Differences in stable isotopes in blood and feathers of seabirds are consistent across species, age and latitude: implications for food web studies
Stable isotopes of growing feathers and blood both represent assimilated diet, and both tissues are used to study the diet and foraging distribution of marine and terrestrial birds. Although most studies have assumed that both tissues represent a difference of one trophic level to diet, the enrichment factors of blood and feathers may differ, especially where endogenous reserves are used as precursors during feather synthesis. In this study, we compare carbon and nitrogen stable isotopes of blood and simultaneously growing feathers of five species of Procellariiformes, representing five genera, different geographical regions and different life stages (chicks and adults). In all species, feathers were enriched in 15N and 13C compared with blood. Isotopic values of carbon and nitrogen were correlated in different tissues growing simultaneously for most species analyzed, suggesting that mathematical corrections could be used to compare different tissues. Our results imply that more care needs to be taken when comparing stable isotope signatures across studies assuming different tissues are equivalent indicators of trophic ecology.
KeywordsUric Acid Stable Isotope Nitrogen Stable Isotope Nitrogen Isotope Ratio Isotope Turnover
We are grateful to the following organizations that facilitated fieldwork: New Island Conservation Trust, Projeto Albatroz, captain and crew of fishing vessel ‘Ana Amaral’ and the Brazilian Navy. NERC funded the isotope analysis. We would like to acknowledge financial support by DFG, Germany (Qu 148/1-ff), and New Island Conservation Trust. Fieldwork at New Island was approved by the Falkland Islands Government (Environmental Planning Office) and in Brazil by environmental agency (IBAMA) through permits No. 0128931BR, No. 203/2006, No. 02001.005981/2005, No. 023/2006, No. 040/2006 and No. 1282/1, and International Animal Health Certificate No. 0975–06. The Scottish Executive-Rural Affairs Directorate also kindly provided us the permit POAO 2007/91 to import samples into Scotland. LB received a CAPES Scholarship.
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