Hippos can run so fast they become airborne

I’ll believe that when pigs fly.

If you find it hard to imagine that a two-tonne creature with no wings could make itself airborne, you’re not alone. But a new study reveals that hippopotamuses (known less tongue-trippingly as hippos) sometimes run so fast that they become airborne.

Though amphibious, hippos are some of the biggest land animals – often weighing over 2,000kg (2.2 tonnes). As they spend a lot of time in water, we know less about how they move on land.

Turns out, they’re actually off land more than we thought. In fact, the researchers found they can become airborne for substantial periods of time: as much as 15 per cent of their stride cycle (their repetitive pattern of steps). That’s about 0.3 seconds.

Some other animals become airborne with speed, including horses (and some – very good – human runners). But it’s unusual in larger animals. Elephants never leave the ground with all four feet.

Existing research has been unsure about whether hippos’ stride cycles are more like those of elephants (which are quadrupedal, so their left legs move forward together and then the right), or like horses when they are trotting (diagonally, with the front leg synchronising with its opposite at the back).

But the new study by the Royal Veterinary College found that hippos almost exclusively trot, whether they’re slowly walking or running. It’s unusual for land animals to be so unvaried: rhinos and horses have a standard quadrupedal walk then trot or gallop as they gain speed.

The researchers say the results push what we know about the abilities of land mammals, and could help us learn about how hippos evolved. Practically, it could also help vets diagnose and monitor hippo injuries.