Are migrant and resident elk (Cervus elaphus) exposed to similar forage and predation risk on their sympatric winter range?
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Partially migratory populations, where one portion of a population conducts seasonal migrations (migrants) while the other remains on a single range (residents), are common in ungulates. Studies that assess trade-offs between migratory strategies typically compare the amount of predation risk and forage resources migrants and residents are exposed to only while on separate ranges and assume both groups intermix completely while on sympatric ranges. Here we provide one of the first tests of this assumption by comparing the amount of overlap between home ranges of GPS-collared migrant and resident elk and fine-scale exposure to wolf predation risk and forage biomass at telemetry locations on a sympatric winter range in west-central Alberta, Canada. Overlap between migrant and resident home ranges increased throughout the winter, and both groups were generally intermixed and exposed to equal forage biomass. During the day, both migrants and residents avoided predation risk by remaining in areas far from timber with high human activity, which wolves avoided. However, at night wolves moved onto the grasslands close to humans and away from timber. Resident elk were consistently closer to areas of human activity and further from timber than migrants, possibly because of a habituation to humans. As a result, resident elk were exposed to higher night-time predation risk than migrants. Our study does not support the assumption that migrant and resident elk are exposed to equal predation risk on their sympatric range when human presence alters predation risk dynamics and habituation to humans is unequal between migratory strategies.
KeywordsHabituation Home-range overlap Partial migration Ungulates Wolf predation
The project was funded by the Alberta Conservation Association, Alberta Cooperative Conservation Research Unit, Alberta Enhanced Career Development, Alberta Sustainable Resource Development, the Canon National Parks Science Scholarship for the Americas (MH), Center for Mathematical Biology, Challenge Grants in Biodiversity, Foothills Model Forest, Foundation for North American Wild Sheep, Marmot, Mountain Equipment Co-op Environment Fund, National Sciences and Engineering Research Council CRO grant no. 261091-02, Parks Canada, Patagonia, Rocky Mountain Elk Foundation, Sundre Forest Products Limited, Weyerhauser Inc., and the University of Alberta. We thank the Ya Ha Tinda Ranch staff and the biologists of Parks Canada and Alberta Fish and Wildlife. For their valuable feedback during the preparation of this manuscript, we thank C. Cassady St. Clair, R. Hudson, and C. White. Finally, we thank B. van Moorter for helping us develop code in R to calculate the volume of intersection index.
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