NATURAL HISTORY

XANTUS’S MURRELET } Synthliboramphus hypoleucus
FAMILY: Alcidae

DESCRIPTION: This robin-sized seabird is black above and white below with incomplete white eye-rings, a short tail, black legs and feet, and a narrow black bill. Xantus’s murrelets measure less than 10 inches in length, have a 15-inch wingspan, and weigh only six ounces. They can be distinguished in flight from the similar Craveri’s murrelet by their white underwings.

HABITAT: Xantus’s murrelets nest during the breeding season in the natural rock crevices, cliffs, and canyons found on offshore islands. The rest of the year, these birds leave the islands and move out to sea, concentrating in deep waters beyond the continental shelf.

RANGE: The Xantus’s murrelet lives off the west coast of North America, with a range primarily stretching from Southern California to central Baja California, Mexico. It spends the majority of its life at sea, nesting for a few months of the year on offshore islands including the Channel Islands, Santa Barbara Island, and Los Coronados Islands.

MIGRATION: Once the breeding season ends, Xantus’s murrelets move out to sea. They occasionally wander as far north as British Columbia, Canada. This dispersal is not considered a true migration.

BREEDING: Nesting on offshore islands occurs between February and July; however, no actual nest is constructed. A clutch of two eggs, often mottled with walnut-brown and cinnabar spots, is laid on the ground in a rock crevice and incubated for a little more than a month by both parents. Murrelet chicks hatch with their eyes open and are covered with down. At just two days old, they depart the nest at night to follow their parents’ whistling calls, tumble down cliffsides, and jump into the ocean surf. They are reared by their parents at sea and stay with their families for several months.

LIFE CYCLE: Murrelets live at least 15 years.

FEEDING: These seabirds feed in deep ocean waters on larval fish like anchovies and sardines, as well as small crustaceans and various aquatic invertebrates. Murrelets are wing-propelled divers, flying underwater after prey with powerful, rapid wingbeats. They are regularly observed feeding cooperatively in pairs rather than flocks.

THREATS: Threats to the Xantus’s murrelet include predation from introduced cats and rodents, oil spills and water pollution, artificial light pollution from fishing vessels and offshore energy terminals, increased shipping traffic, incidental bycatch, climate change, and proposed liquid natural gas facilities.

POPULATION TREND: During the last century, the already small range of the Xantus’s murrelet shrank as nonnative predators eliminated the species entirely from some nesting sites and drastically reduced murrelet numbers in others. The largest nesting colony in California experienced a 30-percent decline from 1977 to 1991. In recent years, efforts to remove introduced predators have resulted in population rebounds in some locations. Yet overall population size is still perilously low, and the population trends of the largest breeding colony are still negative. Human activities continue to threaten the remaining population, estimated at 8,000 to 18,000 breeding birds worldwide.

Photo by Stonebird via Flickr Commons