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Ashy Storm-Petrel
Oceanodroma homochroa
– Family
Authors: Ainley, David

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Flock of Ashy Storm-Petrels in Monterey Bay, CA.
Figure 1. Distribution of the Ashy Storm-Petrel.

Among the four, all-dark storm-petrel species nesting on islands along the west coast of North America, the Ashy Storm-Petrel is the most northern. Confined to California islands and nearby waters, this species is a smoke-gray color that befits its foggy environment. Like other storm-petrels, the Ashy Storm-Petrel arrives and departs its breeding colonies only at night; unlike most others, it undertakes no migrations or expansive postbreeding dispersions. Rather, Ashy Storm-Petrels frequent their nesting islands for most of the year and feed nearby in offshore waters of the California Current, one of the richest regions of the world ocean.

Like other members of the order, each pair of reproductively active Ashy Storm-Petrels produce only a single egg in any reproductive season. Unlike other storm-petrels that migrate and lay eggs in synchrony with other colony members, the Ashy Storm-Petrel spreads out its egg-laying over several months. Periods of incubation and chick growth are each very long by avian standards. The chicks of some pairs can be half grown at the time when other pairs lay their egg. Consistent with the extended occupation of the colony and the prolonged nesting duties, molt in the Ashy Storm-Petrel overlaps broadly with breeding, differing from the segregated molt schedules of migratory tube-nosed seabirds.

The entire world breeding population of the Ashy Storm-Petrel is estimated to be on the order of 10,000 birds. Populations of predatory gulls have grown immensely in recent decades, and rodents, which also are predators against which storm-petrels have no defense, have invaded the larger islands where this storm-petrel nests, or formerly did so.

These factors do not bode well for positive growth or stability in populations of the Ashy Storm-Petrel. Nesting colonies, however, are distributed among at least 17 localities, almost all of which are protected at least from the direct encroachment of human civilization.