Ashy Storm Petrel

The Ashy Storm Petrel, Hydrobates homochroa, presents itself as a small seabird with a uniform sooty-brown plumage. Its name, derived from the Greek words for "alike" and "color," aptly describes its subtle coloration. This species is recognized by its forked tail and diminutive stature.

Identification Tips

When observing the Ashy Storm Petrel, one may note its smaller size compared to the similar Black Storm Petrel. Its flight is characterized by a distinctive fluttering motion, with the upstroke halting horizontally to the body before the downstroke commences—a trait setting it apart from other storm petrels in its range.

Habitat

This bird favors the open ocean, where it spends the majority of its life, only coming ashore to breed on rocky islands.

Distribution

The Ashy Storm Petrel breeds on a select number of islands off the coasts of California and Mexico, with a significant portion of the global population nesting on the Farallon Islands near San Francisco. Other notable breeding sites include the Channel Islands of California and Mexico's Coronados.

Behaviour

The Ashy Storm Petrel is a nocturnal feeder, often seen in groups at sea. It shows remarkable fidelity to both its mate and nesting site, returning to the same burrow year after year, despite spending the non-breeding season apart from its mate.

Song & Calls

The vocalizations of the Ashy Storm Petrel are less documented in this guide, but like its relatives, it likely has a repertoire of calls used in social interactions at sea and near nesting sites.

Breeding

Breeding occurs in rock burrows on offshore islands, with a protracted cycle that includes egg-laying in May and fledging in October. Timing can vary significantly among pairs.

Similar Species

The Black Storm Petrel is similar in appearance but can be distinguished by its larger size and different flight pattern.

Diet and Feeding

The diet consists of cephalopods, fish, particularly deep-sea myctophids, and euphausiid krill like Thysanoessa spinifera. These prey items rise to the ocean's surface at night, making them accessible to the petrels. The birds are also known to follow fishing vessels for fish oils released from nets.

Conservation status

The Ashy Storm Petrel is classified as Endangered, with an estimated global population of around 10,000 birds. Threats include predation by gulls and owls, light pollution from boats, introduced predators, and environmental changes due to global warming and ocean acidification. Conservation efforts are in place on most breeding islands to protect this species.