Wedge-tailed shearwater (Puffinus pacificus)

Description

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Wedge-tailed shearwater fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Wedge-tailed shearwater description

The largest of the tropical shearwaters, the wedge-tailed shearwater (Puffinus pacificus) has a slender body and long, thin wings. Named for the way in which shearwater species hold their wings motionless as they glide and skim or ‘shear’ the water during flight, the wedge-tailed shearwater also derives its common name from its characteristically wedge-shaped tail ^{(2) (3)}. The legs of the wedge-tailed shearwater are positioned far back on its body, giving it an odd, forward-tipped posture when on land ⁽²⁾.

The wedge-tailed shearwater exists in two different colour morphs: a light morph and a dark morph ^{(2) (3) (4)}. Occasionally, some individuals may appear intermediate between the two. The dark morph has sooty-brown upperparts, with the feathers of the back and wings edged in slightly lighter brown. The primaries and undertail-coverts are black. The chin, throat and forehead are brownish-grey, and the underparts are generally dusky brown ^{(2) (3) (5)}. The light morph wedge-tailed shearwater is greyish-brown above with white underparts, except for thick dark bands on the underside of the wings and dark undertail-coverts ^{(2) (3)}. The sides, flanks and undertail may sometimes appear mottled grey-brown ^{(3) (6)}.

Both morphs of the wedge-tailed shearwater have a pinkish to dark grey bill and flesh-coloured legs ^{(2) (5) (7) (8)}. In general, the pale morph predominates in the North Pacific but the dark morph is more prominent throughout the rest of the wedge-tailed shearwater’s range ^{(2) (3)}. 

The wedge-tailed shearwater emits an eerie, wailing call from its burrow during the night, comprising of an inhaling component, ‘OOO’, and an exhaling component ‘errr’. This ghost-like sound gives rise to the Hawaiian name for this species, ‘ua’u kani’, which means ‘calling or moaning petrel’ ^{(2) (3)}.

French

Puffin du Pacifique.

Size

Length: c. 43 cm ⁽²⁾

Adult weight: c. 390 g ⁽²⁾

Juvenile weight: 430 - 560 g ⁽³⁾

Wedge-tailed shearwater biology

A mostly pelagic species, the wedge-tailed shearwater forages over large tracts of open ocean where it feeds mainly on fish, although cephalopods, crustaceans and insects may also be taken ^{(2) (7) (9) (10)}. It generally feeds during the day, often aggregating in feeding flocks associated with tuna and other large predatory fish, or congregating around other seabirds, dolphins, trawlers or fishing boats ^{(2) (9) (10)}.

The wedge-tailed shearwater catches its prey primarily by ‘contact-dipping’, where the bird flies close to the surface and plunges the head and neck into the water to capture prey during flight. Having seized a fish or other prey item, the wedge-tailed shearwater flips the head upwards to swallow the prey mid-flight. The wedge-tailed shearwater may also sit on the water surface to feed, and will sometimes make deeper dives, to a maximum depth of 66 metres below the surface ^{(2) (7)}.

The wedge-tailed shearwater breeds between February and November in the Northern Hemisphere and September to June in the Southern Hemisphere, although the exact timing varies with location ^{(2) (3) (10)}. The wedge-tailed shearwater is monogamous and generally returns to the colony in which it was born to breed, often reclaiming the same nest site from season to season ^{(2) (3) (12) (13)}.

The nest site is selected by both the male and female wedge-tailed shearwater as part of the courtship ritual. Nests are usually close to sea level, in burrows in sand or soil. It may also nest in rock crevices and caves, or will sometimes nest on the surface under dense vegetation ^{(2) (1)}. Both adults contribute to the excavation of the burrow, digging using the bills and feet to loosen, scrape and remove the soil ^{(2) (3)}. The first part of the burrow generally slopes downwards towards a nesting chamber which is often, but not always, lined with vegetation ⁽²⁾. Mating takes place either in or near the burrow once the nest is complete, after which both members of the breeding pair will return to sea for up to a month to forage, building up energy reserves for egg-laying and incubation ^{(2) (3) (11) (12)}.

The wedge-tailed shearwater lays a single, very large white egg which is incubated for between 50 and 53 days. Both adults share the incubation duties in alternating shifts that last up to 13 days at a time, with the male generally incubating first ^{(2) (3) (11) (13)}. After hatching, the chick is brooded for up to six days, after which it is left alone while the adults hunt. The chick is initially fed by the adults with stomach oil, an energy-rich, waxy oil of digested prey, before eventually being fed whole fish ⁽³⁾. Wedge-tailed shearwater chicks grow much larger than the adults during the nestling period, increasing to a weight of around 560 grams before dropping to around 430 grams. The chick remains in the burrow for the whole of the nestling period but is generally deserted by the adult wedge-tailed shearwaters a few weeks before fledging, which typically occurs after 103 to 115 days ^{(2) (3)}.

Wedge-tailed shearwater range

The wedge-tailed shearwater is widely distributed across the tropical Pacific and Indian Oceans ^{(3) (9)}.

In the Indian Ocean, the wedge-tailed shearwater breeds from the west coast of Madagascar, to the Seychelles in the north, Cocos Islands in the east and Reunion Island in the south. It also breeds on the east and west coasts of Australia ^{(2) (9)}.

In the North Pacific, the wedge-tailed shearwater breeds on Pescadores, Bonin Island, Volcano Island, Marshall Island and Caroline Island, to the east coast of Mexico. In the Central Pacific, breeding sites include Johnston Atoll and Christmas Island. The wedge-tailed shearwater also breeds on islands throughout the South Pacific as far south as Lord Howe Island and as far east as the Pitcairn Islands ⁽²⁾. It has occasionally been recorded breeding as far east as Panama and Ecuador ⁽⁵⁾.

Wedge-tailed shearwater habitat

The wedge-tailed shearwater typically nests on low, flat islands, sand spits or atolls with little or no vegetation ^{(2) (9)}.

Wedge-tailed shearwater status

The wedge-tailed shearwater is classified as Least concern on the IUCN Red List ⁽¹⁾.

Wedge-tailed shearwater threats

The wedge-tailed shearwater has a wide distribution and a large estimated population. However, in some areas the population is suspected to be in decline owing to changes to the shearwaters’ food supply, such as declining tuna stocks through the over-exploitation of tuna fisheries ^{(9) (10) (14)}. In addition, unsustainable levels of exploitation of the wedge-tailed shearwater through poaching or persecution are likely to impact some populations ^{(2) (10) (14)}. As a ground nesting species it is also particularly vulnerable to predation by invasive species, including rats, cats and pigs, which predate on the adults, chicks and eggs of this species ^{(10) (14)}.

The burrows of the wedge-tailed shearwater are prone to collapse, especially where habitat is degraded, either naturally through the prevailing weather causing erosion or damage, or by human disturbance and trampling around nest sites. Burrows are also commonly inundated with water from heavy rainfall or excessively high tides, which may cause nest failure and reduced breeding success in affected colonies ^{(2) (13)}.

Another common threat to wedge-tailed shearwater fledglings in particular is their attraction to street lights and other bright lights. The young birds become confused and disorientated, and are frequently reported colliding with power lines and other objects ^{(2) (11)}.

Wedge-tailed shearwater conservation

The wedge-tailed shearwater is not currently listed on any conservation legislation, although it has been identified as a potential candidate for listing on the Agreement on the Conservation of Albatrosses and Petrels ⁽¹⁴⁾. The wedge-tailed shearwater is also included on the Migratory Bird Treaty Act in the United States, which prohibits taking of protected species, their nests and eggs except as permitted by regulation ⁽¹⁵⁾.

Future conservation measures to ensure that populations of the wedge-tailed shearwater remain stable may include maintaining predatory fish, squid, and bait fish stocks, controlling predators, preventing destruction of burrows and habitat, and managing vegetation around breeding colonies ⁽²⁾.

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

Find out more

Find out more about the wedge-tailed shearwater:

• Whittow, G.C. (1997) Wedge-tailed shearwater (Puffinus pacificus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
  http://bna.birds.cornell.edu/bna/species/305
• Harper, P.C. and Kinsky, F.C. (1974-5) New Zealand albatrosses and petrels: an identification guide. Tuatara, 21(1 and 2): 1-80. Available at:
  http://www.nzetc.org/tm/scholarly/tei-Bio21Tuat01-02.html

Find out more about the wedge-tailed shearwater and other birds:

• BirdLife International:
  http://www.birdlife.org/

Find out more about the conservation of albatrosses and petrels:

• Agreement on the Conservation of Albatrosses and Petrels:
  http://www.acap.aq/

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Glossary

Cephalopod

From the Greek for ‘head-foot’, a class of molluscs that occur only in marine habitats. All species have grasping tentacles, and either an internal or external shell. Includes nautiloids, cuttlefish, squids, octopuses, and extinct ammonites and belemnites.

Coverts

Small feathers concealing the bases of larger flight feathers, usually on the wings or tail.

Crustaceans

Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Incubate

To keep eggs warm so that development is possible.

Incubation

The act of incubating eggs, that is, keeping them warm so that development is possible.

Monogamous

Having only one mate during a breeding season, or throughout the breeding life of a pair.

Morph

One of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).

Pelagic

In birds, applied to sea birds that come to land only to breed, and that spend the major part of their lives out at sea.

Primaries

In birds, the main flight feathers projecting along the outer edge of the wing.

References

1. IUCN Red List (March, 2011)
   http://www.iucnredlist.org/
2. Whittow, G.C. (1997) Wedge-tailed shearwater (Puffinus pacificus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
   http://bna.birds.cornell.edu/bna/species/305
3. MobileReference. (2008) The Illustrated Encyclopedia Of North American Birds: An Essential Guide To Birds Of North America. MobileReference, Boston.
4. Davis Jr, W.E. (2006) Plumage dimorphism in Wedge-tailed shearwaters Puffinus pacificus in Shark Bay, Western Australia. Journal of Field Ornithology, 77(1): 92.
5. Ridgely, R.S. and Gwynne, J.A. (1989) A Guide to the Birds of Panama: With Costa Rica, Nicaragua, and Honduras. Princeton University Press, Princeton, New Jersey.
6. Dunn, J. and Alderfer, J.K. (2006) National Geographic Field Guide to the Birds of North America. National Geographic Books, Washington.
7. Hilty, S.L. and Brown, B. (1986) A Guide to the Birds of Colombia. Princeton University Press, Princeton, New Jersey.
8. Harper, P.C. and Kinsky, F.C. (1974-5) New Zealand albatrosses and petrels: an identification guide. Tuatara, 21(1 and 2): 1-80. Available at:
   http://www.nzetc.org/tm/scholarly/tei-Bio21Tuat01-02.html
9. BirdLife International - Wedge-tailed shearwater (March, 2011)
   http://www.birdlife.org/datazone/speciesfactsheet.php?id=3928
10. Burger, A.E. and Lawrence, A.D. (2001) Census of wedge-tailed shearwaters Puffinus pacificus and Audubon’s shearwater P. lherminieri on Cousin Island, Seychelles using call-playback. Marine Ornithology, 29: 57-64.
11. Offshore Islet Restoration Committee - Wedge-tailed shearwater (March 2011)
    http://www.hawaiioirc.org/OIRC-SPECIES-BIRDS.htm
12. Perrins, C. (2003) The Encyclopedia of Birds. Oxford University Press, Oxford.
13. Bancroft, W.J., Roberts, D. and Garkaklis, M.J. (2005) Burrow entrance attrition rate in wedge-tailed shearwater Puffinus pacificus colonies on Rottnest Island, Western Australia. Marine Ornithology, 33: 23-26.
14. Agreement on the Conservation of Albatrosses and Petrels (March, 2011)
    http://www.acap.aq/latest-news/research-on-wedge-tailed-shearwaters-2000-2010
15. Migratory Bird Treaty Act (March, 2011)
    http://www.fws.gov/laws/lawsdigest/migtrea.html