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Group living in animals is believed to confer advantages related to a decrease in predation risk and an energetic trade-off between vigilance and foraging efficiency. Eight Gunnison’s prairie dog, Cynomys gunnisoni, colonies in Flagstaff, Arizona (elevation 2300 m), were studied from April to August 2000 to examine the adaptive significance of colonial living in the context of predation risk and antipredator behavioral strategies. Each colony was sampled once every 10 days for a period of 3 h. Upright and quadrepedal vigilance was recorded using scan samples. All predation events were recorded. Results suggest that vigilant behavior in Gunnison’s prairie dogs is an antipredator strategy because the animals oriented more frequently towards the periphery of the colony while vigilant. Gunnison’s prairie dogs engaged in posting, an upright bipedal posture, more frequently than scanning, a quadrepedal posture. Furthermore, there was no relationship between either form of vigilance and population size. The proportion of animals vigilant decreased significantly only on the two smallest colonies as colony size increased. On larger colonies there was no relationship between the proportion of animals vigilant and colony size. The lack of change in the proportion of animals vigilant in larger populations may be a function of perceived risk rather than actual individual risk.


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