Beaver (Castor fiber) activity patterns in a predator-free landscape. What is keeping them in the dark?

Activity patterns play an important role in the fitness of animals. Energy conservation, physiological adaptations, prey availability, competition, and predation caused by predators and humans are all important parameters influencing when, and where, animals are active. Over time, however, a change in such external factors can lead to a shift in optimal activity patterns. In this paper, we use camera traps to study the daily activity patterns of Eurasian beavers (Castor fiber) reintroduced into an atypical, predator-free landscape. We explore if and how beavers have adjusted their activity patterns in the absence of predators, and whether this varies with day length and moonshine. Our results reveal that beavers in our study area have a mainly crepuscular and nocturnal activity pattern, similar to animals in more natural landscapes with predators. Changes in day length had only a limited effect on the duration of beavers’ activity, but, contrary to our expectations, beaver activity increased during bright moonlight. Activity patterns were also clearly bimodal during nights with bright moonlight, but unimodal during dark nights. The shape of their activity pattern did change throughout the year. These results suggest that beavers can alter their activity patterns in response to external cues, but that the current absence of predators has not resulted in a relaxation of their nocturnal activity patterns. We discuss our results in light of historical human persecution and suggest that beaver activity patterns continue to be influenced by ghosts of predators past.