The balancing act of foraging: mammalian herbivores trade-off multiple risks when selecting food patches.

Abstract

Animals face multiple risks while foraging such as the risk of acquiring inadequate energy from food and the risk of predation. We evaluated how two sympatric rabbits (pygmy rabbits, Brachylagus idahoensis, and mountain cottontail rabbits, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush-steppe of western North America respond to different types and levels of perceived risks (i.e., fitness cost × probability of occurrence), including fiber and toxins in food, exposure to predation, and distance from a refuge. We measured food intake by the rabbits at paired food patches that varied in these risks and used the method of paired comparisons to create a relative ranking of habitat cues, which revealed an animal's perceived risk on a single scale representing an integrated response to a variety of risks. Pygmy rabbits perceived exposure to predation risk and distance from a burrow as riskier than did cottontails, whereas cottontails perceived dietary toxin as riskier. Pygmy rabbits consumed lower quality food, containing higher fiber or toxins, thereby avoided feeding in exposed patches or traveling far from their burrow to forage. In contrast, cottontails fed in exposed patches and traveled farther from the burrow to obtain higher quality food. We have shown how risks can be integrated into a single model that allows animals to reveal their perceptions of risks on a single scale that can be used to create a spatially explicit landscape of risk.