Wedge-tailed Shearwater

The Wedge-tailed Shearwater, Ardenna pacifica, is a medium-large member of the seabird family Procellariidae. It exhibits two distinct color morphs: pale and dark. The pale morph, more common in the North Pacific, has grey-brown upperparts and a white underside, while the dark morph, prevalent elsewhere, is uniformly grey-brown. This species is named for its distinctive large, wedge-shaped tail, which aids in gliding. It has a dark bill and salmon pink legs, which are positioned far back on the body, an adaptation for efficient swimming.

Identification Tips

To identify the Wedge-tailed Shearwater, look for its large size among tropical shearwaters, the wedge-shaped tail, and the color morphs. The pale morph has contrasting grey-brown and white plumage, whereas the dark morph is uniformly dark. The bill is black, and the legs are a notable salmon pink.

Habitat

This shearwater is pelagic, spending most of its life at sea. It comes ashore only to breed, nesting in colonies on small tropical islands.

Distribution

The Wedge-tailed Shearwater is found throughout the tropical Pacific and Indian Oceans, within roughly 35°N and 35°S latitude. It breeds on islands off Japan, the Islas Revillagigedo, the Hawaiian Islands, the Seychelles, the Northern Mariana Islands, and along the eastern and western coasts of Australia.

Behaviour

This species is monogamous, often forming long-lasting pair bonds. It exhibits natal philopatry, with individuals returning to their birth colony to breed. The Wedge-tailed Shearwater is nocturnal at breeding colonies but may be seen during the day when not breeding. It is known for its distinctive moaning call, which serves both to maintain pair bonds and to deter intruders.

Song & Calls

The call of the Wedge-tailed Shearwater is a long, moaning sound with an inhaling component ("OOO") and exhaling component ("err"), which has earned it the Hawaiian name 'ua'u kani, meaning "moaning petrel."

Breeding

Breeding seasons vary by hemisphere, with synchronised breeding more common at higher latitudes. The species is known for its burrow or surface nesting under cover, and both sexes share in incubation and chick rearing. A single egg is laid per season, and chicks are fed a rich stomach oil and solids until they fledge after 103–115 days.

Similar Species

The closely related Buller's Shearwater, also with a wedge-shaped tail and thin black bill, can be distinguished by its different color pattern.

Diet and Feeding

The Wedge-tailed Shearwater feeds pelagically on fish (notably goatfish), squid, and crustaceans. It was once thought to feed mostly at the surface, but has been observed diving to depths of up to 66 meters (217 feet) to forage.

Conservation status

The IUCN lists the Wedge-tailed Shearwater as Least Concern, indicating that it is not currently at significant risk of widespread decline.