The capybara spends much time in water and is an excellent swimmer and diver; it has partial webs between the digits of both its hind feet and forefeet. When swimming, only its eyes, ears, and nostrils show above the water. Capybaras feed on plant material, including aquatic plants, and their cheek teeth grow throughout life to counteract the wear and tear of chewing. They live in family groups and are active at dawn and dusk. In areas where they are frequently disturbed, capybaras may be nocturnal. Males and females look alike, but there is a scent gland on the nose that is larger in the male. They mate in spring, and a litter of 2 young is born after a gestation of 15 to 18 weeks. The young are well developed at birth.