Stable isotopes and fatty acid signatures reveal age- And stage-dependent foraging niches in tufted puffins

Major breeding failures of seabird populations are sometimes attributed to reduced egg laying or abandonment of incubation due to nutritional stress, yet diets during these reproductive stages are often poorly characterized. We used stable isotopes and fatty acid (FA) signatures to infer age- (adult vs. nestling) and stage-dependent foraging niches of tufted puffins Fratercula cirrhata captured in Chiniak Bay, Kodiak Island, Alaska, USA, from 2003 to 2005. Whole blood δ¹⁵N values indicated a seasonal shift in trophic niche of adults: ¹⁵N enrichment was consistent with a 0.47 to 0.68 increase in trophic level of feeding from pre-lay to late chick-rearing. Although incomplete turnover of blood cells from the pre-lay period likely contributed to intermediate δ¹⁵N values of incubating puffins, this was insufficient to account for differences between incubating and chick-rearing adults. Differences in δ¹⁵N and δ¹³C between chick-rearing adults and nestlings were small and inconsistent between years. Discriminant function analysis (DFA) using the 14 most abundant FAs classified individuals by reproductive stage and age within each year with a high level of accuracy (linear DFA: 93 to 99%; quadratic DFA: 80 to 92%). When all years were combined, accuracy of cross-validated classification remained high (linear DFA: 90%; quadratic DFA: 76%). Based on stable isotopes and FA signatures, we conclude that foraging niches are stage-dependent in this species and suggest that chick-rearing adults do not typically feed at a lower trophic level than nestlings but likely consume a different array of prey species.