EN
Two alternative hypotheses explaining low densities of juvenile wood mice Apodemus sylvaticus (Linnaeus, 1758) early in the breeding season were compared: the Adult Aggression Hypothesis and the Habitat Saturation Hypothesis. They predict different ratios between adult and juvenile densities, which were tested using trapping data from mixed deciduous woodland and from lowland arable field margins. According to the Adult Aggression Hypothesis, juveniles have a poor persistence rate early in the breeding season as a result of aggressive behaviour shown by the adults. As the breeding season progresses, a drop in adult aggression levels results in increased juvenile persistence, which, in turn, leads to increased densities. The Habitat Saturation Hypothesis proposes that juveniles disperse from their parents' territories until the surrounding habitats are saturated and that this gradual saturation results in increased densities as the breeding season progresses. The observed correlations between adult and juvenile densities both in woodland and on field margins were consistent with the predictions of the Habitat Saturation Hypothesis.