Analysis shows hippos get all four feet off the ground simultaneously for up to 15% of the time when running at full speed
Apparently, hippos CAN fly. This is the conclusion reached by the authors of a study out of the University of London’s Royal Veterinary College, which discovered that when hippos move at full speed on land, all four of their feet are regularly in the air for brief moments.
The common hippopotamus, Hippopotamus amphibius, also known as the Nile hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. There are two species of hippos, the other being the pygmy hippo. Hippos are among the largest living land mammals, with adult males averaging 1,500 kg (3300 pounds) and females 1,300 kg (2866 pounds). For such a massive animal, they also move surprisingly fast — some reaching speeds of up to 30 km/hr (18.6 mph). (For reference, the average human’s running speed is around 13 kph, and even Usain Bolt could only very briefly reach 44.7 kph.)
But how, exactly, do hippos move — and so quickly? Some previous studies claim hippos use a standard quadrupedal walk, with a footfall sequence of left hind, left fore, right hind, right fore – similar to elephants. Other studies claim they trot with diagonal feet moving in synchrony. But prior research hasn’t identified whether hippos actually become airborne when they move quickly, as seen in many other mammals, such as horses, a feat that is much less common amongst larger animals.
This controversy raised a few questions: do hippos always trot, regardless of their speed, or does their gait include an aerial (suspended above ground) phase? How do their footfalls and stride parameters change with their changing speed?
Hippos are one of the most dangerous animals in the world to humans. They are famous for their bad tempers, and are known to attack when provoked (and often, even when not provoked) and to give chase whenever they feel the need to do so. Because hippos are so dangerous and unpredictable, a team of researchers based at the Royal Veterinary College led by John Hutchinson, Professor of Evolutionary Biomechanics, and veterinary student Emily Pringle, surveyed online videos of captive hippos living at Flamingo Land Resort. To achieve their goals of gathering and analyzing a sample of 169 strides from 32 hippos, Professor Hutchinson and Ms Pringle also filmed two zoo hippos moving quickly around their paddock.
“I’ve struggled to get any work done on hippos before because they’re so hard to access,” remarked Professor Hutchinson, whose research straddles the fields of evolutionary biology and biomechanics, with an emphasis on understanding how very large animals stand and move and how locomotion evolved in different groups of land vertebrates across major evolutionary transitions and transformations.
Why is this such a mystery?
“They’re incredibly dangerous, they tend to be most active at night, and they spend a lot of their time in the water.”
In contrast to elephants, which can only walk, and rhinos, which can walk, trot and gallop, Professor Hutchinson and Ms Pringle’s video analysis revealed that hippos moving at high speed are doing so by trotting. Even when moving at top speed, hippos still used trotting (or near-trotting) footfall patterns, but with one unusual twist: they actually do lift all four of their feet off the ground at the same time at certain points in their gait — which happens 15% of the time.
“We were pleasantly surprised to see how hippos get airborne when they move quickly,” Professor Hutchinson said in a statement. “It’s really impressive!”
This aerial phase during the fast trot was a new discovery that so far, is unique to hippos. Each aerial occurrence of ‘flying hippos’ was brief, lasting for approximately 0.3 seconds per stride. And yet, even after detailed analysis, Professor Hutchinson and Ms Pringle did not find that hippos could actually gallop or run, per se. Instead, they move at top speed by trotting (Figure 1, also video).
“Hippos are one of the very few four legged animals at all that just trot,” Professor Hutchinson noted. “That was a pretty neat finding.”
Professor Hutchinson and Ms Pringle also report that hippos move similarly through water. They cannot swim, but they can trot at high speed along the bottom of the bottom of a river.
The findings could help inform the way that hippos are kept in captivity, particularly by detecting and monitoring whether hippos are suffering physical issues.
Surprisingly, one video has surfaced that depicts a pygmy hippo that was actually galloping. This is providing Professor Hutchinson with a direction for future hippo research: can small hippos, such as baby hippos and baby pygmy hippos, gallop but lose this ability when they grow physically larger? Why?
Source:
John R. Hutchinson and Emily V. Pringle (2024). Footfall patterns and stride parameters of Common hippopotamus (Hippopotamus amphibius) on land, PeerJ 12:e17675 | doi:10.7717/peerj.17675
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