Feeding ecology analysis supports a marine diet in the extinct Chatham Island Duck (Anas chathamica)

ABSTRACT

The Chatham Island Duck, Anas chathamica, is one of many New Zealand bird species that became extinct after Polynesian arrival. The Chatham Island Duck was a large flightless bird, with salt glands on its skull, which led to the hypothesis that it lived in a marine habitat. We tested this hypothesis using a combination of stable isotope analysis (carbon and nitrogen) and analysis of morphoanatomical features. We also conducted a comparative analysis with other anatids from the Chatham Islands and New Zealand. Furthermore, we trialled the non-destructive technique of portable X-ray fluorescence (elemental composition of bones) to assess whether it can be helpful for reconstructing the ecology and habitat of extinct species. We obtained data from museum specimens: 12 samples of A. chathamica and 55 of other anatids for isotope analysis; and 23 samples of A. chathamica and 63 of other anatids for X-ray fluorescence. Results from isotope analysis, supported by anatomical features, show that A. chathamica had a more fully marine diet than previously hypothesised, mainly composed of invertebrates. The large body size of A. chathamica is possibly related to territoriality and combat, which is also supported by the presence of carpal weaponry. Our data demonstrate the importance that the marine environment likely played in the life of this extinct species, while highlighting the key role natural history collections can have in ecological studies.

KEYWORDS:

• Anas chathamica
• Anatidae
• New Zealand
• stable isotopes
• X-ray fluorescence

Acknowledgements

The isotope data set used here stems from a joint project of Murray J. Williams and Richard N. Holdaway that took place in 2000–2005; we are very grateful to them for inspiring us to take on this project and the discussions and encouragement along the way. We are likewise grateful to the two anonymous reviewers and the associate editor Kate Buchanan, whose comments and suggestions helped to improve this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).