Biology of Nesting Ancient Murrelets

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Abstract
The breeding biology of ancient murrelets [Synthliboramphus antiquus] was studied on and near Langara Island, Queen Charlotte Islands, British Columbia [Canada]. Adults and subadults were not sexually dimorphic in size or plumage characters, sex ratios approach equality, and mate retention and nest site tenacity prevailed. Two age categories, adult and subadult, were identifiable. The partial prealternate molt and prebasic molt did not overlap breeding. Adults returned to the vicinity of Langara Island in mid-March and began to visit the colonies in early April. The birds were nocturnal on the nesting slopes. Two-egg clutches were usual, with each egg weighing .apprx. 22% adult weight. The eggs were laid .apprx. 7 days apart. Incubation shifts were 72 h over the 35 day incubation period. The young were truly precocial and left the nest burrows 2 days after hatching. The major predator on adult ancient murrelets on Langara Island was the peregrine falcon. Predation on adults, eggs and young by the introduced black rat seemed negligible in the colonies where and when observations were made. The adaptive significance of precocity in alcids is discussed.

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