ʻUaʻu Kani - Wedge-tailed Shearwater

Species Information

The ‘ua‘u kani or wedge-tailed shearwater is a large, abundant seabird (Family: Procellaridae) that produces a variety of wails and moans that surely inspired the Hawaiian name of this bird which means “calling or moaning petrel.” Individuals have long thin wings, a wedge-shaped tail, and a hooked bill. ‘Ua‘u kani (wedge-tailed shearwater) are polymorphic, having two color phases, dark or light, and sexes are similar. Light-phase adults are grayish brown above with white underparts except for dark trailing edges of wings and tail. Dark-phase adults are uniformly sooty brown. Flight is similar to that of albatross but flaps wings with greater frequency. Often forages in large, mixed-species flocks associated with schools of large predatory fishes which drive prey species to the surface. ‘Ua‘u kani (wedge-tailed shearwater) use a variety of foraging techniques, most frequently plunges head into the water while on the wing, also seizes prey will sitting on the water; often follows fishing vessels. In Hawai‘i, diet primarily consists of larval goatfish, flyingfish, squirrelfish, and flying squid. Like most seabirds ‘ua‘u kani (wedge-tailed shearwater) breed in their natal colonies, form long-term pair bonds (although breeding failure in this species may result in divorce), have high site fidelity, lay only one egg per season, and both parents participate in all aspects of raising young. ‘Ua‘u kani (wedge-tailed shearwater) excavate burrows or nest in rock cervices. In Hawai‘i, breeding is very synchronous, and most eggs are laid in June with most young fledging in November. Birds first breed at four years of age, and the oldest known individual was 29 years old.

Distribution & Abundance

ʻUa‘u kani (wedge-tailed shearwater) breed throughout the NHWI and on offshore islets of most of the MHI. Outside of Hawai‘i, ‘ua‘u kani (wedge-tailed shearwater) breeds on islands throughout the tropical and subtropical Indian and Pacific oceans. Outside the breeding season, ‘ua‘u kani (wedge-tailed shearwater) migrate to the eastern Pacific.

In Hawai‘i, the population is estimated at 270,000 breeding pairs with the largest colonies occurring on Laysan (125,000 - 175,000 pairs), Nihoa (30,000 - 40,000 pairs), and Lisianski (10,000 - 30,000 pairs). The population in the MHI is estimated at between 40,000 and 60,000 breeding pairs with the largest colonies occurring on the offshore islands of Mānana (10,000 - 20,000 pairs), Moku Loa (10,000 - 20,000 pairs), Lehua (23,000 pairs), and Ka‘ula (1,500 - 2,500 pairs). Smaller populations occur on Moku Manu, Moku‘auia, Kāpapa, Molokini, Photo: Forest and Kim Starr, USFWS Hawaii’s Comprehensive Wildlife Conservation Strategy October 1, 2005, Mōkapu Peninsula, Ka‘ena Point Natural Area Reserve on O‘ahu, and Kīlauea Point National Wildlife Refuge on Kaua‘i. Worldwide population is estimated at over one million breeding pairs.

Location & Condition of Key Habitat

Terrestrial: ‘Ua‘u kani (wedge-tailed shearwater) breed on low, flat islands and sand spits with little or no vegetation, but also excavate burrows on the slopes of extinct volcanoes and in old volcanic craters. Burrows require firm soil or plant roots to stabilize loose soil, generally nesting habitat is devoid of tall woody plants. In locations where nest sites are scarce or the ground is too hard to excavate burrows individuals will nest in rock crevices or above ground.

Marine: Pelagic.


Introduced predators

Like all seabirds, adults and nests are susceptible to mammal predation by pigs (Sus scrofa), rats (Rattus spp.), feral cats (Felis silvestris), and the small Indian mongoose (Herpestes auropunctatus).

Human disturbance

Laysan (Telespiza cantans) and Nihoa (T. ultima) finches will depredate eggs left unattended because of human disturbance. Trampling by humans will collapse burrows.

Artificial lighting

Street and resort lights, especially in coastal regions, disorient fledglings causing them to eventually fall to the ground exhausted or increasing their chance of collision with artificial structures (i.e. fallout). Once on the ground, fledglings are unable to fly and are killed by cars, cats, and dogs or die because of starvation or dehydration.


Because ‘ua‘u kani (wedge-tailed shearwater) rely on predatory fish to drive prey to the surface, overfishing may eventually affect Hawaiian populations.


Mercury, lead, and organochlorines have been detected in Hawaiian birds.


Pox-like lesions have been observed on birds breeding on Maui and Moloka‘i.