Hippos spend their days soaking in lakes and riverbeds. They also travel by walking along the bottom of various bodies of water, and even sleep beneath the water.
But as mammals, how is it possible for them to breathe while beneath the water?
Hippos can’t breathe underwater because they’re mammals. Instead, they can hold their breaths for over five minutes at a time. They also naturally rise to the surface to breathe while sleeping before sinking back down. Even though they can’t breathe underwater, hippos’ bodies have many advantages from being in the water.
Hippos Can’t Breathe Underwater
If hippos spend so much time in the water and walking underneath it, how do they breathe? A hippo can’t breathe underwater; they have to breathe while still above the water’s surface.
Hippos often appear to be floating in the water. Just the barest amount of their heads and their backs may be visible.
However, these hippos aren’t floating. Just as they’re too heavy to swim, they’re too heavy to float, too. They’re actually standing in shallow water, which allows them to keep their nostrils above water to breathe.
A hippo can hold its breath for over five minutes, though, while its whole body is underwater. Their nostrils close to keep water out. They can also sleep underwater, though they’re still not breathing below the surface.
They have a natural reflex that activates while they’re sleeping. It allows them to push themselves to the surface, breathe, and then go back under, all without waking themselves up.
Hippos Are Semiaquatic Mammals
An amphibian, such as a frog or a newt, is a cold-blooded vertebrate. They are their own taxonomic class, whereas a hippopotamus belongs to the Mammalia class. Mammals can’t breathe underwater, and most are warm-blooded.
However, a hippo has an amphibious, or semiaquatic, nature. They spend a large portion of their day in or near water.
One reason for this is that they lack true sweat glands as we understand them. If hippos stay out of the water too long, they can dehydrate.
Hippos do secrete “blood sweat,” a red, thick substance that appears similar to blood. In reality, this is a layer of mucous that acts as a sunscreen and helps keep their skin moist.
It may also serve as protection against infections. Hippos don’t seem to suffer from wound infections even in dirty water.
Despite spending so much time in the water, hippos don’t swim. They are enormous animals, weighing up to 3,252 pounds (1,475 kg). Even the pygmy hippo species can weigh over 600 pounds (273 kg).
They also have very dense bones, weighing them down even more.
These characteristics make hippos too heavy to swim. Instead, they “bottom-walk” by pushing themselves off the bottom of the rivers in which they live. Their gait underwater is similar to a bouncing gallop or trot.
Hippos do leave the water in order to graze, but often only at night when it’s cooler. Even though they’re such big animals, they don’t eat much. They graze for up to six hours to eat about one and a half percent of their body weight.
For the largest of cattle, two and a half percent of their body weight is more common. Hippos’ smaller consumption is because they’re so sedentary. They spend most of their days in the water, not moving much.
Hippo’s Other Advantages In Water
Even if they can’t breathe underwater, a hippo excels at semiaquatic life. Their eyes, ears, and nose are all at the top of their heads. This allows them to submerge almost completely while still being able to use their senses.
When they do go underwater, their ears close just like their noses. The ears fold into a recess in their head to keep out the water. They can hear very well underwater as well due to the structure of their jaws and ear tissues.
Hippos also have four functional toes that splay wide and have a slight web between them. This helps them stabilize themselves in the water.
Hippos can’t breathe underwater because they’re mammals. They have to get their oxygen from the air. Even so, hippos spend a large portion of their time in the water.
Their bodies are well-suited for a semiaquatic life. Everything from their nostril placement, their toes, and their hearing helps them thrive in water. Water also helps them counteract their weaknesses on land.
Water helps hippos travel, stay cool, and conserve energy. Just because they can’t breathe underwater, doesn’t mean they’re at a disadvantage in it.