The common hippopotamus is one of Africa’s most recognizable large mammals. Beyond being a fixture of the continent’s waterways, the hippo’s daily habits and unique biology actively shape both its aquatic and terrestrial environments. Understanding this species means looking beyond its size to appreciate its ecological significance.
The Dual-Habitat Lifestyle
The hippopotamus leads a semi-aquatic life, dividing its time between water and land. To protect its sensitive, largely hairless skin from the sun, it spends up to 16 hours a day submerged in rivers, lakes, and swamps. Lacking sweat glands, hippos depend on water or mud to stay cool and prevent their skin from drying out.
Several physical traits are tuned for this lifestyle. A hippo’s eyes, ears, and nostrils are positioned high on its head, allowing it to see, hear, and breathe while submerged. Their skin secretes a viscous, reddish fluid called “blood sweat,” which acts as a natural sunscreen and moisturizer with antiseptic properties. When underwater, their nostrils close automatically, and a clear membrane protects their eyes, enabling vision.
This dependence on water dictates their daily routine. The need for sun protection keeps them in aquatic habitats during the day. At night, they emerge onto land to feed, a pattern driven by the dual requirements of thermoregulation and food acquisition.
Foraging Behavior and Diet
As dusk falls, hippos leave the water to graze. They are nocturnal herbivores that venture onto land to consume large quantities of short grasses. Using their wide, muscular lips, they crop grasses close to the ground, creating distinct grazing areas called “hippo lawns.” These nightly excursions can cover up to five miles (8 km) from their water source.
An adult hippo consumes 80 to 110 pounds (40-50 kg) of vegetation each night. Their diet consists almost entirely of terrestrial grasses, as they consume very few water plants despite their aquatic lifestyle. While fruits may supplement their diet, grasses form the bulk of their food intake.
Role as Ecosystem Engineers
The hippopotamus is an ecosystem engineer, a species that modifies its environment. Their dual-habitat lifestyle creates a link between terrestrial and aquatic systems. By consuming grass on land and spending their days in the water, they facilitate a massive transfer of nutrients across these ecosystem boundaries.
The primary impact comes from depositing dung into rivers and pools. After consuming large amounts of grass, hippos excrete nutrient-rich waste into the water. This dung, loaded with nitrogen and phosphorus, acts as a fertilizer that stimulates the growth of algae and microorganisms. This enrichment forms the base of the aquatic food web, supporting invertebrates and fish. In some river systems, the daily organic matter input from a large hippo population can be measured in thousands of kilograms.
Beyond nutrient cycling, hippos physically alter the landscape. Their repeated movements create defined paths through wetlands and on land, which can alter water flow and create new channels. This trampling and wallowing behavior can widen riverbanks and carve gullies, changing the habitat’s physical structure and benefiting other species by opening access to resources.
Social Structure and Interactions
Hippos are social animals living in groups called pods, which can range from a few individuals to over 100. A pod is composed of a dominant bull, multiple females, and their offspring. The dominant male defends a stretch of water, granting him breeding access to the females in his territory. This territorial behavior is enforced in the water but does not extend to their nocturnal grazing grounds.
The social hierarchy is most apparent among males, who engage in dominance battles. Subordinate bachelor males are tolerated within a territory if they remain submissive to the dominant bull. Females form strong bonds and cooperatively protect calves from danger, with mothers being particularly protective of their young.
Due to their size and aggression, adult hippos have few natural predators, though young or weak individuals can fall prey to lions, hyenas, and crocodiles. Hippos defend themselves with their powerful jaws, which are armed with long, sharp canine teeth. Their aggression is a survival trait in an environment with numerous large predators.
Conservation Status and Human Conflict
The common hippopotamus is listed as Vulnerable on the IUCN Red List. The main drivers of their population decline are habitat loss and unregulated hunting. Across Africa, the expansion of agriculture and diversion of water for farming has fragmented the wetlands and rivers that hippos depend on. This encroachment leads to increased human-wildlife conflict.
As their habitats disappear, hippos are forced into contact with human settlements, where they may raid crops for food. This causes economic damage and can lead to retaliatory killings. The conflict is worsened by drought and the confinement of hippo populations to smaller areas. Hippos are also poached for their meat and large canine teeth, which are a source of ivory.