Influence of environment structure and food availability on the foraging behaviour of the laboratory rat

According to the optimal foraging theory, an animal is expected to enter into a given activity depending on associated costs and benefits. In line with this assumption, numerous studies have suggested that energetic reward is balanced by predation risk in foraging decisions. Therefore, the use of information about indirect cues of predation risk such as physical structure (e.g. cover, escape substrate) can give individuals a selective advantage. We studied foraging behaviour in the laboratory rat in an experimental maze; it allowed us to vary two environmental parameters: food availability and physical structure. In a first experiment, rats were offered a choice between two areas only differing in cover density. In a second experiment, the two areas only differed in food density. In a third experiment, we crossed both parameters. Our results showed that high "cover" patch was preferentially exploited (experiment 1) and that rats foraged more in the high food density patch (experiment 2). The last experiment showed that rats partially trade-off between cover density and food availability, even if the safest area was still preferred. Therefore, we suggest that foraging decisions depend primarily on safety needs, rather than food availability, at least when animals are not severely food-deprived. (C) 2002 Elsevier Science B.V. All rights reserved.