Monks Wood, a deciduous wood of 155 hectares on clay soil, has an estimated population of 400 moles. There is an anastomosing system of permanent burrows, and when a mole is trapped its area of burrow is soon occupied by another animal. Little new digging occurs, except in winter, after frost has driven the soil fauna deeper into the ground. The burrows usually act as pit-fall traps for the food. Young animals migrating in summer may live more superficially, in tunnels in moss and grass, but survivers usually move into a permanent tunnel system by autumn.
Woodwalton Fen has an easily worked peat soil, and few earthworms. Here moles burrow at all seasons, presumably needing an extensive burrow system to catch sufficient food. In times of flood, the moles leave submerging ground but return very soon after the water subsides. They probably swim across flooded areas but iis yet we do not know if the same animals return after floods to the same burrows.
Moles are not good indicators of soil fertility, particularly as many mole heaps are made by few moles in poor soil, and fewmew heaps may appear in good soil with permanent burrows. We do not understand why there are so few moles in some apparently suitable pasture, with high worm populations, or how others manage to obtain sutficient food in infertile areas.