StatusCassin's auklet is listed as Near Threatened, and some populations have suffered steep declines. Threats to the auklet include introduced carnivores , oil spills and changes in sea surface temperature . Cassin's auklet is protected under the Migratory Bird Treaty Act of 1918. Annual variation in ocean climate synchronously affects multiple demographic parameters including survival, breeding propensity, breeding success, and recruitment, a situation conducive to rapid population declines due to climate change.
BehaviorCassin's auklet nests in burrows on small islands, and in the southern area of its range may be found in the breeding colony year round. It either digs holes in the soil or uses natural cracks and crevices to nest in, also readily using man-made structures. Pairs will show a strong loyalty towards each other and to a nesting site for many years. Both the parents incubate the single white egg, returning to swap shifts at night to avoid being taken by predators such as the western gull or peregrine falcon. They also depart from the colony before dawn. The egg is incubated for 40 days, the small chick is then fed nightly for 35 days by both parents, who regurgitate partially digested food carried in a special gular pouch, often referred to in the literature as a sublingual pouch. The chick fledges alone and makes its way to the sea. Cassin's auklet is unusual amongst seabirds in occasionally laying a second clutch after a successful first clutch .
Most individuals in a cohort begin breeding at age 3 , and by 8 years >95% of a given cohort has recruited. Mean age of recruitment is 3.6 years. Minimum annual breeding propensity is 0.83, apparent local survival is 0.76, juvenile survival is 0.15.
At sea Cassin's auklets feeds offshore, in clear often pelagic water, often associating with bathymetric landmarks such as underwater canyons and upwellings. Numbers at sea may be grossly underestimated because the bird moves away from ships at a distance of more than a kilometer. Recently their distribution around Triangle Island has been determined by telemetry. It feeds by diving underwater beating its wings for propulsion, hunting down large zooplankton, especially krill. It can dive to 30 m below the surface, and by some estimates 80 m.
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