Hydrogen isotope ratios in animal body protein reflect trophic level

1. Carbon and nitrogen isotope ratios in consumer tissues are known to correlate with diet isotope composition, and nitrogen isotope ratios are observed to increase with increasing trophic level. 2. We analysed nitrogen and hydrogen isotope ratios of collagen from 19 species of British fish, birds and mammals to investigate how delta D also correlated with trophic level and with feeding environment (terrestrial or aquatic). 3. A strong relationship between trophic level and delta D was discovered for both terrestrial and aquatic consumers. 4. The correlation between trophic level and delta N-15 was apparent for terrestrial consumers, but less so for aquatic consumers. 5. No differentiation was found between delta D of aquatic and terrestrial consumers at the same trophic level. 6. This observation should provide an additional tool in the study of current and ancient animal and human food web ecology.