Patterns of colony attendance in the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Abstract

The annual cycle of colony attendance of the Cape Petrel Daption capense at Nelson Island, Antarctica, covered about 9 months from the start of September until the end of May. Large numbers of birds attended the colony continuously for 6 months from arrival until fledging, except for a 2‐week incomplete pre‐laying exodus when attendance was reduced to 10% of that during incubation. After 1 month (March) of post‐fledging absence, birds returned to the colony for 2 months in numbers comparable to the level in the breeding season. This was followed by a winter absence that lasted only 3 months and was interrupted by two short visits by a small number of birds. Mean attendance was highest during incubation, but short peaks of maximum attendance occurred during the pre‐breeding period. Except for the incubation and brooding periods, colony attendance showed high variability both within and between days. Large numbers of visiting birds occurred on the sea and on islets in front of the colony until the end of October. Unemployed birds constituted an almost constant proportion of up to 50% of colony‐attending birds during the incubation period. Diurnal variability did not show a consistent pattern but may represent preferential feeding during early morning hours, with additional short departures depending on the length of the daylight period. Colony counts were the most consistent during the second half of incubation, when the lowest counts gave an estimate of the number of breeding pairs and peak numbers an impression of the additional number of attending nonbreeders. Pre‐breeding counts revealed the maximum numbers of birds associated with a particular colony. However, for both pre‐ and post‐breeding surveys, several counts a day over a period of at least a week are recommended because of variability in attendance.