Cassin's Auklet (Ptychoramphus aleuticus)
This secretive species is the most abundant seabird breeding in British Columbia. Living on the open ocean, it only comes ashore under the cover of darkness to nest. As it prefers small offshore islands, far away from human interference, it is difficult to study.
With a maximum length of 18 cm, this small bird is hard to spot on the water due to the dark grey colour of its upper body and wings. In flight, however, its white abdomen and undertail coverts are evident. Up close, a small white spot over each eye and white colouration at the base of the lower jaw is visible. Its stout bill is black and the upper surface of its legs and toes is bright blue. This is the only small Pacific diving bird with a dark coloured throat during the winter.
Cassin's auklet has an extensive range covering most of the North American Pacific coastline. This bird is pelagic, only coming ashore for breeding, congregating on the islands of northern British Columbia and Alaska. The largest colony, consisting of 360,000 pairs, is found on Triangle Island, British Columbia.
Cassin's auklets risk their lives to nest, digging long narrow burrows that may take several days to complete. The risk of predation by bald eagles is great during construction of the burrow. Because of the large size of each egg - 16% of a female's body weight - only one egg is laid per season. Both parents take turns incubating, for up to 38 days. The young remains in its burrow until taking flight 41 days later.
Both parents are involved in feeding the offspring. Shortly before each breeding season, a special pouch develops inside the throat of Cassin's auklets. This gular sac is used to carry food, such as crustaceans or small fish, back to the nest. The contents of the pouch are referred to as soup and have a powerful odour. This odour, and the purple spattering of the soup at the mouth of burrows, are clear indications of aCassin's auklet colony.
Cassin's auklets are swift underwater predators that use their wings as paddles. In late spring and early summer, oil-rich fishes such as capelin, are a choice food, but their staple diet consists of small shrimp-like crustaceans. Unfortunately for these birds, this is the same food eaten by baleen whales, such as humpbacks. Occasionally, an auklet is accidentally ingested in a large mouthful!