Snow depth does not affect recruitment in a low-density population of boreal woodland caribou (Rangifer tarandus caribou)
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Winter snow depth may be an important driver of annual variability in recruitment of ungulate calves, and low calf recruitment has been implicated as a factor in declining boreal caribou (Rangifer tarandus caribou) populations. We used 11 consecutive years (2006–2016) of aerial survey data to document calf recruitment in a low-density population of boreal woodland caribou in the Northwest Territories, Canada. We measured snow depth in winter and tested two hypotheses: (1) that calf recruitment was lower in winters with greater snow depth and (2) that calf recruitment was lower following winters with greater snow depth (1-year time lag). Recruitment, the number of calves/adult female in March, ranged twofold from 0.23 to 0.45, and snow depth also ranged twofold from 41 to 85 cm. Yet, we found no support for the hypothesis that late-winter snow depth in the current or previous year was inversely related to calf recruitment.
KeywordsCalf recruitment Caribou Northwest Territories Rangifer tarandus Snow depth
We thank Diversified Environmental Services for taking snow depth measurements. Great Slave Helicopters provided skillful pilots for the caribou classification surveys. We thank our First Nations partners for their support of this study: Sambaa K’e Dene Band (Trout Lake), Fort Simpson Métis Local, The Denendeh Harvesters Committee of Líídlíí Kue First Nation (Fort Simpson), Jean Marie River First Nation, Pehdzeh Ki First Nation (Wrigley), Nahanni Butte Dene Band, Acho Dene Koe Band (Fort Liard), and Ka’a’gee Tu First Nation (Kakisa). Funding was from the Northwest Territories Western Biophysical Program, the Department of Environment and Natural Resources (GNWT), and the Cumulative Impacts Monitoring Program. Two anonymous reviewers provided comments on an earlier draft that improved this paper.
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