Hippopotamuses are large, semi-aquatic mammals uniquely adapted to a life spent largely in water. Though their name, derived from Greek, means “river horse,” they are more closely related to pigs, whales, and dolphins. These robust creatures inhabit the rivers and lakes of sub-Saharan Africa, showcasing remarkable abilities that allow them to thrive in their watery environments.
How Long Hippos Stay Submerged
Adult hippos typically hold their breath for about three to five minutes when submerged. While five minutes is common, some individuals can remain underwater for five minutes or even longer, with observations noting durations up to six minutes. Newborn hippos, however, possess a more limited capacity, only able to hold their breath for approximately 40 to 60 seconds at a time.
Physiological Features for Underwater Life
The remarkable breath-holding ability of hippos stems from several specialized physiological adaptations. Their nostrils and ears are positioned high on their heads, allowing them to remain above the surface for breathing, seeing, and hearing even when most of their body is submerged. When fully diving, these openings close tightly to prevent water entry. Hippos possess an automatic breathing reflex, enabling them to surface for air without conscious effort, even while sleeping underwater; they simply bob up, take a breath, and sink back down.
Hippos also have unusually dense bones, particularly in their legs, which act like natural weights, helping them sink and walk along the riverbed rather than floating. This bone density, combined with their large lung capacity and efficient oxygen utilization, contributes to their prolonged submergence. Their muscles contain a high concentration of myoglobin, a protein that stores oxygen, enhancing their underwater endurance. When submerged, their heart rate can slow, and blood flow is redistributed to vital organs, conserving oxygen and extending time beneath the surface.
Underwater Activities and Lifestyle
Hippos spend up to 16 to 18 hours each day submerged in water, which is central to their lifestyle. Despite their aquatic nature, they do not swim in the traditional sense; instead, their dense bodies allow them to walk, trot, or gallop along the bottom of rivers and lakes, sometimes pushing off the riverbed to move with surprising agility. This method of locomotion enables them to navigate their watery homes effectively, reaching speeds of up to 8 kilometers per hour underwater.
Spending most of their day in water helps hippos regulate their body temperature and protects their sensitive skin from the intense African sun, as their skin can dehydrate quickly if exposed for too long. They engage in various social behaviors underwater, including resting, interacting within their groups (known as schools or bloats), and even giving birth. While they live in water during the day, hippos emerge at night to graze on land, consuming significant amounts of grass over several hours before returning to the water by dawn.