Elephants run in slow motion
Unusual gait could reduce stress on the limbs of large animals.
Despite their cumbersome appearance, elephants can run. And, researchers have found, they break into that run at surprisingly slow speeds.
Elephants typically stroll along at a leisurely 4 kilometres per hour, explains John Hutchinson of the Royal Veterinary College in London. But once they ramp up to just twice this speed they start to use their back legs "like pogo sticks" to drive their bodies forward, bouncing over their relatively stiff, vaulting forelimbs. This unusual gait counts as running, says Hutchinson, whose study on elephant locomotion is published today in the Journal of the Royal Society Interface1.
Hutchinson studied the locomotion of five elephants in safari parks in the United Kingdom. Fitted with four motion sensors — two on their backs, two on their feet — the animals plodded, and in some cases dashed, along a 25-30-metre track, enticed by food rewards and the encouragement of their trainers. The fastest speed clocked up during the experiment was a modest 12.6 kilometres per hour, perhaps suggesting the elephants were a little out of shape.
Earlier work by Hutchinson's team in Thailand2 showed that more athletic individuals can reach speeds of up to 24 kilometres per hour, and provided some of the first evidence that elephants can indeed run (as opposed to just walking very quickly) — an issue that had previously been much disputed. But in that study they spotted a running gait only at speeds of more than 16 kilometres per hour.
"Our previous study looked at the top speed of elephants — we didn't really look at gait transition in any detail," says Hutchinson. "The mystery was always at what speed they changed gait."
Hutchinson says that he was surprised by the fact that elephants start running at the relatively slow pace of about 8 kilometres an hour — slower than a gentle human jog. But now he suspects that it is common for many large mammals, such as rhinos and horses, to change gait at a much lower speeds than their smaller relatives.
"We don't know why that is," says Hutchinson. "We can only speculate — but it could be for reasons of stability and to reduce the considerable stress on their bones and muscles."
In the past, scientists doubted whether elephants could be said to run at all — after all, they always keep at least one foot on the ground. However, the modern definition of running doesn't require an 'aerial phase', says Bill Sellers, a biomechanics expert at the University of Manchester, UK. "More and more scientists think that being airborne isn't necessary, and looking at locomotion in terms of energy transfer provides a more useful definition of running."
The modern definition envisages that an animal's legs act like a spring when running, and like a rigid pole when walking. "Imagine a bouncing ball compared to a walking toy soldier and you can see the difference," Hutchinson explains.
Much still remains to be learned about elephant locomotion, however. It is possible that elephants have more than just two gaits, says Hutchinson. "We are planning to carry out further tests with elephants at high speed. It is possible that they are doing something totally different that we have never seen before."
- Ren L. & Hutchinson J. R. J. R. Soc. Interface, doi:10.1098/rsif.2007.1095.
- Hutchinson J. R., Famini D., Lair R. & Dram R. Nature, 422 . 493 - 494 (2003).
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