Spatial orientation on a vertical maze in free-ranging fox squirrels (Sciurus niger).

Abstract

To determine how squirrels return to remembered locations in an arboreal environment, wild fox squirrels (Sciurus niger) were trained on an outdoor vertical maze. Squirrels were trained on 1 route and tested with all routes accessible. Possible mechanisms of spatial orientation were distinguished with manipulations such as rotations, shifts, and blocked routes. Squirrels consistently used an extra-maze, allothetic frame of reference to orient and appeared to organize their memory of the route hierarchically. This study demonstrates that a laboratory technique, the maze, can be successfully brought into the field to measure mechanisms of spatial orientation under natural conditions in free-ranging wild rodents. Such studies will allow researchers to determine what kind of spatial information is acquired by wild animals under natural conditions and how this information is used. The coding of space by the rodent has been at the heart of many controversies in comparative psychology, starting with the debate over place versus response learning (Hull, 1934; Tolman, 1948) and continuing in the debate over the role of the hippocampus in computing a cognitive map (Eichenbaum, Cohen, Otto, & Wible, 1992; Munn, 1950; Nadel, 1991; O'Keefe & Nadel, 1978; Olton, Becker, & Handelmann, 1979). Yet despite decades of study, determining precisely how rodents create maps of their environment is still controversial (McNaughton et al., 1996), perhaps because animals do not use a single mechanism or strategy but rely on multiple, redundant sets of cues for spatial orientation (Schone, 1984; Wehner, Michel, & Antonsen, 1996). Cues used in spatial orientation range from the simple beacon that coincides with the goal, to local cues that are associated with a distance from the goal, to the incorporation of many cues into an external frame of reference within which a rodent may relate one object to another (Collett, Cartwright, & Smith, 1986). The frame of reference may be of two types: ideothetic (i.e., egocentric), in which positions