The mounds of earth are therefore flatter and irregular in their form. It is therefore easy to see whether the burrow system is inhabited by water voles, by opening the burrows. The rodents avoid an interruption of the burrow laterally and close the old burrow from both sides. Moles burrow beneath the spot which was interrupted and establish a new burrow underneath it. Agropyron repens, wild black salsify, sorrel, wild chervil, plantain, buttercups, yarrow or crocuses.
Common voles feed from green plant parts as well as cereals and seeds.
Under such conditions, the population density increases at almost regular intervals, which in some years is catastrophic. It is not uncommon in such years for the population density to exceed 1000 individuals per hectare meadow, and on the north west German coast for the common vole population density to reach 5000 individuals in extensive meadowland. Such population peaks occur in water voles once every 5 to 8 years, on average once every 6 years. A massive increase in the common vole population occurs once every 2 to 4 years. However, the population densities stated are not always so extreme.