An investigation of the population ecology of syntopic shrews inhabiting water-cress beds

The population ecology of the shrews Neomys fodiens, Sorex araneus and S. minutus living syntopically in an area of commercial water-cress beds was investigated by live-trapping over a two-year period. The shrew population comprised 52% 5. araneus , 31% N. fodiens and 17% S. minutus. Sorex araneus was the most numerous species in all seasons. Peak numbers of shrews occurred in summer with low numbers in the ensuing winter. Input of new individuals was high, especially of N. fodiens which exceeded 60% in most months. Survival in the study area never exceeded 8 months in N. fodiens and 11 months in S. araneus. Both species suffered approximately 50% mortality and emigration in the first two months of life. Apart from a few, more nomadic, shrews, N. fodiens and S. araneus seemed quite sedentary during trapping periods, moving a mean distance of 13.7 m and 17.2 m between successive captures, respectively. The relatively low numbers of recaptures of N. fodiens at successive trapping periods indicated nomadic behaviour. Both species were more active during darkness than during daylight, and were more active in spring and summer than in winter. High turnover of the shrew population was attributed to mortality and emigration. Emigration was possibly encouraged by competition for space, particularly for nesting sites.