Breeding Biology of Least Auklets on the Pribilof Islands, Alaska

Abstract

Aspects of Least Auklet (Aethia pusilla) breeding biology that pertain to the growth and development of chicks were studied on St. George Island, Bering Sea, Alaska, during the 1981 and 1982 breeding seasons. Yolk was 41% of fresh egg contents, a greater value than in the eggs of other alcid species. Adult incubation shifts averaged 24 hr, and both parents frequently spent the night together in the nest during both the incubation and chick-rearing periods. Adults brooded nestlings continuously during the day until 6 days post-hatching; diurnal brooding then declined gradually until cessation by Day 18. Chicks grew rapidly and achieved peak mass by 20 days posthatching; most fledged at masses greater than average adult body mass. Nestlings were fed an average of 5.3 meals day-1; meals averaged 5.4 g and consisted mostly of Neocalanus copepods. Estimates of breeding success (72% and 66% in 1981 and 1982, respectively) were about average for alcid species. The short nestling period of Least Auklet chicks is associated with frequent meal delivery and extended brooding made possible by the diurnal, nearshore foraging behavior of parents. Diurnal activity and nearshore foraging during the breeding season appear to be adaptations that minimize the duration of nesting and the associated risk of fox predation.