Sociality and movement change through space and time: implications for anti-predator strategies in caribou

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Risk could vary temporally with predator activity levels or as animals age. While risk could vary spatially as a function of habitat complexity, where open habitats are risky because prey are more visible to predators. Prey, such as caribou ( Rangifer tarandus (Linnaeus, 1758)), attenuate predator risk by altering behaviour through space and time. We tested the “risky times” and “risky places” hypotheses to investigate how sociality can mitigate putative risk during risky times and in risky places. We predicted that caribou are social in risky times (e.g., night and calving) because their predators are primarily nocturnal and newborn calves are vulnerable. We also predicted that sociality is higher in open habitats at nighttime relative to closed habitats at nighttime to mitigate risk during a riskier time and place. We used location data collected from global positioning system collared caribou in Newfoundland to generate social networks to estimate sociality. In winter, caribou were more social at night than during the day. During the night, caribou were more social in open habitat than in forested habitat, indicating a potential trade-off between selecting open foraging habitat and the risk of predation. We illustrate that sociality mitigates risky times and risky places.