedge-tailed shearwaters on Raoul Island was due to predation by introduced cats and rats. Wedge-tailed shearwaters were rare on Raoul Island by 1966-1967, and no evidence for their presence was found in 1993-1994 (though a single bird was found in a burrow there in April 1998). Feral goats were eradicated from Raoul Island in 1984, followed by feral cats and rats in 2002. In 2008, 13 active wedge-tailed shearwater burrows were found on Raoul Island, signalling the start of a return to their former stronghold.

The IUCN Red List classifies wedge-tailed shearwater as Least Concern. The Department of Conservation classifies it as Relict (B; range restricted, and secure overseas), meaning that it remains numerous but now occupies less than 10% of its original range, reflecting the human-induced extirpation of the formerly enormous Raoul Island population.

Breeding

Wedge-tailed shearwaters breed from October to May at the Kermadec Islands, and are absent June-September. Breeding birds arrive from October with mating taking place during October-November. They are monogamous, and lay their single large (67 x 43 mm) white egg in December. Nests are usually in a burrow up to 2.5 m long, but may be on the ground under an overhanging rock, in a small cave, or under vegetation. Incubation takes 50-54 days and is shared by both adults. Eggs hatch in early February. The chicks grow much larger than adults during the nestling period, increasing to c.560 g before slimming down to c.430 g at fledging. Adults typically depart on migration 1-2 weeks before the chicks fledge around mid-May, at about 90 days-old. Wedge-tailed shearwaters start breeding at about 4 years-old.

Behaviour and ecology

The wedge-tailed shearwater is an annual breeder in dense colonies. They are usually solitary at sea, but sometimes form small feeding flocks or rafts at sea off colonies. Both adults dig the burrow using their bill and feet. After mating, both birds return to sea to feed for several weeks before egg-laying and incubation.

Food

Wedge-tailed shearwaters feed mainly on fish, including flying fish, plus squid, insects, jellyfish and prawns. They often form feeding flocks over tuna or dolphins, which drive smaller fish to the surface, where wedge-tailed shearwaters may form feeding aggregations with sooty and white terns, noddies and boobies. They are also attracted to fishing vessels. Wedge-tailed shearwaters forage by contact-dipping, surface-seizing and sometimes deep plunging, exceptionally diving up to 66 m below the surface (less than 14 m is typical).

Weblinks

BirdLife factsheet

Wikipedia

References

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Iredale, T. 1910. Birdlife on the Kermadec Islands. Emu 10: 2-16.

Marchant, S.; Higgins, P.J. (eds). 1991. Handbook of Australian, New Zealand & Antarctic birds. Vol. 1, ratites to ducks. Oxford University Press, Melbourne.

Medway, D.G. 2000. Rare Birds Committee – combined report for 1992–1999. Notornis 47: 64-70.

Merton, D. 1970. Kermadec Islands expedition reports: a general account of birdlife. Notornis 17: 147-199.

Robertson, C.J.R. (ed.) 1985. The complete book of New Zealand birds. Reader's Digest. Australia.

Robertson, H.A; Baird, K.; Elliott, G.P.; Hitchmough, R.A.; McArthur, N.J.; Makan, T.; Miskelly, C.M.; O’Donnell, C.F.J.; Sagar, P.M.; Scofield, R.P.; Taylor, G.A.; Michel, P. 2021. Conservation status of birds in Aotearoa New Zealand birds, 2021. New Zealand Threat Classification Series 36. Wellington, Department of Conservation. 43p.

Smithers, B.V.; Peck, D.R.; Krockenberger, A.K.; Congdon, B.C. 2003. Elevated sea-surface temperature, reduced provisioning and reproductive failure of wedge-tailed shearwaters (Puffinus pacificus) in the southern Great Barrier Reef, Australia. Marine and Freshwater Research 54: 973-977.

Taylor, G. 2000. Action Plan for Seabird Conservation in New Zealand. Part B: non-threatened seabirds. Threatened Species Occasional Publication No.17. Department of Conservation. Wellington.

Tennyson, A.J.D. 2010. Procellariiformes. Pp. 64-135. In: Checklist Committee (OSNZ) 2010. Checklist of the birds of New Zealand, Norfolk and Macquarie Islands, and the Ross Dependency, Antarctica (4th edn). Ornithological Society of New Zealand & Te Papa Press, Wellington.

Veitch, C.R.; Miskelly, C.M.; Harper, G.A.; Taylor, G.A.; Tennyson, A.J.D. 2004. Birds of the Kermadec Islands, south-west Pacific. Notornis 51: 61-90.

Veitch, C.R.; Gaskin, C.; Baird, K.; Ismar, S.M.H. 2011. Changes in bird numbers on Raoul Island, Kermadec Islands, New Zealand, following the eradication of goats, rats, and cats. Pp 372-377 In Veitch, C.R.; Clout, M.N.; Towns, D.R. (eds) Island invasives: eradication and management. Proceedings of the International Conference on Island Invasives. Gland, Switzerland: IUCN.

Recommended citation

Szabo, M.J. 2013 [updated 2023]. Wedge-tailed shearwater. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz