MEPS 739:241-256 (2024)  -  DOI: https://doi.org/10.3354/meps14614

ABSTRACT: Little is known about the spatial and dietary overlap of seabird species during the non-breeding season, when scarce and patchy marine food resources could lead to interspecific competition. We aimed to quantify spatiotemporal and isotopic niche overlap among common murres Uria aalge, razorbills Alca torda, and Atlantic puffins Fratercula arctica outside the breeding season by combining data from geolocators and stable isotope ratios (δ¹⁵N, δ¹³C) of belly, secondary, and head feathers collected in 2017-2020 from birds breeding in coastal northeastern Newfoundland, Canada. Seasonal utilization distributions of each species indicated generally low spatial overlap during most of the non-breeding period, with exceptions immediately post-breeding and with variability in movement paths among puffins. Stable isotope analysis revealed a broader isotopic niche (1.5 to 3×) for puffins than other species, matching their greater spatial variation. There was no isotopic niche overlap among the 3 species, except during flight feather molt of razorbills and murres. Individual puffins located in the same area as razorbills or murres had lower δ¹⁵N values, suggesting a lower trophic position. The minimal overlap of these 3 alcid species during an understudied phase of their annual cycle suggests that they segregate spatially and partition resources, implying that different spatial planning and ecosystem conservation strategies should be applied to each of these 3 species.

KEY WORDS: Seabird · Interspecific competition · Distribution · Stable isotope · Geolocator · North Atlantic · Alcid