Hippopotamus

A single herd of hippos may include up to 100 animals. The herd's location, foraging, and movement are A hippopotamus. Photograph by William & Marcia Levy. The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. controlled by a group of mature females. The females and their young inhabit the center of a herd's territory, called the crèche. The male's individual territories, called refuges, are spaced around the crèche. A bull will defend his territory against another bull. If roars and open mouths do not scare off the challenger, they attack each other with open mouths, trying to stab their canine teeth into each other's head or heart.

The animals breed as the dry season is ending, with the females selecting their mates. Hippos mate in water. Gestation lasts about eight months, and the calves are occasionally born in the water at the height of the rainy season when the most grass is available. A new calf is about 3 ft (1 m) long and weighs about 60 lb (27 kg) when born. On land, it can stand very quickly. It will be several weeks, however, before the mother and her infant rejoin the group.

Once taken into the crèche, the young hippos are tended by all the females. Although adult hippos have few enemies, the calves are small enough to be taken by lions and crocodiles. Until young hippos start to swim by themselves, the young may ride on their mothers' backs when in the water. Once they can swim, the calves may nurse, eat, and even nap under water. They automatically come up to the surface to breathe every few minutes.

Young females are sexually mature at three to four years old, but usually do not mate until they are seven or eight years old. Male hippos are mature at about five years old, but do not successfully challenge the dominant males for the right to mate until they are much older. A cow with a young calf will usually have another calf when the first one is two or three years old. Because an adolescent hippo is not ready to go out on its own until about four years of age, a cow may be taking care of two calves at once. In the wild, hippos live for about 30 years, while in captivity they can live past 40 years old.