Wood mice (Apodemus sylvaticus L.) as pioneers of recolonization in a reclaimed area.

A population of wood mice, Apodemus sylvaticus, was studied by live-trapping for 15 months in an area recently reclaimed from lignite open-mining, where the species is a pioneer of recolonization. Population dynamics, spacing behaviour and feeding habits were compared with data in the literature in order to investigate how these characteristics were affected by the peculiar habitat conditions and the special situation of early colonization. Population density was remarkably high with a peak of 86 individuals/ha in autumn and a low of 20 individuals/ha in late spring. The sex-ratio was always biased towards males except during periods of low density, when the ratio was close to unity. Individual body weights and the annual course of weight class distribution showed no distinct peculiarities, although body weight increased relatively slowly in late winter. Low juvenile survival, relatively low litter sizes and early termination of breeding were special features of the population. Furthermore, very few juveniles matured in the year of birth, and the best winter survival was found in mice born in the middle of the breeding season. Activity ranges were small compared with those given in the literature, and space use was similar in both sexes. As a direct effect of the habitat conditions, the diet was largely dominated by weed seeds. The possible reasons for and causal relations of these features are discussed.