Time allocation and foraging behaviour of chick-rearing Brunnich's Guillemots Uria lomvia in high-arctic Greenland

Data-loggers were used to measure the flight and diving activity of Brunnich's Guillemots Uria lomvia breeding in a colony in the North Water polynya. During a total of 51.1 bird-days the birds spent an average of 16.6% (4.0 h/day) of their time underwater, 7.1% in flight (1.7 h/day), 25.4% surface swimming and 50.9% on nest attendance. At-sea time budget included time spent commuting through the water column (8.0% of total time), bottom time available for chasing prey (8.6%), interdive breaks on the surface (9.9%) and long breaks between diving bouts (15.6%). Mean dive duration was 122.9 (+/- 45.4 sd) s (maximum 240 s). Median dive depth was 48.9 m, but birds showed highly individual depth preferences. Mean foraging trip duration was 8.9 +/- 1.3 h, but differed significantly between individuals (range 1.37-20.4 h). The number of dives performed during a trip increased with trip duration, as did total time spent flying, suggesting long trips were used to reach distant foraging grounds and the whole trip was used for active foraging. The birds spent an average of 1.3 +/- 0.8 h/day in flight, and estimated potential foraging range averages 42 +/- 25.9 km; 67% of all trips could not have exceeded 50 km. Trip start and dive initiation were bimodally distributed with peaks morning and evening despite continuous daylight in the study area. Compared to studies of time allocation and trip duration in Common Guillemot populations, the high-arctic Brunnich's Guillemots seemed to work harder during the breeding season, and to have few options for further increasing foraging effort.