banks. They construct these tunnels and nests just below the roots of the vegetation (about 4–6 cm below ground) during the breeding season (June through late September). Females give birth and care for her young in these underground nests, lined with leaves and grass. Social life and breeding habits Water voles are usually found within 5 to 10 m from waterways. They form a polygynous social group, in which females tend to stay within their territory, which does not overlap other females, and males travel between burrows to reproduce with several females. Because of this system, males travel over a much larger home range than females, and they tend to be more aggressive than females, with aggressiveness coinciding with breeding patterns. Estrus is induced by contact with reproductively active males, and tends to first coincide with the appearance of vegetation in the spring. Both males and females have rather large flank glands, which serve to mark territories so that nests are not invaded by others, as well as signaling to mates during the breeding season. Water voles breed for 3 months during the summer, and young are born from June until late September. Females generally have litters of approx. 5-6 young, with a minimum gestation period of 22 days. Litter size tends to increase with age of the mother, and ranges from 2-10 young. Although water voles appear to have the ability to reproduce in large numbers, as do many other rodents, their population densities are actually kept very low and live in colonies of 8-40 individuals. This may be due to the very short breeding season compared to other rodents who breed for 6 months or more. Birthing and parental care Newborn voles are naked and blind, and weigh about 5 g. They are able to vocalize immediately, and within 3 days start to show fur. By day 10 they are running and climbing, and by day 17 they are swimming on their own. Mother feeds them by lactation until they are 21 days old, and they nest together for approximately 32 days, during which time the pups are growing about 1.24 grams per day. Evidence shows that although they may still be nesting with their mother, she provides very minimal parental care after weaning. Around the time they reach 40 days of age, they move to their own nests and about 3 weeks later reach sexual maturity. Approximately