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Woodland caribou calf mortality in Newfoundland: insights into the role of climate, predation and population density over three decades of study

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Population Ecology

Abstract

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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Acknowledgments

We thank the Government of Newfoundland and Labrador for supporting this work and the many employees over the past 35 years who have contributed their time, knowledge and dedication. We especially thank the Wildlife Field Technicians who worked side by side with the senior author throughout more than three decades and who made this extraordinary database possible. They each gave years of their lives to illuminating the question of “Why do caribou calves die?”, often under difficult field conditions. We also especially thank Frank Norman for his quiet, competent work in managing these databases and making our jobs much easier. Paul Doherty and Jay Rotella provided advice on Program MARK and survival modeling and John Jacobs provided advice for the climate analyses. We thank David Fifield for assistance with data management and insightful comments on the manuscript. We thank Safari Club International Foundation for financial and other support during its last 5 crucial years. Finally we thank Tom Bergerud who blazed an exciting and well-illuminated trail for us to follow. The caribou of Newfoundland will always owe part of their future to him.

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Authors and Affiliations

  1. Conservation Visions Inc., Stn C, 354 Water Street, P.O. Box 5489, St. John’s, NL, A1C 5W4, Canada

    Shane P. Mahoney

  2. Sustainable Development and Strategic Science, Department of Environment and Conservation, Government of Newfoundland and Labrador, St. John’s, NL, A1B 4J6, Canada

    Keith P. Lewis & Jackie N. Weir

  3. Dryas Research Ltd., Edmonton, AB, T6C 2R6, Canada

    Shawn F. Morrison

  4. Wildlife Division, Department of Environment and Conservation, Government of Newfoundland and Labrador, Corner Brook, NL, A1A 5J7, Canada

    J. Glenn Luther

  5. Department of Biology, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada

    James A. Schaefer

  6. Canada Centre for Remote Sensing, Canada Centre for Mapping and Earth Observation, 560 Rochester Street, Ottawa, ON, K1A 0E4, Canada

    Darren Pouliot & Rasim Latifovic

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  1. Shane P. Mahoney
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  2. Keith P. Lewis
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  3. Jackie N. Weir
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Correspondence to Jackie N. Weir.

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Mahoney, S.P., Lewis, K.P., Weir, J.N. et al. Woodland caribou calf mortality in Newfoundland: insights into the role of climate, predation and population density over three decades of study. Popul Ecol 58, 91–103 (2016). https://doi.org/10.1007/s10144-015-0525-y

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