Gradients of predation risk affect distribution and migration of a large herbivore
Grigg, Jamin Lyle.
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Few studies have placed wildlife behavioral responses to human disturbance and hunting pressure within the larger ecological context of predator-prey theory. Given that large herbivores respond behaviorally to the presence of wolves and other predators, we should expect similar adaptive behavioral responses when large herbivores are presented with risk in the form of human disturbance and hunting pressure. One index of human access, disturbance, and thus potential predation risk to large herbivores from hunters are road and trail networks bisecting large herbivore ranges. I evaluated the effects of human disturbance and predation pressure in the forms of motorized and total combined access networks on elk (Cervus elaphus) summer home range size, timing of fall migration, and movement rates by placing 49 GPS radio-collars on adult female elk on a winter range in the Madison Valley, MT over the course of a two-year study. I found evidence that elk responded to motorized access during the summer by increasing summer home range size.Further, regional variation in predation risk from human hunters resulted in elk subjected to the highest levels of hunting pressure initiating fall migration from summer ranges to winter ranges earlier than elk subjected to lower levels or no hunting pressure. These winter ranges are mostly privately-owned ranchlands that provide relative refuge from hunting pressure. All elk in this study summered on public lands, yet most elk summering in heavily hunted regions were unavailable to public-land hunters for large portions of the hunting seasons due to early fall migration patterns. Movement rate models were ambiguous and I was unable to detect differences associated with motorized and total access levels, though movement rates during the hunting seasons were correlated with varying regional predation risk. This research potentially provides valuable knowledge to biologists across the western United States managing large herbivore populations that summer on public lands and winter in privately-owned agricultural valleys, and provides insight into general predator-prey behavioral relationships.