Craveri's Murrelet or Cassin's Auklet?

General appearance

The Cassin's Auklet is a small, plump bird with a length ranging from 19 to 25 cm. This seabird exhibits a stocky build and short wings. Its plumage is predominantly gray with a darker tone on the upper side, while the underparts are lighter gray. The face is marked by a small white crescent above the eye, and the cheeks bear a slightly lighter patch. Its bill is short and stout, appearing black, and its legs and feet tend to exhibit a bluish-gray tone.

Male vs female

Cassin's Auklets show very little sexual dimorphism, meaning males and females look very similar. Both sexes sport identical coloration and size, which makes it challenging to differentiate them in the field. Observation of breeding behavior is generally necessary for accurate identification between males and females.

Juvenile

Juvenile Cassin's Auklets resemble adults but display a few key differences. Their plumage is slightly duller with a more uniform gray tone, lacking some of the sharp contrast seen in adults. The white crescent above the eye may not be as pronounced, and the bill is smaller and less robust, appearing paler in hue. As juveniles mature, they gradually acquire the definitive adult plumage.

Primary Habitat

Cassin's Auklet primarily inhabits the cool, coastal waters off the Pacific coast of North America, ranging from Alaska to Baja California. It prefers open seas and offshore islands, nesting in burrows dug into grassy slopes or sandy soil near the shore. The bird thrives in cold water climates, often dependent on upwelling zones rich in marine food resources.

Additional Range

While less common, the bird occasionally enters more temperate waters further offshore during non-breeding seasons. It also exhibits a degree of adaptability by nesting on islands with varying vegetative cover, demonstrating its flexibility to thrive in diverse environmental conditions.

Natural Diet

Cassin's Auklet, scientifically recognized as Ptychoramphus aleuticus, has a diet that predominantly consists of small marine creatures. These adept seabirds primarily feast on zooplankton, including copepods, krill, and small fish. Their feeding patterns may demonstrate seasonal variation, with krill becoming more significant in their diet during periods of abundance, typically in spring and early summer. These seabirds rely on dense swarms of these small sea creatures that occur due to ocean currents and upwellings. During winter months, when food availability decreases, Cassin's Auklets may extend their range in search of sufficient nourishment.

Bird Feeders

Cassin's Auklets are not commonly seen at bird feeders and typically do not consume standard feeder offerings. These seabirds are highly adapted to their marine environment and their diet consists mainly of natural resources found in oceanic habitats. Thus, they do not show interest in foods such as seed mixes, suet, or fruits that are often provided by backyard bird feeders. As these birds are primarily pelagic, they rarely come into contact with typical feeder setups found on land. Encouraging the presence of Cassin’s Auklets is best achieved through conservation of their natural marine habitats rather than offering supplemental feeder food.