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 p rey search, but other possible functions include reduced detection or attack by predators and improved endurance. We tested the hypothesis t hat pauses also serve to improve vigilance for predators in two specie s of sciurid rodent. Videotaping animals travelling between food-colle cting and food-hoarding sites revealed that numerous short pauses comp rise 5-38% of the time spent 'moving' in grey squirrels, Sciurus carol inensis, and 0-41% in eastern chipmunks, Tamias striatus. In this situ ation, search for food items did not occur, and pausing did not reduce the total time spent as a moving stimulus for predators. It also appe ared that speed while running was too slow and the pauses too brief to provide an endurance advantage. As predicted by the vigilance hypothe sis, 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, squi rrels did not differ in time pausing when approaching and leaving patc hes, but chipmunks paused more when approaching patches than when leav ing them. We conclude that one function of pausing in squirrels is to improve anti-predator vigilance. The occurrence of pausing by chipmunk s did not match a priori predictions of the vigilance hypothesis. Beca use it also failed to match predictions of previous alternative hypoth eses, we suggest that studies are needed to examine whether the risk o f attacks by conspecifics and predators is higher for chipmunks approa ching than leaving food patches in forest habitat. (C) 1998 The Associ ation for the Study of Animal Behaviour.