In 1872, Leland Stanford, founder of California’s Stanford University, hired an eccentric inventor named Eadweard Muybridge to help solve a supposed (but undocumented) bet: the feet of a horse moving on all fours would leave the ground. or not?
Muybridge was a skilled photographer and managed to get blurry pictures of an “aerial” horse in mid-gait – an example of how the unaided eye alone cannot capture swift and subtle movements. He went on, along with others, to create what became cinematography. He also continued to capture images of many moving animals, attempting to capture them in mid-air. Of another large animal, the hippopotamus (which he did not photograph) Muybridge wrote:
On dry land its swiftest gait could hardly be different from the amble [meaning fast but still four-beat, lateral sequence]; perhaps a trot, but with a short, if any, period of non-support.
was he right As a scientist whose research partly focuses on how giant land animals like rhinos, elephants and giraffes move and how gravity uniquely limits how athletic they can be on land, I’ve long wondered how hippos move. on the ground.
Most people probably think of hippos in terms of their activities in the water, where they spend much of their time. But they are amphibious animals that spend about a third of their time on land. Giant in size (usually around 1,400 kg) similar to that of young elephants, hippos must be heavy and slow on land, especially since they also have to adapt to life in water and look so bulky. But what seems possible and what is true are not always the same. This is where science comes in, to address questions with evidence. We know that hippos don’t fly; they have no wings and are very large; but what can they really achieve under the heavy pull of gravity?
In a recent study, we showed that hippos do move – but at high speeds they can fly through the air on all fours off the ground at once. This is remarkable because we now know that hippos are one of the largest animals that can still fly through the air at great speeds and yet have also adapted to a semi-aquatic lifestyle.
A simple experiment
In studying the existing literature on hippo locomotion, I found that it was not clear what range of gaits or leg sequences hippos used.
Some studies said they used a “lateral sequence” gait pattern—a “four-beat” gait, contacting the ground with the left rear, then the left front, then the right rear, then the feet. front right.
Others said that the hippos only used a “tapping” pattern even at slower speeds. Here movement does not mean moving at a moderate speed like jogging. In the scientific analysis of movement, as in other fields such as equestrian sports, a trot is a “two-beat” gait in which the diagonal limbs move almost in unison, with the left, rear, and right forelegs contacting the earth, followed by the right. front back and left legs move away about half of the leg cycle (“space”).
Few scientific studies have considered what hippos do when they move quickly on land. There were some observations that, at least at moderate speeds, hippos moved.
So I designed a very simple experiment, analogous to what Muybridge did, but a common activity today: taking digital videos of hippos moving at a variety of speeds.
I sent my undergraduate veterinary student, Emily Pringle, to Flamingo Land Resort in North Yorkshire in the UK, armed with basic GoPro cameras, to capture video of their two adult hippos.
She noted during the two days of intermittent filming that the hippos were slow; just walking. It wasn’t a surprise. Not only did the hippos not spend much time on the ground (and were out of sight in their barn at night), but there was no way to motivate them to move quickly – they live a safe life.
There was a second part to our plan. The Internet is full of wildlife videos, so we searched YouTube and other websites for more videos of hippos moving at a variety of speeds on land to “increase” our data sample. This helped put our video of two zoo hippos in a larger context. We hoped to find some footage of hippos moving as fast as they could, in more motivated (perhaps wild) conditions.
We did.
Video testimony
We collected 169 steps from 46 video clips of 32 hippos. Most of it was slow walking, but all of these walking steps involved walking patterns. It is clear that hippos prefer to walk rather than use a four-beat lateral sequence pattern, even at slow speeds.
Videos of wild African hippos and a couple from zoos contained the most exciting find.
About 14 of our 46 videos of hippos showed at least brief periods of “unsupport,” as Muybridge called it—being airborne on all fours off the ground.
Victoria Wallace, Director, ZikomosafariCC BY
The fastest sequences showed the hippos flying through the air for about 0.3 seconds. That might seem really short, but it’s longer than a single foot can be on the ground (a little over 0.2 seconds). Furthermore, the nervous system of a large animal like a hippopotamus would involve long delays in response to an obstacle, so those aerial periods could be dangerous.
Our findings highlight how strange hippos’ movement is on land. Unlike most other mammals, especially larger ones, they just move, from slow to fast speed. We weren’t able to measure exactly how fast hippos can move, but I assume they’re probably not much faster than elephants, which I’ve previously shown move up to 25 km/h (with a sequence lateral “amble”, never in the air).
Their ability to fly even briefly through the air means that hippos are relatively more athletic than elephants, but still less athletic than white rhinos, which can be as large as a hippopotamus but can gallop and thus to be in the air, and perhaps faster than hippos. This variety of locomotion, extended by other very large animals I’ve studied, such as giraffes and even extinct dinosaurs, shows two general patterns.
First, even at giant sizes over 1000 kg, there are still a variety of athletic abilities that can be useful, such as moving faster than a slow walk, or even hovering.
However, secondly, at such proportions, there is inevitably a drop in top speed. As size increases, sooner or later certain athletic skills, such as being in the air, must be sacrificed, in exchange for the many benefits of gigantic size.