Factors associated with the colonization of agricultural areas by common voles Microtus arvalis in NW Spain

Abstract

The common vole, considered a rodent pest when overabundant in agricultural areas, was traditionally absent from the agricultural plains of Castilla-y-León, NW Spain. However, it rapidly invaded ca. 50.000 km2 of agricultural land, where regular outbreaks have caused crop damages and conflict with farmers. To better understand the factors that triggered this massive invasion of previously unoccupied habitats, we studied the associations between the common vole range expansion and changes in climate and land uses in the region since the 1970s. We found long-term trends in climate, with some changes that could have helped the range expansion (increased fall precipitation and winter temperature) and other changes that may have impaired it (reduced summer precipitation and increased summer temperatures). Dramatic changes in land use also took place prior to and during the invasion period (marked increases in irrigated and green herbaceous crops such as alfalfa, which are preferred habitats for voles). We found strong associations between changes in vole distribution and the extent of green crops (irrigated crops and alfalfa) at regional level. The colonization probability of a given agrarian county increased with the extent of green crops, particularly so when vole presence in neighbouring counties was lower, and tended to decrease with increasing livestock abundance. Land use changes, especially increases in irrigated crops and alfalfa, appear to be amongst the main drivers behind the vole range expansion. We discuss these findings in relation to the social conflicts and management challenges that arose from the recent invasion of agricultural areas by crop-damaging common voles.