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Mahoney, S.P.; Lewis, K.P.; Weir, J.N.; Morrison, S.F.; Luther, J.G.; Schaefer, J.A.; Pouiot, D.; Latifovic, R.
Woodland caribou calf mortality in Newfoundland: insights into the role of climate, predation and population density over three decades of study
2016  Population Ecology (58): 91-103

The rates and causes of juvenile mortality are central features of the dynamics and conservation of large mammals, like woodland caribou (_Rangifer tarandus caribou_ (Gmelin, 1788)), but intrinsic and extrinsic factors may be modified by variations in animal abundance. We tested the influences of population size, climate, calf weight and sex on survival to 6 months of age of 1241 radio-collared caribou calves over three decades, spanning periods of population growth (1979-1997) and decline (2003-2012) in Newfoundland, Canada. Daily survival rates were higher and rose more quickly with calf age during the population growth period compared to the decline. Population size (negatively) and calf weight (positively) affected survival during the decline but neither had a detectable influence during the growth phase. Sex, climate and plant productivity (the latter two derived from the North Atlantic Oscillation and Normalized Difference Vegetation Index, respectively) exerted minimal influence during either phase. Predation was the dominant source of mortality. The mean percentage of calves killed by predators was 30 % higher during the decline compared to the growth phase. Black bears (_Ursus americanus_) and lynx (_Lynx canadensis_) were the major predators during the population increase but this changed during the decrease to black bears and coyotes (_Canis latrans_). Our findings are consistent with the hypothesis that Newfoundland caribou experienced phase-dependent survival mediated proximally by predation and competition for food.

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