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1 November 2012 Stable Carbon and Nitrogen Isotope Discrimination Factors for Quantifying Spectacled Eider Nutrient Allocation to Egg Production
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Abstract

Nutrient-allocation models based on stable-isotope analysis are used to determine the nutrient sources birds invest in eggs. This approach is particularly useful for birds that migrate between habitats with distinct stable-isotope compositions. A crucial variable is the difference in stable-isotope values of egg tissues relative to diet, so appropriate adjustments can be used in models comparing nutrients from tissues to putative food sources. We established discrimination factors (Δδ) between the diet and eggs of captive Spectacled Eiders (Somateria fischeri) fed a controlled diet. Relative to diet, values of Δδ13C were higher for albumen (2.6‰), yolk protein (2.9‰), eggshell (13.0‰), and shell membrane (3.9‰), and lower for whole yolk (-1.6‰) and yolk lipid (-3.5‰). Values of Δδ15N of egg components were higher relative to diet (albumen 3.7‰, yolk protein 4.4‰, shell membrane 4.7‰, and whole yolk 3.5‰). Except for egg proteins, these patterns are generally consistent with published values for other birds. We conclude that choice of discrimination factors could markedly affect estimates of source contributions to eggs and so recommend species-specific estimates. We also provide the first reported discrimination factors between the female's diet and embryonic down feathers (Δδ13C = 2.1‰ and Δδ15N = 5.2). Finally, we determined discrimination factors between lipid and protein in diet sources and eggs, thus enabling consideration of these nutrients separately. Our study enhances the framework for nutrient-allocation modeling in eiders and likely other sea ducks.

© 2012 by The Cooper Ornithological Society. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website, http://www.ucpressjournals.com/reprintInfo.asp.
Rebekka N. Federer, Tuula E. Hollmén, Daniel Esler, and Matthew J. Wooller "Stable Carbon and Nitrogen Isotope Discrimination Factors for Quantifying Spectacled Eider Nutrient Allocation to Egg Production," The Condor 114(4), 726-732, (1 November 2012). https://doi.org/10.1525/cond.2012.110132
Received: 17 August 2011; Accepted: 11 April 2012; Published: 1 November 2012
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