Rodents usually respond to the presence of owls by reducing overall activity, in particular foraging. In this study, a playback of recorded tawny owl, Strix aluco, calls was sufficient to induce a marked effect in the social (Gunther's) vole, Microtus socialis. Some of the voles exposed to owl calls reduced their activity ('freeze' pattern) unlike control voles exposed to a human voice. Other voles, however, dashed around the cage ('flee' pattern). Owl calls also increased corticosterone levels in the voles, showing that the calls induced stress. We suggest that the behavioural dichotomy to freeze or flee in voles is a result of differences in individual normal behaviour and/or in stimulus interpretation. In the common spiny mouse, Acomys cahirinus, no behavioural changes were detected after exposure to owl calls, despite increased cortisol levels which are indicative of stress. Differences in the habitats of voles and spiny mice may explain the apparent lack of behavioural response in the latter. They are rock-dwelling rodents preferentially foraging between boulders and in rock crevices, where they are relatively protected from aerial predation, whereas voles forage in relatively open spaces. Copyright 1999 The Association for the Study of Animal Behaviour.