Multidimensional niche differentiation of chick-rearing sympatric auks in the Gulf of St. Lawrence

Niche theory predicts that similar species cannot occupy the same geographical space when resources are limited. Sympatric seabirds, such as auks, are ideal models for investigating niche differentiation because they share life history traits and form breeding colonies that rely on common prey items. Auk differentiation may be driven by variations in body mass and wing size, diving capacity, and visual acuity leading each species to forage at different distances, depths, or times of day, respectively. However, previous auk studies have produced diverse results, leaving us with an incomplete understanding of their foraging differentiation across spatial, environmental, and temporal dimensions. In 2021, we tested niche differences at the Mingan Archipelago National Park Reserve, Québec, Canada (50°11′ N, 63°13′ W) by utilizing GPS and time and depth recorders to track the positions of breeding Atlantic puffins (Fratercula arctica), razorbills (Alca torda), and common murres (Uria aalge), which were then paired with environmental data. There was high niche overlap in geographical foraging areas, with auk wing size and mass not appearing to influence their foraging distance. Instead, auk foraging was partitioned over different depths and times of day. Although razorbills and puffins generally exploited shallow foraging areas, puffin foraging activity occurred in deeper waters and at different times of day than razorbills. Murres foraged in the deepest benthic areas and were the only species to forage at night. Our study therefore suggests that auks could be facilitating their coexistence by exhibiting temporal and spatial differences in their foraging behaviours and locations.