Ainley's storm petrel (Hydrobates cheimomnestes ) is a species of seabird in the family Hydrobatidae. It breeds in the winter on Guadalupe Island off the western coast of Mexico. It ranges south to the Galápagos Islands. It is considered by some authorities to be a subspecies of the Leach's storm petrel.
Ainley's storm petrel is a medium-sized species about 18 cm (7.1 in) long, with fairly long wings with blunt points, and a moderately long, forked tail. The general colour is dark sooty-brown but from a distance this appears black; pre-moult adults may look more brownish when the plumage is worn. The rump is white, a U-shaped white patch having a central poorly defined dark area. The beak, legs and feet are black, and the feet do not extend beyond the tail in flight.
This bird spends much time away from land over open ocean where its habits are likely to be similar to Leach's storm petrel (Hydrobates leucorhoa ). During the breeding season it occurs on the waters off the Baja California Peninsula. It is only known to breed on three islets off the southern end of Guadalupe Island, Mexico. At the breeding colonies, this bird is nocturnal. It nests in crevices and burrows, and the total world population probably does not exceed a few thousand birds.
