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

Abstract

The snowy owl is an elusive arctic predator known for its nomadic behaviour. Satellite tracking has revealed that some adult snowy owls could make an extensive use of the marine environment during the non‐breeding season. However, the relative contribution of marine resources to their diet is unknown. Stable isotope analyses can be useful to document the diet of mobile animals during periods of the year when individuals are less accessible. This study aimed to assess variation in isotopic values (δ13C and δ15N) of various feather types, and the usefulness of feathers to determine the contribution of the marine environment to the winter diet of snowy owls captured in summer. We sampled feathers coming from 6 body regions of 18 breeding females at two sites in the eastern Canadian Arctic in 2013 and 2014. Prior to analyses, diet‐tissue discrimination factors of snowy owl feathers were established in captivity. Variability in isotopic values among feather types was relatively low and pairwise correlations in isotopic values between feathers on the same individual were variable and often low, which suggests differences in the diet at the time when various feathers were synthesized. Diet reconstruction models detected a contribution of marine sources to snowy owl feathers ranging from 4 to 19% among feather types. However, the marine contribution was highly variable when single feathers were examined within individuals, ranging from 3 to 71%. This indicated that no single feather type could be used alone to reliably infer the contribution of marine resources to the winter diet of owls, possibly due to a high variability in the timing and sequence of molt. For asynchronous molters like snowy owls, we recommend sampling multiple feathers from various body regions, excluding wing feathers, to investigate winter diet or habitat use.

Wintering space use and site fidelity in a nomadic species, the snowy owl

“…For instance, although snowy owls are regular winterers in the Canadian Prairies and American Great Plains, they also show periodic irruptions throughout the temperate regions of North America (Kerlinger et al 1985, Kerlinger and Lein 1988, Holt et al 2015. Many adult snowy owls also remain in the Arctic throughout the winter and can make extensive use of the marine environment , Robillard et al 2017). However, very little is known about individual consistency and the effect of environmental factors on patterns of space and habitat use during the winter in such nomadic species.…”

“…Ptarmigans and hares can also be part of their wintering diet (Holt et al 2015, Doyle et al 2017. Owls wintering in coastal and marine environments can rely on other prey such as water and sea birds (Campbell and Maccoll 1978, Smith 1997, Robertson and Gilchrist 2003, Robillard et al 2017. These prey can often be found in high densities Robertson 2000, Therrien et al 2011) in open water in the sea ice (e.g.…”

Stable isotopes reveal unexpected relationships between fire history and the diet of Spotted Owls

“…We corrected for trophic discrimination (d 13 C AE sd: 1.88& AE 0.04; d 15 N AE sd: 4.12& AE 0.26) based on Snowy Owl Bubo scandiacus captive-feeding trials (Robillard et al 2017). After trophic correction of prey isotopic signatures, nearly all owl isotopic signatures fell within the mixing space, suggesting that we had adequately sampled prey and applied appropriate trophic discrimination factors.…”

Under-ice limnology of coastal valley lakes at the edge of the Arctic Ocean

“…Approximately 10 mg of dry sediment was encapsulated in tin containers and combusted at a localized temperature of up to 1800°C to obtain carbon and nitrogen stable isotopic ratios by continuous-flow isotope ratio mass spectrometry, following the methods in Robillard et al (2017). The stable carbon isotope ratios are reported as δ 13 C org and δ 13 C bulk values in per mil notation (‰) relative to the V-PDB standard.…”