The habitat niche breadth in a zooplanktivorous High Arctic seabird as an indicator of ocean-related pressures

AbstractSeabirds adjust their foraging behaviour to cope with changing environmental conditions by changing prey choice, foraging locations and trip characteristics. We studied the foraging ecology of zooplanktivorous little auks (Alle alle) during chick-rearing in SW Spitsbergen across seven years (2011–2024), using GPS tracking, oceanographic data and diet analyses. Across years, little auks consistently foraged within the same core and home ranges over the continental shelf and its break, within a 150-km buffer around the colony. However, within this range, they demonstrated plasticity by adjusting their foraging strategies in response to environmental conditions. Birds adopted a consistent foraging strategy under optimal conditions and shifted to a flexible strategy when conditions became suboptimal, primarily by changing local foraging sites. These shifts resulted in interannual variation in habitat niche size: under favourable conditions (low sea surface temperature and intermediate chlorophyll-a), birds utilized a narrow niche, whereas in warmer, high-productivity years, they broadened it. Despite environmental variability, diet remained dominated by cold-water copepods (Calanus glacialis, 74.6%–89.7%). In suboptimal years, as in warm 2023, they supplemented chick diets with 16% furcilia larvae of Euphausiacea sp. Our results suggest that, in seabirds, habitat niche breadth is a valuable indicator of ocean-related conditions.