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Nutritional stress and body condition in the Great Gray Owl (Strix nebulosa) during winter irruptive migrations

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The largest irruptive migration of the Great Gray Owl (Strix nebulosa Forster, 1772) recorded since 1831 occurred in Minnesota, USA, during the winter of 2004–2005. We tested the hypothesis that morphometric indicators of nutritional stress covary with stable isotope signatures in a sample of 265 owls killed by vehicle collisions. The ratio of carbon to nitrogen in muscle (C/Nmuscle) was shown to be a reliable proxy of nutritional stress. δ13C values for liver and muscle were significantly higher in owls in poor condition, reflecting the depletion of lipid reserves in fasting individuals. On the other hand, δ15N values for liver and muscle were marginally lower or unchanged in owls in poor condition. Stomachs of emaciated owls were less likely to contain prey, implying that many nutritionally stressed individuals were too weak to hunt and were near the tipping point of irreversible fasts. In a broader context, sexual differences in the correlative relationships between stable isotope signatures, C/N, and body condition suggest that the consequences of reversed sexual size dimorphism extend to physiological processes during the nonbreeding season.

Keywords: C/N; Great Gray Owl (Strix nebulosa); Minnesota; azote; body mass index; carbon; carbone; chouette lapone (Strix nebulosa); dimorphisme sexuel inversé de la taille; famine; fasting; indice de masse corporelle; isotopes stables; jeûne; nitrogen; reversed sexual size dimorphism; stable isotopes; starvation

Document Type: Research Article


Affiliations: 1: Department of Vertebrate Zoology, MRC-116, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington, DC 20013-7012, USA; Center for Macroecology, Evolution and Climate, University of Copenhagen, DK-2100, Copenhagen Ø, Denmark. 2: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road Northwest, Washington, DC 20015, USA; Department of Zoology and Physiology, University of Wyoming, 1000 East University Avenue, Department 3166, Laramie, WY 82071, USA. 3: Zoology Department, Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605-2496, USA. 4: Superior National Forest, 2020 West Hwy 61, Grand Marais, MN 55604, USA. 5: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road Northwest, Washington, DC 20015, USA; State University of New York College of Environmental Science and Forestry, SUNY-ESF, 1 Forestry Drive, Syracuse, NY 13210, USA. 6: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road Northwest, Washington, DC 20015, USA.

Publication date: 2012-07-19

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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