COS 202-4 - Can carnivore scent cues shape a landscape of fear in large herbivores?

Abstract: Throughout the U.S., populations of large mammalian herbivores, such as white-tailed deer, persist above desired densities. High-density herbivore populations are typically a result of reduced or absent predator populations in conjunction with anthropogenic changes that favor herbivore foraging. Direct predation (i.e., consumption) by carnivores reduces herbivore populations and can potentially mitigate issues that are caused by high-density herbivore populations via population reduction and decreasing juvenile recruitment. Less understood is the effect that predator cues (i.e., scent) have on the behavior and habitat use of large herbivores that are olfaction-oriented. We designed an experiment with the objective of uncovering whether predator-scent cues affect herbivore landscape use and behavior in two regions of western Wyoming. Additionally, we wanted to discern if herbivores that more frequently encounter predators respond differentially to scent cues than herbivores that experience minimal predation.



During the summer and autumn of 2022, we placed 20 motion-sensing, infrared cameras in riparian sites near Cody, WY (high predator density) and Pinedale, WY (low predator density) for three months. For the first month, we left cameras undisturbed to measure the natural detection rates of wildlife at each camera location. We then applied one of four carnivore-scent treatments (wolf, coyote, or mountain lion urine, or a control/water) every five days for an additional month. After treatment applications had ceased, we again measured the detection rates of wildlife at each camera to discern how long any effects of the treatments persisted. We used a negative binomial regression to model whether the detection rate of herbivores varied among sampling phases and treatment types during the phase when urine was applied. We confirmed that carnivores are more abundant and that there is a greater diversity of carnivore species present at the Cody site, indicating that herbivores in Cody experience the direct threat of predators more frequently. Preliminary results suggest that herbivores did not differentiate between scent cues depending on carnivore species. Furthermore, the detection rate of herbivores at Pinedale decreased in response to carnivore-scent cues more than in Cody. These results suggest that herbivores that do not experience a high degree of predation exhibit an increased fear response to the indirect presence of carnivores. This shows that herbivores may alter their landscape use and resource selection in areas where carnivore populations are being re-established.