The Fossorial Water Vole (Arvicola Scherman) In The Pyrenees, Factors Involved In Its Population Abundance

The Fossorial Water Vole (Arvicola scherman) is a species of great interest, both because of its role as prey for a wide variety of predators, and the damages on agriculture. The variation in its population abundance and the factors that modulate it have been widely studied in northern Europe, but they are rather unknown for Pyrenean populations. Here we show the results obtained in the monitoring plan for the species in Navarra from 2016 to 2020, describing both the inter- and intra-annual changes in population abundance, as well as the effect of environmental factors and agricultural management. We found intra-annual variation in its abundance, with significantly higher values in spring than in summer. Interannually, there was a significantly higher abundance both in 2016 and 2020. The accumulated rainfall in the three months prior to sampling and grazing with sheep were the two most important factors that explain variation in population abundance. Both factors had a positive effect on the Fossorial Water Vole, so that its abundance increased with wetter months before sampling and in areas where sheep were present. The role of these factors and other variables of landscape and agricultural management in the changes of abundance of this rodent are also discussed.