Using stable isotopes to determine seabird trophic relationships

1. The stable isotopes of nitrogen (δ¹⁵N) and carbon (δ¹³C) were analysed in 22 species of marine birds from coastal waters of the northeast Pacific Ocean. Analyses confirm that stable nitrogen isotopes can predict seabird trophic positions.

2. Based on δ¹⁵N analyses, seabird trophic-level inferences generally agree with those of conventional dietary studies, but suggest that lower trophic-level organisms are more important to several seabirds than was recognized previously.

3. Stable-carbon isotope analysis may be a good indicator of inshore vs. offshore feeding preference.

4. In general, stable-isotope analysis to determine trophic level offers many advantages over conventional dietary approaches since trophic inferences are based on time-integrated estimates of assimilated and not just ingested foods, and isotopic abundance represents a continuous variable that is amenable to statistical analysis.