Foraging range in mice and voles: the role of risk

The significance of risk assessment in determining the boundaries of foraging ranges of deer mice and voles was examined by comparing the distances to which resident animals were willing to follow shifting feeding stations providing equal rewards beyond their previous foraging ranges in an area with abundant cover (forest), and in one where cover was lacking (frozen lake surface). Previous foraging ranges were estimated on the basis of livetrapping and the "rediscovery distances" for the moving stations. In three experiments the distance at which animals stopped visiting the stations ("giving-up distance") averaged 3.3 times farther where cover was abundant (forest) than where it was absent (lake). In a fourth experiment, reduction of supplementary food available within the original ranges extended the giving-up distance where cover was present but had relatively little effect on giving-up distance and almost no effect on rediscovery distance where cover was absent. Supplying cover more than tripled giving-up distances on the lake. The distance at which boxes were visited was affected by snowfall, ambient temperature, food supply, and availability of cover. Results emphasize the importance of risk assessment in defining foraging range, and suggest that hoarding permits choice among energy maximization and time minimization strategies.