Introduction

The Wedge-tailed Shearwater is a pelagic seabird of the tropical and subtropical Pacific and Indian Oceans. The wailing sounds that shearwaters make sitting in or near their burrows during the night have given rise to their Hawaiian name, which means “calling or moaning petrel.” Characteristically, this species nests on small islands, laying its single white egg in a burrow in the ground. It is a dusky brown bird with a musky odor to its feathers; white breast-feathers are visible in some forms. Wedge-tailed Shearwaters are polymorphic: There are dark, light, and intermediate forms. The light and dark morphs bear no relation to age, sex, or breeding status. In the air, the irregularly white undersurfaces of the wings are apparent in birds with light plumage; so also is the wedge-shaped tail from which the species derives its name. The wings are long and thin; shearwaters are named for the way in which their motionless wings skim (shear) the water in gliding flight.

Shearwaters feed offshore, by “contact-dipping” with their long, slender bills. The placement of the legs far back on the body is adaptive to swimming underwater but, for the same reason, Wedge-tailed Shearwaters appear awkward on land, waddling rather than walking. They feed mainly on larval forms of fish such as goatfish and flying fish, and they feed mostly during the day in association with skipjack tuna and other predatory fish.

Wedge-tailed Shearwaters breed from Madagascar in the western Indian Ocean to the Revillagigedo Is. in the eastern Pacific, off Mexico. Males and females share the digging or renovation of the burrow and mate in or near it. After mating, both members of the pair return to sea for up to 4 weeks. This prelaying exodus allows the female to feed while developing the egg. Egg-laying is synchronous in Wedge-tailed Shearwater colonies; both members of the pair share the long incubation spells. The egg is relatively large and the incubation period long. Shearwater nestlings grow to exceed the body mass of the adults, but they are deserted by the parents several weeks before fledging.

The Wedge-tailed Shearwater is long-lived and is one of the most abundant species of seabirds in the Hawaiian Islands.