Habitat selection of foraging chick-rearing European shags in contrasting marine environments

Impacts of anthropogenic activities on coastal seabirds might be extensive, especially in the breeding season. Identifying important foraging areas and associated habitats is important for a proper management of seabirds. To identify habitat characteristics driving the selection of foraging sites of breeding European shags Phalacrocorax aristotelis, this study used tracking data (GPS- and TDR-loggers), from 282 individual birds comprising 905 foraging trips and 27,303 dives with known locations, to create habitat selection models. To explore possible effects of regional differences in habitat on foraging behavior, the study was performed at two Norwegian colonies, Sklinna in the Norwegian Sea (65°N, 11°E) and Hornøya in the Barents Sea (70°N, 31°E), with distinct differences in seascape structure and habitat availability. Shags at Sklinna foraged further away from the colony than those at Hornøya but diving depth and duration were similar at the two colonies. In both colonies, sea depth was an important predictor of habitats selected by chick-rearing shags during foraging, with birds preferring shallow depths. At Sklinna, shags also selected for flat areas with high probability of kelp forest occurrence. There was no difference in trip length and duration between sexes, but males dived deeper than females in both colonies. This suggests that males and females might utilize different microhabitats within the same foraging area. The study discusses the application of habitat selection modeling to identify important foraging areas for coastal seabirds, and how this may contribute to the management, conservation and assessment of impacts of human activities.