Hippopotamuses (hippopotami is also accepted as a plural form by the OED), also called Hippos, are gregarious, living in groups of up to 20 animals. They spend most of the day up to their nostrils in the waters of tropical rivers, as their skin transpires much more moisture than most animals and they are extremely susceptible to sunburn. They can close their nostrils and remain completely submerged for more than ten minutes. They are buoyant and very skilled and graceful in water. They feed on land mostly at night, consuming as much as 50 kg (approximately 120 pounds) of vegetation a day.
Despite the popular image of the animal being easygoing and peaceful, the Hippopotamus is actually one of the most dangerous African animals, said to account for more deaths than any other. Its canine teeth are 50 cm (20 inches) long, and it uses its head as a battering ram. The animals stand 1.5 metres tall (5 feet) at the shoulder and weigh between 2700 and 4500 kilos (roughly 3 to 4 tons). They are approximately the same size as the Black Rhinoceros; one or the other is the second-largest land animal.