Inter- and intra-annual differences in foraging ecology of the chick-rearing Brünnich's guillemots (Uria lomvia) breeding in the High Arctic.

The foraging ecology of seabirds depends on both external and internal factors. Seabirds can modify their feeding strategy depending on current food availability to maintain optimal energy levels provisioned to the offspring. Here, we investigated inter- and intra-annual variability of the foraging ecology of the Brünnich's guillemot (Uria lomvia) breeding in a High Arctic colony on Spitsbergen (Svalbard) combining GPS tracking and remote sensing. Despite different environmental conditions in the studied years, covered distances and duration of foraging trips were similar. The studied individuals generally foraged in cold waters at shelf and shelf break zones located up to 100 km from the colony (median 51 km). They foraged at colder waters with lower primary productivity in colder 2015 compared with warmer 2016 but still used areas of similar depth. They explored a narrower foraging habitat niche (described by sea surface temperature, chlorophyll a concentration, sea depth and seabed slope in foraging locations) in warmer 2016, suggesting a lower variety of microhabitats where the preferred prey was available. With progress of the chick-rearing period, they foraged further from the colony, suggesting temporal prey depletion halo effect. Our findings provide valuable insight into spatio-temporal variability of seabird foraging ecology in the rapidly changing High Arctic.