USING STABLE ISOTOPES TO DETERMINE SEABIRD TROPHIC RELATIONSHIPS

1. The stable isotopes of nitrogen (deltaN-15) and carbon (deltaC-13) were analysed in 22 species of marine birds from coastal waters of the northeast Pacific Ocean. Analyses confirm that stable nitrogen isotop es can predict seabird trophic positions. 2. Based on deltaN-15 analys es, seabird trophic-level inferences generally agree with those of con ventional dietary studies, but suggest that lower trophic-level organi sms are more important to several seabirds than was recognized previou sly. 3. Stable-carbon isotope analysis may be a good indicator of insh ore vs. offshore feeding preference. 4. In general, stable-isotope ana lysis to determine trophic level offers many advantages over conventio nal dietary approaches since trophic inferences are based on time-inte grated estimates of assimilated and not just ingested foods, and isoto pic abundance represents a continuous variable that is amenable to sta tistical analysis.