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

Abstract

Analysis of carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios (hereafter δ13C and δ15N, 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 Δ) occurs between sources and consumer’s tissues. An accurate assessment of the diet of a consumer with stable isotopes thus requires that the Δ13C and Δ15N of the studied species are known. Our aim was to establish Δ13C and Δ15N values in the Snowy Owl ( Bubo scandiacus (L., 1758)). Moreover, we assessed the potential effect of ethanol preservation of blood samples on δ13C and δ15N 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 δ13C and δ15N values. Δ13C and Δ15N values (mean ± SE) for owl blood were +0.3‰ ± 0.2‰ and +1.9‰ ± 0.1‰, respectively. These values are the first discrimination factors ever reported in Strigiformes and are lower, for Δ15N, than those obtained in terrestrial carnivores and other bird species, including falcons. Preservation in ethanol did not significantly affect δ13C and δ15N values.

Variability in stable isotopes of snowy owl feathers and contribution of marine resources to their winter diet

“…We took a 1‐ml blood sample from the brachial vein of each individual with a syringe and immediately transferred it to a 70% ethanol‐filled Eppendorf tube kept frozen at –20°C. Ethanol does not significantly alter carbon and nitrogen isotopic composition of tissues (Hobson et al , Therrien et al ). In the laboratory, blood samples were freeze‐dried at –50°C for 72 h and ground to a fine powder with mortar and pestle.…”

“…The mean δ 13 C and δ 15 N values of prey items were subtracted from the δ 13 C and δ 15 N values of each individual's feather (ΔX = Δ tissue –Δ diet ) to obtain the resulting discrimination factor of feathers (ΔX). For blood, discrimination factors from Therrien et al () were used.…”

“…Discrimination factors for feathers (this study) and blood (Therrien et al ) were accounted for in all models and statistical analyses were performed using R 3.2.2 software (R Core Team). Results are presented as means ± SD, unless otherwise stated.…”

Foraging behaviour of Magellanic Penguins during the early chick‐rearing period at Isla de los Estados, Argentina

“…Blood was preserved in 70% ethanol until later processing in the laboratory. Several studies in the past showed little effect of alcohol preservation on the stable isotope values of whole blood (Hobson et al 1997, Halley et al 2008, Therrien & Fitzgerald 2011, but see Bugoni et al 2008. We checked nests of equipped Penguins every week until the end of the fieldwork to determine chick survival.…”

Stable isotopes identify age- and sex-specific dietary partitioning and foraging habitat segregation in southern giant petrels breeding in Antarctica and southern Patagonia

“…In Antarctica, we caught adults and chicks (50-60 days old) on their nests, took about 0.3 ml of whole blood from the foot vein, and transferred it to 2 different vials containing 1.5 ml of 70 % ethanol from a common source and stored for later analysis. Storage in 70 % ethanol has been generally found to not affect the stable isotope values of whole blood (Hobson et al 1997;Halley et al 2008;Therrien et al 2011; though see Bugoni et al 2008).…”