Breeding seasons of oceanic birds in a subarctic colony

Abstract

On the Semidi Islands, W Gulf of Alaska, distributions of laying or hatching observed in 11 species during 1-7 yr are presented; less detailed information is available on the breeding schedules of 3 species. The combined laying period of 14 species lasted 3 months from mid-April to mid-July; the 1st eggs of the earliest and latest species were laid c9 wk apart. Mean laying dates varied by 2-16 days in 9 species. Although the egg-laying sequence of species was largely preserved from year to year, there was little evidence of concordant annual variation in breeding seasons. Species that fed lower in the food chain tended to breed earlier than those that fed at higher trophic levels. Early laying was correlated with longer laying periods, both within and between species. With the exception of 3 puffin species, birds with similar food habits exhibited less overlap in hatching and fledging dates than laying dates. There was no evidence for competitive avoidance of breeding overlap in piscivores or planktivores. Species may not have timed their egg laying to provide for maximum food availability during chick rearing. Breeding times were probably determined more by the food requirements of laying females. Young females laying relatively late probably account for the right-skewed distributions of egg laying observed in this and other studies of colonial seabirds. -from Authors