Abstract
Tracking data from voles (Microtus pennsylvanicus) and from its occasional predator, the short-tailed shrew (Blarina brevicauda), confined together in an outdoor enclosure (20 by 40 meters), demonstrated that voles tend to avoid places frequented by shrews. Laboratory tests indicated that voles avoid shrews more than they avoid laboratory mice and that a vole's response to a shrew is similar to its response to shrew odor. One of the testing procedures generated U-shaped curves of exploratory behavior.