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An isotopic approach to measuring nitrogen balance in caribou

Authors

  • David D. Gustine,

    Corresponding author
    1. Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA
    • Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.
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  • Perry S. Barboza,

    1. Institute of Arctic Biology, Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA
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  • Layne G. Adams,

    1. U.S. Geological Survey, Alaska Science Center, 4210 University Dr., Anchorage, AK 99508-4626, USA
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  • Richard G. Farnell,

    1. Yukon Department of Environment (retired), PO Box 2703, Whitehorse, Yukon, Canada Y1A 2C6
    Current affiliation:
    1. 90847 Alaska Highway, Whitehorse, Yukon, Canada Y1A 5S8.
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  • Katherine L. Parker

    1. Natural Resources and Environmental Studies Institute, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9
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  • Associate Editor: Steeve Côté

Abstract

Nutritional restrictions in winter may reduce the availability of protein for reproduction and survival in northern ungulates. We refined a technique that uses recently voided excreta on snow to assess protein status in wild caribou (Rangifer tarandus) in late winter. Our study was the first application of this non-invasive, isotopic approach to assess protein status of wild caribou by determining dietary and endogenous contributions of nitrogen (N) to urinary urea. We used isotopic ratios of N (δ15N) in urine and fecal samples to estimate the proportion of urea N derived from body N (p-UN) in pregnant, adult females of the Chisana Herd, a small population that ranged across the Alaska-Yukon border. We took advantage of a predator-exclosure project to examine N status of penned caribou in April 2006. Lichens were the primary forage (>40%) consumed by caribou in the pen and δ15N of fiber tracked the major forages in their diets. The δ15N of urinary urea for females in the pen was depleted relative (−1.3 ± 1.0 parts per thousand [‰], equation image) to the δ15N of body N (2.7 ± 0.7‰). A similar proportion of animals in the exclosure lost core body mass (excluding estimates of fetal and uterine tissues; 55%) and body protein (estimated by isotope ratios; 54%). This non-invasive technique could be applied at various spatial and temporal scales to assess trends in protein status of free-ranging populations of northern ungulates. Intra- and inter-annual estimates of protein status could help managers monitor effects of foraging conditions on nutritional constraints in ungulates, increase the efficiency and efficacy of management actions, and help prepare stakeholders for potential changes in population trends. © 2010 The Wildlife Society.

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