Foraging strategy of the little auk Alle alle throughout breeding season - switch from unimodal to bimodal pattern

Energy and time allocation differs between incubation and chick-rearing periods, which may lead to an adjustment in the foraging behaviour of parent birds. Here, we investigated the foraging behaviour of a small alcid, the little auk Alle alle during incubation and compared it with the chick-rearing period in West Spitsbergen, using the miniature GPS (in Hornsund) and temperature loggers (in Magdalenefjorden). GPS-tracking of 11 individuals revealed that during incubation little auks foraged 8-55 (median 46) km from the colony covering 19-239 (median 120) km during one foraging trip. Distance from the colony to foraging areas was similar during incubation and chick-rearing period. During incubation 89% of foraging positions were located in the zone over shallower parts of the shelf (isobaths up to 200-300 m) with sea surface temperature below 2.5 degrees C. Those environmental conditions are preferred by Arctic zooplankton community. Thus, little auks in the Hornsund area restrict their foraging (both during the incubation and chick-rearing period) to the area under influence of cold, Arctic-origin water masses where its most preferred prey, copepod Calanus glacialis is most abundant. The temperature logger data (from 4 individuals) indicate that in contrast to the chick-rearing period, when parent birds alternated short and long trips, during the incubation they performed only long trips. Adopting such a flexible foraging strategy allows little auks to alter their foraging strategy to meet different energy and time demands during the two main stages of the breeding.