Illumination and the perception of remote habitat patches by white-footed mice.

Perceptual range, or the distance at which habitat 'patches' can be perceived, constrains an animal's informational window on a given landscape. If such constraints are great, they may limit successful dispersal between distant habitat patches. On dark nights, nocturnal white-footed mice, Peromyscus leucopus, have surprisingly limited perceptual abilities regarding distant forested habitat. In fact, their ability to orient towards such habitat while travelling in a bare agricultural field indicates a perceptual range under 30 m. However, increasing illumination can increase perceptual range. For example, full moonlight extends the perceptual range of mice to about 60 m. Light levels at dusk (twilight) extend perceptual range still further to about 90 m. These results suggest that interpatch dispersal by white-footed mice would be more successful under greater illumination, but travelling under such conditions entails a considerable risk of predation. These mice might avoid such a conflict by travelling under the cover of darkness with the aid of information gathered remotely during relatively high illumination. We show that mice are indeed capable of such a 'look now and move later' strategy: mice retain directional information gained under bright conditions and maintain a previously determined bearing in conditions under which distant navigational stimuli may be largely absent (e.g. maximal darkness). Ultimately, a better understanding of the behavioural and ecological factors affecting the movements of animals across landscapes should produce a clearer picture of the interaction between landscape structure and population ecology. Copyright 1999 The Association for the Study of Animal Behaviour.