Diet and habitat selection of the pine marten in relation to competition with the red foxUse STORCH, Erik LINDSTROM and Jonas de JOUNGE Storch I.. Lindstrom E. and de Jounge J. 1990. Diet and habitat selection of the pine marten in relation to competition with the red fox. Acta theriol. 35: 311 -320.After a reduction in red fox Vulpes vulpes Linnaeus, 1758 density in south-central Sweden due to an epizootic of sarcoptic mange, which reached the study area in 1982, pine martens Martes martes Linnaeus. 1758 became more abundant. By scat analysis and by snow-tracking we compared winter diet and habitat selection of martens before (1979-80) and after (1987) the decline in foxes to test potential effects of relieved competition on martens. We also used radiotelemetry to study habitat selection after the fox decline in winter and in summer. We were able to show that, at least in the winter situation, martens and foxes do not compete over field voles Microtus agrestis which are a favoured prey of foxes. Probably snow conditions rather than competition limited the consumption of voles by martens in winter. The avoidance of clearcuts by martens seemed to be related to the martens' escape behaviour and had not changed after the decline in foxes. Our data did not contradict relieved interferenceand resource-competition as causes of the increase in the marten population. Our study confirmed the role of the pine marten in the boreal forest as an opportunistic generalist predator which is largely bound to old successional stages.