Distribution, Territoriality and Numbers of the Weasel Mustela nivalis in Relation to Prey Abundance

Distribution and numbers were studied by capture-recapture. 319 captures were made, including 24 individual animals. Territoriality was examined by homing experiments, dominance tests, and removal. The distribution of weasels was uneven. Only two of the habitats examined were regularly exploited, viz. a spruce plantation and a replanted clearing. There was a seasonal change in distribution pattern. In late summer and autumn some adult male weasels maintained territories. In spring the males were roving, staying only for short periods in limited areas. Distribution and numbers were closely related to the abundance of small rodents. Reproduction was absent one year in one of the habitats, when rodents were scarse. A calculated minimum density necessary for successful breeding was not found. Prey density was decisive for territorial establishment. Individual qualities were important in territorial defence. Two adjacent males demonstrating equal status of dominance and maintained the same territories for several months. The size and changes of two other males' ranges corresponded to the dominant-subordinate status of the individuals. Some individuals failed to defend a territory.