Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

Abstract

The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration.

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

“…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 include taxon, type of tissue analyzed, differences in digestive physiology, nutritional or reproductive status, form of waste, macromolecular composition of the diet (i.e., proportions of protein, carbohydrate, and lipid), as well as the extent of routing of dietary macromolecules to the same macromolecules in body tissues (i.e., dietary protein to body protein or dietary fat to body fat) (bearhop et al 2002, kurle 2002, McCutchan et al 2003, Pearson et al 2003, Vande rklift and Ponsard 2003, Robbins et al 2005, Martínez del Rio et al 2009, lecomte et al 2011, Poupin et al 2011. given the propensity for variation, the use of assumed discrimination factors in stable-isotope mixing models can result in significant errors in the estimation of wild animals' foraging ecology (bond andDiamond 2011, Phillips 2012;kurle, unpubl.…”

Pleistocene to recent dietary shifts in California condors

“…However, controlled isotopic studies of diet and bird tissues show that these isotopic fractionations can vary significantly among tissue types and bird species (9,27,28). Although there are no controlled feeding studies of condors, recent work suggests that, as the protein content of diet rises, the diet-to-tissue fractionation increases for both carbon and nitrogen (28,29). Trophic 15 N enrichments of 4‰ are common for birds on high-protein diets (27)(28)(29).…”

“…Although there are no controlled feeding studies of condors, recent work suggests that, as the protein content of diet rises, the diet-to-tissue fractionation increases for both carbon and nitrogen (28,29). Trophic 15 N enrichments of 4‰ are common for birds on high-protein diets (27)(28)(29). Some of these studies also show diet-to-keratin 13 C enrichments of Ն3‰ for birds on high protein diets (27,29).…”

“…Trophic 15 N enrichments of 4‰ are common for birds on high-protein diets (27)(28)(29). Some of these studies also show diet-to-keratin 13 C enrichments of Ն3‰ for birds on high protein diets (27,29). In many cases, however, these diets contain substantial amounts of lipid, which is 13 C depleted relative to bulk diet and dietary protein.…”