Evidence for different drivers behind long-term decline and depression of density in cyclic voles

Decline and long-term depression of mean densities of the grey-sided vole (Myodes rufocanus) and the field vole (Microtus agrestis) have occurred in managed forest landscapes of Sweden since the 1970s. Generally poor over-winter survival during a period with mild winters suggested a common climatic driver, but other explanations exist. Here we explore the response of the grey-sided vole, preferring forested habitats, and the field vole, preferring open habitats, to clear-cutting of old forest in Sweden. The cumulated impact from long-term clear-cutting explained local disappearances of the grey-sided vole. Maintained connectivity of old forest to stone fields was important for local population survival, since no such populations disappeared. For the grey-sided vole, it is probable that climate is not the dominating driver due to different timing of the decline in our study area. Instead, habitat loss is concluded as being a potential cause of the decline in mean density and depression of grey-sided vole densities. The long-lasting depression of field vole densities, despite favourable landscape changes, suggests action of another strong driver. A recent field vole recovery, essentially back to pre-decline densities and distribution, coincided with favourable winter/snow conditions, suggesting a climatic driver in this case.