Abstract
The water vole naturally occurs at low densities throughout most of eastern France. However, densities can reach 500 voles/ha during the species' periodic outbreaks (which occur about every 6 years); these high densities lead to considerable damage, particularly to grasslands. Also, because chemical pesticides are used to control vole populations, outbreaks can have a negative, indirect impact on local fauna, and thus ultimately harm the net income of farms and disrupt the natural balance of agroecosystems. Water vole outbreaks were studied in Franche-Comte and Auvergne. They were found to be caused by multiple factors, including the proportion of the landscape dedicated to agriculture, the proportion of land under permament grass, and landscape heterogeneity. The increasing degree of specialisation taking place in livestock-producing regions over the last few years has promoted water vole outbreaks, whose breadth and intensity vary across regions.