Effects of sheep grazing on abundance and predators of field vole (Microtus agrestis) in upland Britain

A technique using fresh feeding signs as an index of density was validated and used to survey the effects of sheep grazing on vole population densities in four upland habitats in the northern Peak District National Park, UK. In grazed areas Molinia caerulea grasslands supported most voles, Nardus stricta grasslands supported fewer and Eriophorum vaginatum and Calluna vulgaris-dominated areas supported least. There were highly significant negative relationships between vole sign density and sheep numbers in these habitats. Where sheep were excluded, these same habitats had between three and nine times higher sign densities, corresponding to between 1.5 and 2.5 times greater field vole densities. Population estimates of voles and predators such as short-eared owl approximately doubled under reduced grazing. Reducing sheep numbers in upland areas may therefore be critical in encouraging the recovery of predatory birds in the uplands.