PREDATOR RISK AFFECTS FORAGING BEHAVIOR OF PIKAS - OBSERVATIONAL AND EXPERIMENTAL-EVIDENCE

Field observations were made on collared pikas, Ochotona collaris, in Alaska to determine whether the risk of predation affected foraging behaviour in this small, herbivorous lagomorph. Four lines of evidence suggest that pika foraging is risk sensitive. First, pikas concentrated their foraging near talus (rock piles) rather than away from it despite the increase in vegetation biomass with increasing distance from the talus. Second, juveniles increased their foraging distance from the talus to match adults after juveniles had been above ground for 2 weeks, and lactating females foraged further from the talus than when they were pregnant, exposing themselves to a greater risk, but also availing themselves of more food. Third, after an ermine, Mustela erminea, appeared, pika latency to resume foraging depended on how close the ermine had come to capturing the pika. Finally, foraging distance was altered experimentally by constructing talus 'fingers', which reduced predator risk, and by fertilizing different meadow areas, which enhanced forage value. In addtion to energy and nutrients, the risk of predation plays an important role in pika foraging behaviour. © 1991 The Association for the Study of Animal Behaviour.