A team at the Royal Veterinary College, University of London, conducted an in-depth study of how hippos run—and the results surprised the researchers. These hefty, wingless mammals can sometimes lift all four feet off the ground and become completely airborne. That brief flight is hard to see with the naked eye. Hippos, or hippopotamuses (Hippopotamus amphibius), are among the largest land mammals, often weighing more than two tons, with adult males sometimes reaching up to four tons. Because hippos spend a lot of time in water, little has been known about how they move on land.
Hippos are airborne for longer than you might expect. By analyzing video footage of 169 movement cycles from 32 hippos, the researchers found the animals can be in the air for up to 15 percent of a movement cycle—a repeating pattern of steps—which works out to about 0.3 seconds. Some other animals, like horses, also have brief flight phases at speed, but that trait is unusual for very large mammals. For instance, elephants never lift all four feet off the ground at once.
The team also found that hippos predominantly trot whether they are moving slowly or quickly. That consistency is unusual among land animals. For example, rhinos and horses use a standard walking gait and switch to a trot or gallop as they speed up.
Studying hippos has been difficult partly because they’re dangerous and spend most of their time in water, so researchers haven’t had many safe opportunities to observe them on land, says Professor John Hutchinson, an expert in evolutionary biomechanics and the study’s lead author. To get around that problem, the team analyzed video recordings of hippos taken at the Flamingo Land Resort in Yorkshire.
The findings expand what scientists know about the capabilities of large land mammals and will help explain aspects of hippo evolution. Practically, the data can help veterinarians diagnose and treat hippo injuries more accurately. “We are thrilled to present the first study entirely dedicated to understanding how hippos walk and run,” Hutchinson said. “We were pleasantly surprised to see how hippos lift off the ground when they move quickly. It’s truly impressive!” The results were published in the journal PeerJ.
