There are two species of hippos — the large/common hippo and the smaller relative, the pygmy hippo. Hippos are the third-largest living land mammal, after elephants and white rhinos. Despite their large and bulky appearance, they have adaptations to their semi-aquatic environments allowing them to move swiftly on both water and land. Their feet have four-webbed toes that splay out to distribute weight evenly and therefore adequately support them on land, and their short legs provide powerful propulsion through the water. The pygmy hippos digits are more spread out and have less webbing and, proportionally, their legs are longer relative to its body size. They both have skin tones of purple-grey or slate color, with brownish-pink coloring around their eyes and ears. They have very thick skin that is virtually hairless except for the thick bristle-like hair on their heads and tails. The outer layers of skin are quite thin, making them prone to wounds from fighting. Their flat, paddle-like tail is used to spread excrement, which marks territory borders and indicates status of an individual. Their powerful jaws are capable of opening up to 150 degrees revealing their enormous incisors.
Unlike us, the hippopotamus does not have sweat or sebaceous glands. Both species rely on water or mud to keep cool — this accounts for the amount of time they spend in the water. Instead of sweating, they secrete a viscous red fluid, which protects the animal’s skin against the sun and possibly acts as healing agents.
Their social structures are dependent on food and water conditions. These animals have a flexible social system. Common hippos are usually found in mixed groups of anywhere from 20 to 100 individuals held by a territorial bull, but in periods of drought large numbers are forced to congregate near limited pools of water. This overcrowding disrupts the hierarchical system, resulting in even higher levels of aggression, with the oldest and strongest males asserting dominance. Old scars and fresh, deep wounds are signs of daily fights. Unlike their social cousins, pygmy hippos are solitary and aren’t territorial. If they encounter each other outside of mating, then they simply ignore each other.
The surprisingly agile hippo climbs steep banks each night to graze on grass. They leave the water pool at night to graze for four to five hours, covering up to eight kilometers (five miles) of territory. They will eat about 40 kilograms (88 pounds) of food during this time. Their modest appetite is due to its sedentary life, which does not require high outputs of energy. When returning from grazing before dawn, they will enter their water pool at the same time.
