The effect of fluctuating vole numbers (Microtus agrestis) on a population of weasels (Mustela nivalis) on farmland.

Abstract

1. Numbers of voles, weasels and the diet and reproductive performance of the weasel population were measured on a large area (25 km²) of farmland in the south of England.
2. Vole numbers showed a 4-year cycle of abundance during the course of the study and most populations were in phase. Peak populations were fourteen times the density of low populations.
3. Weasel numbers varied annually and peak numbers were over twice the minimum number. Relative changes in weasel numbers lagged behind changes in vole numbers.
4. Female weasels failed to breed during the year of lowest vole numbers.
5. The diet of male weasels showed distinct seasonal changes; females showed less seasonal variation than males. The difference is attributed to large differences in home range size between the sexes.
6. The proportion of voles in the diet increased with increasing vole density and was 16% in the lowest years and 54% in the highest.
7. When vole numbers were low birds were the main alternate food for weasels.
8. Changes in vole numbers were negatively related to previous changes in weasel numbers.
9. Changes in vole numbers were negatively related to the vole consumption by the weasel population the preceding year.