The burrow system of the common vole (M. arvalis, Rodentia) in Switzerland

Fifty burrow systems of Microtus arvalis were excavated, from October 2006 to August 2007 in wildflower fields and quasi-natural habitats in five areas near Bern, Switzerland. They comprise an aboveground part, which is longer in spring/summer, and a subterranean part, which is longer in autumn/winter. Three main construction types exist: (a) linear burrows, (b) compact and tight networks, and (c) structures containing both a compact network around the nest and linear parts elsewhere. The subterranean length was on average 16.9 m (range: 0.5-70.2 m) and aboveground length 39.4 m (range: 0-95 m). Numbers of intersections, dead ends, and openings correlate significantly with subterranean burrow length. Nests and food caches were located at a maximal depth and mostly in a central position, as revealed by graph theory.