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Stable hydrogen isotope measurements of songbird feathers: effects of intra-feather variability and sample processing

  • Oscar GordoEmail author
Original Article

Abstract

Deuterium composition of feathers has been widely applied to establish provenance of birds. Surprisingly, little attention has been paid to the potential sources of unwanted hydrogen isotopic variability that may affect the comparability and replicability of deuterium measurements. Feathers may exhibit hydrogen isotopic differences between distal and proximal sections, as well as between rachis and vane. For this reason, it is recommended to always analyse ground vane from the same section of the feather. However, this protocol may be seriously limiting when working with songbird feathers, which are usually small and light. In this paper, intra-feather hydrogen isotopic variability was studied in four species of songbirds by comparing four sections of the same feather. No difference in hydrogen isotopic composition was found between distal and proximal sections of the vane. This was expected as songbird feathers grow rapidly and individuals avoid geographical movements during moult, favouring a homogeneous source of hydrogen during keratin synthesis. Conversely, as previously demonstrated for other avian species, rachis showed systematically c. 11‰ δ2H more negative values than vane. This is probably a result of their biochemical and ultrastructural differences, which seem strongly conserved across taxa. Such differences imply that we need to describe which feather part was used in the methods of our reports to ensure full comparability and replicability among studies. Nevertheless, vane and rachis δ2H were strongly correlated, demonstrating that rachis can be also used in isotope analyses because its δ2H can be accurately rescaled. This is useful since rachis represents an important fraction of feather mass in songbirds. Values of δ2H from ground and non-ground samples from the same feather were also compared. There was no effect of the processing protocol, suggesting that grinding is unnecessary when working with passerine feathers.

Keywords

Deuterium Keratinous material Methodology Passerines Protocol Tissue 

Zusammenfassung

Messungen stabiler Wasserstoffisotopen in Singvogel-Federn: Effekte der Intra-Federn-Variabilität und Probenverarbeitung

Die Deuteriumzusammensetzung von Federn wird üblicherweise eingesetzt, um die Herkunft von Vögeln festzustellen. Überraschenderweise wird dabei aber nur wenig auf potenzielle Quellen einer unerwünschten Wasserstoffisotopen-Variabilität geachtet, die die Vergleichbarkeit und Wiederholbarkeit der Deuteriummessungen beeinflussen können. Federn können zwischen ihren distalen und proximalen Abschnitten sowie zwischen Wirbelsäule und Flügeln Unterschiede in den Wasserstoffisotopen aufzeigen. Deshalb empfiehlt es sich, Analysen stets von den gleichen Federabschnitten zu machen. Diese Regel führt jedoch bei Singvogelfedern zu einer ernsthaften Einschränkung, weil diese normalerweise klein und leicht sind. In dieser Studie untersuchten wir bei vier Singvogelarten die Wasserstoffisotopen-Variabilität in den gleichen Federn, indem vier Abschnitte derselben Feder verglichen wurden. Zwischen dem distalen und proximalen Abschnitt desselben Flügels wurden keine Unterschiede in der Wasserstoffisotopen-Zusammensetzung gefunden. Das war erwartet worden, weil Singvogelfedern schnell wachsen und die einzelnen Tiere Ortsveränderungen während der Mauser vermeiden und somit während der Keratin-Synthese eine homogene Wasserstoffversorgung haben. Andererseits, wie schon früher für andere Vogelarten festgestellt, zeigt der Schaft systematisch ca. 11‰ δ2H mehr negative Werte als die Federfahne. Vermutlich liegt das an biochemischen und ultrastrukturellen Unterschieden, die sich durch alle Taxa hindurchziehen. Diese Unterschiede machen es empfehlenswert, immer anzugeben, welche Federabschnitte verwendet wurden, um eine volle Vergleichbarkeit und Wiederholbarkeit der Untersuchungen zu gewährleisten. Nichtsdestotrotz korrelierten die δ2H von Schaft und Fahne hoch miteinander und zeigten, dass auch der Schaft für die Isotopenanalyse benutzt werden kann, weil seine δ2H-Werte entsprechend korrekt skaliert werden können. Das ist deshalb sehr hilfreich, weil bei Singvögeln der Schaft einen wichtigen Anteil der gesamten Federmasse darstellt. Die δ2H-Werte von zermahlenen und nicht zerkleinerten Proben der gleichen Federn wurden ebenfalls untersucht und kein Unterschied festgestellt, was nahelegt, dass bei der Arbeit mit Singvogelfedern ein Zermahlen der Federn unnötig ist.

Notes

Acknowledgements

I thank to José Luis Arroyo, Rubén Rodríguez, Ángel Sallent and Benito Fuertes for collecting samples, and Sarai López and Manuela G. Forero for their assistance in the lab. I am especially grateful to Margarida Barceló-Serra for her manuscript review and English edits. Two anonymous reviewers provided helpful comments that improved a first version of this article. Feather sampling was conducted in accordance with Spanish law, approved by the Ethical Committee of the CSIC (Ref. 23/02/2018/015), and with the permits given by the Dirección General de Gestión del Medio Natural y Espacios Protegidos de la Junta de Andalucía, and the Espacio Natural de Doñana (No. 2017/20). OG also has a training certificate (No. 000023) given by the IFAPA (Junta de Andalucía) which, according to Spanish Law (ECC/566/2015), is necessary for any experiments with animals. This study was funded by a grant to OG from the Spanish Ministry of Economy (Ref. CGL2014-56041-JIN).

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Copyright information

© Deutsche Ornithologen-Gesellschaft e.V. 2019

Authors and Affiliations

  1. 1.Department of Conservation BiologyDoñana Biological Station (EBD-CSIC)SevilleSpain

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