Quantifying diet to tissue isotopic (δ¹³C and δ¹⁵N) fractionation factors in captive spectacled eiders (Somateria fischeri): implications for nutrient allocation and foraging studies

Abstract

"The spectacled eider (Somateria fischeri) was listed as threatened under the Endangered Species Act in 1993, and potential threats to population recovery include changes in the marine prey abundance and availability. Therefore, development of diet assessment techniques has been listed as an eider recovery task. Stable isotopes have been used to evaluate foraging ecology and nutrient allocation to reproduction in birds. Application of this technique requires knowledge of how stable isotope signatures of animal tissues differ from their diet, referred to as isotopic fractionation, and these values can be determined experimentally using captive populations. I established stable isotopic fractionation factors for d¹³C and d¹⁵N from diet to egg components, down feathers, contour feathers, cellular blood, blood plasma, and fat of captive spectacled eiders. Sensitivity analyses indicate that choice of isotopic fractionation values from eggs of different species could considerably alter model conclusions. Therefore, I incorporated isotopic fractionation factors from spectacled eider eggs into two published sea duck nutrient allocation models that previously used these values from falcons (Falco spp.) to assess differences in model conclusions. Results from these studies provide further resources to understand foraging and nutrient transfer in eiders and may offer more accurate estimates for sea duck models"--Leaf iii