The annual cycle of Northern Fulmars (Fulmarus glacialis) in the western Gulf of Alaska includes about six months from mid-April to mid-October when birds are associated with land at the Semidi Islands. The pre-laying stage in five years was marked by recurrent peaks in attendance that included up to 90% of the population, and alternate periods of 2 to 12 days when the breeding ground was deserted. Serial correlation of daily attendance indicated a cyclic pattern with a half-period of five to seven days. Maximum attendance at breeding sites usually occurred in the evening after a gradual increase in numbers during the day. Percentage of attendance by nonbreeding and failed birds varied widely with breeding success, but the seasonal occurrence of nonbreeders followed a consistent pattern: attendance by siteholding nonbreeders peaked before egg-laying, then steadily declined, whereas an influx of nonbreeding floaters occurred in July and August. Different wind directions and speeds influenced the number of birds at the colony for up to three days after they occurred, but it was not possible to explain the birds' behaviour during the pre-laying period in terms of simple linear relationships between attendance and weather. Rather, synchronized attendance appeared to be a social phenomenon mediated by environmental cues such as a change in wind direction.
