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First published online September 19, 2006
Journal of Experimental Biology 209, i (2006)
Copyright © 2006 The Company of Biologists Limited
doi: 10.1242/jeb.02515
Inside JEB |
ARE HIGH-SPEED ELEPHANTS RUNNING OR WALKING?
kathryn{at}biologists.com
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John Hutchinson is intrigued by the way big animals move; crocodiles, elephants, even extinct mammoths fascinate him. So when Hutchinson met Rodger Kram in Berkeley, he recognised a kindred sprit to discuss big animal biomechanics with. One question that puzzled Hutchinson was how baby elephants move; massive adults never run, but Hutchinson wondered whether smaller, calf sized, youngsters could. Curious to find out what was known about elephant locomotion, the pair turned to the literature, but soon found it littered with confusion and anecdotes. Hutchinson realised that before he could satisfy his curiosity about the youngsters, he'd have to clear up the confusion and collect some reliable data on the adults (p. 3812).
Filming captive African elephants at local zoos in the USA, Hutchinson began analysing their movements over a range of speeds. But the animals never went faster than a leisurely 4 m s-1, always proceeding with a pendulum like gait reminiscent of walking. Hutchinson soon became suspicious that the couch-potato captives might not be capable of reaching the speeds that fit and active elephants reach routinely. He began contacting elephant experts around the globe in search of fitter animals, and realised that he'd probably found the ideal elephants when Richard Lair sent him stopwatch times recorded at elephant races in Thailand; the Asian elephants were moving at speeds approaching 7 m s-1. Hutchinson converted the speeds into the dimensionless Froude number, often used as an indicator of walking or running gaits, and realised that it was well above the transition value of 1 (where walking gaits switch to a bouncing run) at the animals' top speeds. Were these elephants running? Hutchinson needed more evidence about the animal's unorthodox running style to decide, so headed to Thailand.
Arriving in Lampang, Hutchinson and Dan Famini filmed 42 animals, ranging in size from 600 kg youngsters to 3000 kg adults, as they hurtled along accompanied by their trainers. He remembers that it was clear on the first day that these animals were outpacing the captive zoo animals and says `we knew right then we would get the data we wanted'.
After weeks of filming, the pair returned to the USA to begin laboriously analysing each `run', frame by frame. Recording each animal's footfall pattern and hip and shoulder movements, Hutchinson combined his observations with African elephant data from Robert Dale in Indiana and Delf Schwerda and Martin Fischer in Germany, and compared the African and Asian animals' gaits to see whether the animals were walking or running. Sure enough, at speeds below about 4 m s-1, both the species seemed to use a pendulum-like walking gait and there was virtually no difference between the African and Asian elephants' movements.
But what happened as the Asian animals moved up a gear and passed the gait-transition Froude number of 1? Were they running or walking? Scrutinising the animals' footfall patterns, the team noticed subtle changes. The animals' rear legs appeared to begin `running' as they became bouncier and both feet became airborne simultaneously. Meanwhile the front legs remained relatively rigid, despite becoming simultaneously airborne too. However, the rear and front legs never become airborne at the same instant. All of the elephants always kept at least one foot in contact with the ground, even at a record-breaking 6.8 m s-1 top speed. Considering the speed and motions, Hutchinson and colleagues suspect that the animals were using their limbs like bouncy pogo sticks; just like runners. The animals were effectively running, even though they never left the ground.
And how did the babies, which had set Hutchinson off on this odyssey, compare with their elders? Their running style was just a scaled down version of the adults. Hutchinson isn't sure why the youngsters fail to trot or gallop; `it would certainly be an advantage to them escaping predators' he explains, but suspects that the elephant's curious running style is hardwired from an early age.
References
Hutchinson, J. R., Schwerda, D., Famini, D. J., Dale, R.,
Fischer, M. S. and Kram, R. (2006). The locomotor kinematics
of Asian and African elephants: changes with speed and size. J.
Exp. Biol. 209,3812
-3827.
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