Testing the usefulness of hydrogen and compound-specific stable isotope analyses in seabird feathers: a case study in two sympatric Antarctic storm-petrels
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Nitrogen and carbon stable isotopes provide tools to investigate ecological segregation, prey choice and spatial distribution in seabirds. However, the interpretation of stable isotopes is frequently hampered by a lack of isotopic baseline data. In this study, two techniques proposed to overcome such shortages were tested: compound-specific isotope analyses of amino acids (AA-CSIA) and the analysis of hydrogen stable isotope ratios (HSIA). Feathers of two sympatric storm-petrels were compared. The two species, Black-bellied storm-petrels Fregetta tropica and Wilson’s storm-petrels Oceanites oceanicus, moult in oceanic waters and differ in diet composition. For HSIA, a range of species with broad diet and non-breeding distribution was also investigated. Differences in carbon isotope values suggested differences in the spatial distribution and thus, in isotopic baseline values, during moult. Bulk nitrogen analyses of adult feathers did not detect species differences in trophic level. However, AA-CSIA detected clear differences in trophic levels in line with expectations: Black-bellied storm-petrels fed at a higher trophic level than Wilson‘s storm-petrels. Hydrogen values also differed between the species, but contrary to expectations were highly enriched in Black-bellied storm-petrels, but much less enriched in Wilson’s storm-petrels. Hydrogen data of seven petrel species challenge the suggestion that depleted δD values indicate a higher percentage of isosmotic fish. The present results suggest that the difference in hydrogen ratios may be explained by these petrels moulting in different ocean zones. Amino acid-specific stable isotope analyses were useful for estimating isotopic baselines and thus true trophic levels, whereas hydrogen isotopes were not.
We thank Vitor Paiva and two anonymous reviewers for helpful comments on the manuscript, and Joy Matthews and Chris Yarnes for running the analyses at UC Davis and discussing methodological details. We are grateful for logistic support by the Alfred Wegener Institute (Dirk Mengedoht), the Instituto Antarctico Argentino (Buenos Aires) and Department of Conservation (New Zealand).
Compliance with ethical standards
Conflict of interest
We declare that we have no conflict of interest.
This study was funded by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme SPP1154 “Antarctic Research with comparative investigations in Arctic ice areas” by a grant to PQ (Qu148/16). VN is funded by FCT, Portugal—SFRH/BPD/88914/2012.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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