How does the rat (Rattus norvegicus) adjust food -carrying responses to the influences of distance, effort, predatory odor, food size, and food availability?

Abstract

Foraging animals will behave in such a way that they maximize foraging efficiency while minimizing risk to predation. Using a behavioral paradigm in which laboratory rats (Rattus norvegicus) were provided with food at one end of an elevated beam and a refuge to which they could carry the food at the other end of the beam, we examined the effects of travel distance, travel difficulty, ambient lighting, predation risk, and food size on foraging behavior. Both lengthening travel distance (by increasing beam length) and increasing travel difficulty (by decreasing beam width) decreased food carrying. When plotted as a function of travel time, the effects of the two treatments appeared to be partly different. Decreasing ambient illumination decreased food carrying, although the rats still responded to distance and food size. In contrast, predator’s odor (cat) stopped foraging altogether. When a store of small food pellets was available, the rats ate for prolonged periods in the open, and eating time increased with travel distance; however, when large food pellets were also available, the rats immediately selected and carried them to the refuge. The experiments show that food-carrying behavior in the rat is influenced by a variety of independently acting factors, which include eating time, food size, travel distance, travel risk, illumination, predation, and exposure time. The varied and flexible foraging behavior of the animals is discussed in relation to optimal foraging theory.