Predation shapes the movement of a well-defended species, the North American porcupine, even when nutritionally stressed

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Abstract

Animals reduce their exposure to predation often at the cost of nutritional inputs. A variety of predator avoidance strategies exist, but species generally exist along a spectrum with some primarily utilizing behavioral responses to avoid predation and others relying more on morphological defenses to deter predation. North American porcupines (Erethizon dorsatum) possess a well-developed predator deterrent strategy (i.e., quills). During the winter, porcupines enter a nutritional bottleneck where they principally rely on endogenous stores to survive winter. We hypothesized that porcupine behavior in winter would, then, be primarily driven by nutritional demands rather than predation risk. To test this trade-off between perceived risk of predation and nutritional stress, we analyzed the length and sinuosity of movement patterns, relative to nutritional condition (urinary urea: creatinine), snow conditions (depth, density), and a risk landscape (predation risk and refuges). As predicted, the sinuosity of movement paths was unrelated to any of our variables, but we detected a strong correlation between lengths of movements with risk landscape. Specifically, the length of porcupine movement declined as the average risk of predation increased, and the presence of refuge trees in their movement path was positively related to path length. Thus, even for animals possessing extreme morphological defenses effective at deterring predation, and during a period of nutritional stress, movement and behavior are nevertheless driven by perceived predation risk.

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