Can variations in the spatial distribution at sea and isotopic niche width be associated with consistency in the isotopic niche of a pelagic seabird species?

Abstract

This study tested for fluctuations on short-term consistency (within about 1 month) in the isotopic niche of a pelagic seabird species. Short-term consistency in the isotopic niche was assessed using a wide-ranging apex predator, the Cory's shearwaters Calonectris diomedea, along a 3-year study (2010-2012), during both the pre-laying and chick-rearing periods, with markedly inter- and intra-annual differences in the foraging spatial distribution at sea and isotopic niche width. We used individual movement data and stable isotope data, analysed using recent metrics based in a Bayesian framework, of 69 adults breeding on a small neritic island in the North Atlantic (39A degrees 24'N, 009A degrees 30'W). As expected, our results confirm that isotopic niche expansion could arise via increased variation in spatial distribution at sea among individuals. Results suggest fluctuations on short-term consistency in the isotopic niche of Cory's shearwaters related to their different foraging patterns among periods and, ultimately, to presumably temporal changes in the availability and predictability of food resources. Short-term consistency in the isotopic niche was higher and persistent during periods when the population showed an intermediate isotopic niche width and absent when isotopic niche was either smaller or larger during the study period. These results suggest that consistency in the isotopic niche is an important characteristic of this population during the breeding period that may fluctuate depending on resources availability and should be important to understand the dynamics of foraging ecology of pelagic seabirds in general.