Stable carbon and nitrogen isotope discrimination factors from diet to blood plasma, cellular blood, feathers, and adipose tissue fatty acids in Spectacled Eiders (Somateria fischeri)

Abstract

Stable isotope analyses of animal tissues can be used to infer diet through application of mixing models. An important component in a mixing model is the incorporation of stable isotope discrimination factors so that isotopic shifts between diet and tissues built from the diet can be accounted for when comparing tissues to potential food sources. We determined the stable carbon and nitrogen isotopic discrimination factors between lipid-free diet and blood plasma, cellular blood, and adult chest contour feathers for captive female Spectacled Eiders ( Somateria fischeri (Brandt, 1847)). Mean discrimination factors for blood components and feathers were either similar or slightly larger compared with previously studied species. Additionally, we determined the stable carbon isotope discrimination factors between dietary lipids and adipose tissue fatty acids using three adipose tissue biopsies from captive male Spectacled Eiders that were fed three different diet treatments. Isotopic signatures of adipose tissue fatty acids closely reflected shifts in the diet and were either similar to or increased relative to diet. Our study provides a foundation for research using tissues as end-members in stable isotope nutrient allocation models and foraging ecology studies of Spectacled Eiders, and will provide the most applicable isotope data to date for sea ducks.

Discrimination Factors for Stable Isotopes of Carbon and Nitrogen in Blood and Feathers from Chicks and Juveniles of the California Condor

“…The mean Δ 13 C (0.9‰) and Δ 15 N (3.3‰) values from plasma collected from juvenile condors were slightly higher (C) or lower (N) than the range of values for plasma reported in other studies in which the birds were held on all animal protein (0 to 0.5‰ for C and 4.9‰ for N;Clark 1993, Federer et al 2010) (Table 3). The mean Δ 13 C (0.3‰) and Δ 15 N (1.8‰) values from RbCs from the fully grown juvenile condors we studied were well below the range observed in other carnivorous birds (2.0 for C, 4.0 for N; Federer et al 2010) (Table 3), and the mean Δ 13 C and Δ 15 N values from whole blood from chicks (1.7‰ and -0.7‰, respectively) and juvenile condors (1.9‰ and 0.3‰, respectively) were within the range observed in other birds (1.1-7.1‰ for C, 1. 9-4.2‰ for N;Clark 1992b, bearhop et al 2002) (Table 3).…”

“…As we found in the condor, the Δ 15 N values from plasma are higher than those from RbCs and whole blood of Dunlins (Calidris alpina) (Evans Ogden et al 2004) held on a mixed wheat/ animal protein diet, whole blood of yellow-rumped Warblers (Setophaga coronata) held on a mixed banana/insect or 100% insect diet (Pearson et al 2003), and RbCs of Spectacled Eiders (Somateria fischeri) (Federer et al 2010) held on a Whole blood 1.7 to 1.8 -1.2 to 1.8 Pearson et al (2003) commercial duck diet mixed with fish (Table 3). The Δ 13 C values from plasma were lower than those from whole blood for the warblers (Pearson et al 2003), whole blood from American Crows held on an all-fish diet Clark 1992b, 1993), and RbCs from the Spectacled Eider (Federer et al 2010) and Dunlin (Evans Ogden et al 2004) (Table 3). These variations in the patterns of Δ 13 C and Δ 15 N values observed among blood components of various species further underscore the need for studies determining stable-isotope discrimination factors across multiple tissues.…”

“…These variations in the patterns of Δ 13 C and Δ 15 N values observed among blood components of various species further underscore the need for studies determining stable-isotope discrimination factors across multiple tissues. 1992b, bearhop et al 2002, Federer et al 2010, but the mean Δ 13 C values (0.4‰) for these feathers were well below those from other birds (1.4 to 7.0‰;hobson and Clark 1992b, bearhop et al 2002, Federer et al 2010 (Table 3). We do not know the cause of the difference between our values and other published Δ 13 C values from feathers, but our feathers were from growing chicks and the feathers in other studies were from adults.…”

Carbon isotopic fractionation in eider adipose tissue varies with fatty acid structure: implications for trophic studies

“…New techniques using minimally invasive sampling methods and biochemical signatures in stored fat Wang et al, 2010), blood (Käkelä et al, 2009;Federer et al, 2010), stomach oil (Connan et al, 2005;Wang et al, 2007), feathers (Hobson and Clark, 1992) or eggs (Hobson, 1995;DeVink et al, 2011) provide promising alternatives for diet assessments in avian populations. These biomarker techniques typically involve either stable isotope or fatty acid (FA) analysis.…”

“…However, there are limitations to the bulk isotope (i.e. measurement of the isotopic composition of total organic carbon or nitrogen in a sample) approaches, including isotopic routing and fractionations from diet to tissue that can complicate interpretation (Federer et al, 2010). As an alternative, FA signature analysis has been used to investigate diets of higher predators (e.g.…”