Relationships between isotopic ratios, body condition and breeding success in a High Arctic seabird community

Predators such as seabirds are often used as bio-indicators of the marine environment.This is based on the assumption that changes in seabird populations are driven by changes in their prey.We tested this assumption in a High Arctic seabird community by assessing the relationships between the diet, body condition, and breeding performance of 4 ecologically different species: the little auk Alle alle, black-legged kittiwake Rissa tridactyla, Brünnich's guillemot Uria lomvia, and glaucous gull Larus hyperboreus, breeding in Svalbard, Norway.Interannual changes in seabird diet (2009)(2010)(2011)(2012)(2013)(2014)(2015) were assessed by estimating their carbon and nitrogen isotopic ratios (δ 15 N and δ 13 C) during the breeding and non-breeding seasons (i.e. using blood and feather tissues).We found interannual variation in the isotopic ratios during both seasons in all 4 species.These variations differed among species, thus suggesting dietary changes, instead of changes in isotopic baselines, as the most plausible mechanism underlying such patterns.We also found that seabirds had a lower average hatching success when the average δ 15 N during the previous nonbreeding season was higher.Our results suggest that changes in the average prey composition during the non-breeding season may partially explain changes in breeding performance of Svalbard seabirds.