Seabird species‐ and assemblage‐level isotopic niche shifts associated with changing prey availability during breeding in coastal Newfoundland

• Published in: Ibis
• Main Authors: Jenkins, Edward J., Davoren, Gail K.
• Other Authors: University of Manitoba, World Wildlife Fund
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Alca torda; Atlantic puffin; Common Murre; fratercula; Fratercula arctica; Newfoundland; Oceanodroma leucorhoa; Razorbill; Uria aalge; uria
• Online Access: http://dx.doi.org/10.1111/ibi.12873; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fibi.12873; https://onlinelibrary.wiley.com/doi/pdf/10.1111/ibi.12873; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/ibi.12873

Shifting prey availability can lead to altered species interactions, indicated by variation in the dietary niche breadth and position of species within an assemblage. On the Newfoundland coast, annual inshore spawning migration of the dominant forage fish, Capelin Mallotus villosus , provides an excellent opportunity to investigate the influence of varying prey availability on dietary niche breadth and position among species. During June–August 2017, we investigated species‐ and assemblage‐level dietary responses to shifting Capelin availability of three Capelin‐eating, sympatrically breeding auk species, the Atlantic Puffin Fratercula arctica , Razorbill Alca torda and Common Murre Uria aalge . The diet of Leach's Storm Petrels Oceanodroma leucorhoa , which breed alongside the three auk species but are not known to rely on Capelin, was also examined to determine dietary shifts throughout breeding that were unrelated to Capelin availability. We quantified stable isotope ratios (δ 15 N, δ 13 C) in seabird blood components (plasma, cellular component) collected both before and after spawning Capelin arrived in the study area and compared isotopic niche breadth within a Bayesian framework. At the species level, auk trophic position increased and isotopic niche breadth narrowed after Capelin arrived, suggesting a more Capelin‐based diet. Simultaneously, trophic diversity of the auk assemblage, reflecting the extent of spacing among niches of species, decreased after spawning Capelin arrived inshore. Contrastingly, increased trophic position but broader isotopic niche breadth during higher relative to lower Capelin availability for Leach's Storm Petrel confirm that this species is probably not affected by the inshore arrival of Capelin, but instead that isotopic changes may be more related to a shift in breeding stage to chick‐rearing. Overall, our findings reiterate the importance of Capelin as a prey resource for breeding auks in coastal Newfoundland, but that the degree of reliance on Capelin varies among species, ...