Large-scale range expansion and eruption of common vole (Microtus arvalis) outbreaks in agricultural plains of NW Spain: historical reconstruction and novel impacts

By the end of last century the distribution range of Microtus arvalis in NW Spain greatly expanded and outbreaks began to be reported in recently-colonised agricultural habitats. Ever since, novel impacts to regional farming, biodiversity conservation and public health have recurrently been associated to vole outbreaks. Here we present the first attempt to reconstruct recent changes of common vole dynamics and distribution in the NW of the Iberian Peninsula. We compile published information for the last 50 years and describe a new methodological approach based on semi-quantitative data obtained from complementary sources. Our results show how, from late-1970s, the entire lowland plains of Castilla y León region were rapidly (< 20 years) filled in by expanding populations. Analyses of outbreaks also suggest a 5-year cyclic pattern from late-1970s onwards, contrasting with the typical 3-year cycle described in most populations of this species. Our results contribute to improve the current knowledge of rodent dynamics in Europe and may serve as a baseline to local pest management programmes.