Effects of nutritional restriction on nitrogen and carbon stable isotopes in growing seabirds

Abstract

When using stable isotopes as dietary tracers it is essential to consider effects of nutritional state on isotopic fractionation. While starvation is known to induce enrichment of (15)N in body tissues, effects of moderate food restriction on isotope signatures have rarely been tested. We conducted two experiments to investigate effects of a 50-55% reduction in food intake on delta(15)N and delta(13)C values in blood cells and whole blood of tufted puffin chicks, a species that exhibits a variety of adaptive responses to nutritional deficits. We found that blood from puffin chicks fed ad libitum became enriched in (15)N and (13)C compared to food-restricted chicks. Our results show that (15)N enrichment is not always associated with food deprivation and argue effects of growth on diet-tissue fractionation of nitrogen stable isotopes (Delta(15)N) need to be considered in stable isotope studies. The decrease in delta(13)C of whole blood and blood cells in restricted birds is likely due to incorporation of carbon from (13)C-depleted lipids into proteins. Effects of nutritional restriction on delta(15)N and delta(13)C values were relatively small in both experiments (delta(15)N: 0.77 and 0.41 per thousand, delta(13)C: 0.20 and 0.25 per thousand) compared to effects of ecological processes, indicating physiological effects do not preclude the use of carbon and nitrogen stable isotopes in studies of seabird ecology. Nevertheless, our results demonstrate that physiological processes affect nitrogen and carbon stable isotopes in growing birds and we caution isotope ecologists to consider these effects to avoid drawing spurious conclusions.

Parent–offspring dietary segregation of Cory’s shearwaters breeding in contrasting environments

“…We also avoided carryover maternal or egg effects by collecting blood samples relatively late in the chick-rearing period (*1 month of age). The fact that there was no evidence for severe nutritional stress at either of the study sites further reinforces the validity of our comparisons (Williams et al 2007;Sears et al 2009). …”

“…Physiological and metabolic differences among adults and chicks influence isotopic fractionation (Williams et al 2007;Harding et al 2008;Sears et al 2009) and can also contribute to parent-offspring differences in the isotopic signatures. d…”

“…15 N values can gradually change during chick growth (Williams et al 2007;Sears et al 2009) presumably due to changes in tissue turnover rates or in changes on the use of the nitrogen stored during growth (Harding et al 2008;Sears et al 2009). There are also potential carryover effects from maternal nutrients in eggs on chick isotopic signatures, and little attention has been given to this issue (Bond and Jones 2009).…”

“…Recently, SIA has provided evidence for a dietary segregation between adults and chicks in a wide range of pelagic seabirds (Hodum and Hobson 2000;Forero et al 2005;Cherel et al 2005aCherel et al , 2008Bond et al 2010;Richoux et al 2010). However, most of the mentioned studies could not assess the biological significance of the isotopic differences between adults and growing chicks (but see Cherel et al 2005a;Forero et al 2005) as isotopic fractionation differs between them, as a result of growth or nutritional stress effects (Williams et al 2007;Sears et al 2009). Additionally, the ingestion of a lipid-rich diet, as stomach oil, can deplete carbon isotopic signatures of chicks, and this has been suggested as an alternative explanation for age differences in carbon signatures (Thompson et al 2000).…”

Climate affects food availability to planktivorous least auklets Aethia pusilla through physical processes in the southeastern Bering Sea

“…Concentrations of this hormone increases predictably in response to declines in food availability (Kitaysky et al 1999a,b, 2001, Wingfield & Kitaysky 2002. This technique has been successfully applied in ecological studies of several species of seabirds , Williams et al 2007, Doody et al 2008, Welcker et al 2009), including least auklets (BenowitzFredericks et al 2008).…”