Beaver foraging behaviour: Seasonal foraging specialization by a choosy generalist herbivore

Classical theory states that generalist foragers should specialise to maximise their net energy intake on a temporal basis. Within broad distributions, generalists select optimal food sources; however, the availability and representation of selected food items in the diets of generalist consumers vary geographically. Conversely, specialists, within their entire range, concentrate on specific food resources, and their diets remain constant in varying environments. The distributions of highly palatable food resources might influence the foraging patterns of species with opportunistic foraging behaviours. We used the Eurasian beaver (Castor fiber) as a model for what is considered an opportunistic generalist herbivore. We analysed whether the beavers’ foraging pattern could show specialisation. Five beaver populations living in diverse environments were evaluated, and their diet choices for overwintering were examined. Our data indicated low proportions of generality with regard to the beavers’ foraging behaviours. Within 110 territories, we observed that beavers did pursue choosy opportunistic strategies, though only to a small extent. Although we confirmed the established knowledge that beavers prefer to browse mainly poplars and willows, we also found that, contrary to many published studies, their preferences occurred regardless of riparian vegetation composition. While the beavers examined in this study preferred six genera of woody vegetation, we argue that they may have been inclined primarily to use two genera with regard to both food choice and spatial territory placement. Thus, the opportunistic feeding behaviours of generalists observed in this study may be influenced by evaluation under varying conditions.