Use of Middens by Red Foxes: Risk Reverses Rhythms of Rats

Although Norway rats (Rattus norvegicus) generally are nocturnal, we have found a wild population showing diurnal activity. Three hypotheses could account for this aberrant behavior: subordinate rats forage diurnally to avoid dominant individuals; minimal disturbance facilitates diurnal activity; rats avoid predation by nocturnal red foxes (Vulpes vulpes). To test predictions generated by these hypotheses, we studied activity and movement patterns of rats and foxes and found that only the predictions of the predator-avoidance hypothesis were fulfilled. We then tested this hypothesis experimentally by keeping rats captured from the diurnal population in a fox-proof enclosure. Rats in the enclosure reverted to normal nocturnal behavior. We believe, therefore, that rats timed their activity to avoid predation from foxes. Our results provide the first example of a mammalian prey species altering the timing of its foraging to avoid a predator.