American Pikas' (Ochotona princeps) Foraging Response to Hikers and Sensitivity to Heat in an Alpine Environment

Abstract

Optimal foraging theory predicts tradeoffs in animals balancing net energy intake and predator avoidance. In particular, overall foraging activity could be low if (1) perception of predation risk is high or (2) abiotic conditions are suboptimal. American pikas (Ochotona princeps) are small, food-hoarding mammals whose foraging opportunities are restricted by heat and risk of predation. If hiking disturbance is perceived by pikas as predation risk, it could reduce the amount of food stored overwinter, possibly affecting survival. We simulated hiker disturbance events for 48 pikas in Mount Revelstoke and Glacier National Parks, British Columbia, to estimate foraging time lost due to hikers. We tested risk avoidance hypotheses using four indicators of risk behavior: alert distance (DA), flight initiation distance (DF), exit delay (TE), and delay in return to forage (TR). All hiker disturbance events elicited antipredator behaviors in foraging pikas and reduced foraging time; however, when compared to increasing temperatures over 4–6 hour observation periods, the latter best predicted a reduction in pikas' foraging activity. For every 1 °C increase in temperature, pika foraging activity decreased by 3%. Pikas near trails (<50 m) lost an average of 4.1 (SE = 0.6) minutes of foraging time per disturbance event compared to 13.2 (SE = 1.7) minutes lost by pikas with territories >100 m away from trails. Such differences might reflect habituation in pikas undergoing frequent disturbance. Monitoring pika populations for declines would be sensible given projected trends in warming climate and potential increases in hiking traffic.