Diet-tissue discrimination factors of carbon and nitrogen stable isotopes in blood of Snowy Owl (Bubo scandiacus)

Analysis of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) stable isotope ratios (hereafter delta(13)C and delta(15)N, respectively) in animal tissues is a powerful tool in food-web studies. However, isotopic ratios of prey are not transmitted directly to a consumer, as a diet tissue discrimination factor (denoted Delta) occurs between sources and consumer's tissues. An accurate assessment of the diet of a consumer with stable isotopes thus requires that the Delta(13)C and Delta(15)N of the studied species are known. Our aim was to establish Delta(13)C and Delta(15)N values in the Snowy Owl (Bubo scandiacus (L., 1758)). Moreover, we assessed the potential effect of ethanol preservation of blood samples on delta(13)C and delta(15)N values. We kept four captive adult Snowy Owls on a pure diet of mice for >= 6 weeks. We then collected mouse muscle and blood samples from the owls and analyzed their delta(13)C and delta(15)N values. Delta(13)C and Delta(15)N values (mean +/- SE) for owl blood were +0.3 parts per thousand +/- 0.2 parts per thousand and + 1.9 parts per thousand +/- 0.1 parts per thousand, respectively. These values are the first discrimination factors ever reported in Strigiformes and are lower, for Delta(15)N, than those obtained in terrestrial carnivores and other bird species, including falcons. Preservation in ethanol did not significantly affect delta(13)C and delta(15)N values.