Capybaras (Hydrochoerus hydrochaeris) are the largest rodents in the world. They live in herds of about 20 individuals, feeding by day on the banks of rivers and in swampy areas. Although they are well suited to being in water, with eyes and nostrils high on the head and webbed hind feet, capybaras do not feed for long periods in water. They tend to use water as a refuge from predators and as a means of keeping cool on hot days. If startled, capybaras gallop into water and may swim to the safety of floating plants. When they surface, only their eyes and nostrils are visible.
Capybaras do not have permanent dens, but sleep in waterside thickets. Each herd contains several adults of both sexes as well as their offspring, all conforming to a hierarchy. A single male leads the herd. Only he can mate with the females in the herd. Fights often break out between the other males as they attempt to improve their rank.