Vigilance as a benefit of intermittent locomotion in small mammals

In many animal species, locomotion is frequently interrupted by brief pauses. This intermittent locomotion is usually considered a mode of prey search, but other possible functions include reduced detection or attack by predators and improved endurance. We tested the hypothesis that pauses also serve to improve vigilance for predators in two species of sciurid rodent. Videotaping animals travelling between food-collecting and food-hoarding sites revealed that numerous short pauses comprise 5-38% of the time spent 'moving' in grey squirrels, Sciurus carolinensis, and 0-41% in eastern chipmunks, Tamias striatus. In this situation, search for food items did not occur, and pausing did not reduce the total time spent as a moving stimulus for predators. It also appeared that speed while running was too slow and the pauses too brief to provide an endurance advantage. As predicted by the vigilance hypothesis, both species spent more time pausing when moving away from forest cover (presumably towards areas of higher risk) than when travelling back towards forest cover. In control trials within forest cover, squirrels did not differ in time pausing when approaching and leaving patches, but chipmunks paused more when approaching patches than when leaving them. We conclude that one function of pausing in squirrels is to improve anti-predator vigilance. The occurrence of pausing by chipmunks did not match a priori predictions of the vigilance hypothesis. Because it also failed to match predictions of previous alternative hypotheses, we suggest that studies are needed to examine whether the risk of attacks by conspecifics and predators is higher for chipmunks approaching than leaving food patches in forest habitat. (C) 1998 The Association for the Study of Animal Behaviour.