Hippopotamuses: Hippopotamidae

Hippos do not feed in groups (with the exception of mother-offspring) because they are largely immune to predators and so are able to forage without fear of attack. Male hippos are in charge of home ranges, which they keep for four years in rivers and at least eight years in lakes. There have been reports of hippos retaining the same range for the entire span of their lives, twenty to thirty years. Herds average ten to fifteen in size, but vary from two to fifty. Nonbreeding males, though tolerated, are often the victims of territorial fights with breeding adult males. These "bachelor" males tend to live in herds of their own or alone.

Though large, hippos can run 18 miles per hour (30 kilometers per hour) when threatened, and they are able climbers. They are not able to jump and won't even attempt it.

Both hippo species mate and give birth in the water, but the pygmy hippo also mates and gives birth on land. Pregnancy lasts 227 to 240 days and results in the birth of a single calf. Calves nurse (drink mother's milk) underwater. Male hippos begin breeding between the ages of six and fourteen, whereas females are ready to breed between the ages of seven and fifteen. Calves are usually born in the rainy months.

Healthy adult hippos do not fall prey very often, but young hippos and old or sick hippos are in danger of being killed by lions, hyenas, and crocodiles.