NATURAL HISTORY

ASHY STORM PETREL } Oceanodroma homochroa
FAMILY: Hydrobatidae

DESCRIPTION: Ashy storm petrels are smoke-gray seabirds with shallowly forked tails and long, slender wings. Males and females are similar, measuring approximately seven inches in length and typically having a 16-inch wingspan. A pale gray wash on their underwings creates a distinct bar, which is useful for identification. Rarely gliding, ashy storm petrels fly with short, shallow, fluttering wing beats. They have dark-colored bills with a prominent horny tube at the base.

HABITAT: Ashy storm petrels nest in the natural rock crevices found on offshore islands. At sea, the petrels live within the California Current System, preferring the near-shore waters of the continental slope.

RANGE: Ashy storm petrels inhabit the coastal waters off central California, south to northern Baja California, Mexico. Their breeding range is restricted to six offshore island groups and several groups of offshore rocks. Almost the entire breeding population nests on the South Farallon Islands and the Channel Islands.

MIGRATION: Non-migratory seabirds, ashy storm petrels don’t range as far as other species of storm petrel. During fall and winter, birds disperse slightly to offshore waters.

BREEDING: Nesting in large colonies, ashy storm petrels lay eggs throughout a breeding season that can start as early as March and last as long as October. They are pelagic birds who only come ashore to breed. Breeding pairs use burrows excavated by other seabirds, natural crevices, and holes in human-constructed rock walls. Females lay only one egg, which is incubated by both sexes for about 45 days. Chicks are fed regurgitated food and leave the nest in three months. Ashy storm petrels have the same mate for many years and repeatedly nest in the same burrow.

LIFE CYCLE: Ashy storm petrels are known to live for at least 25 years.

FEEDING: Ashy storm petrels make use of the abundant surface food provided by upwellings of the California Current System. They feed by night, catching small fish and plankton.

THREATS: Major threats to ashy storm petrels include decreased food supply due to rising ocean temperatures and acidification, habitat loss from rising sea levels, artificial light pollution from fishing vessels and offshore energy terminals, contaminants that cause eggshell thinning, oil spills, depredation by introduced and native predators, and plastic ingestion.

POPULATION TREND: Between 1972 and 1992, the largest colony of ashy storm petrels decreased by nearly half. Reproductive success has also dramatically declined in the past three decades. Today, there are an estimated 5,400 breeding birds remaining.

 

Photo by Glen Tepke