Running elephants keep their feet on the ground
Elephants moving at full speed are actually running, even though they may not appear to be at first glance, U.S. researchers have confirmed.
Dr John Hutchinson from Stanford University, California and colleagues reached their conclusions by examining video footage of 42 adult elephants in Thailand. Their work is published in the current issue of Nature.
Elephants are unusual, write the researchers, in that unlike with other animals, it is not easy to tell whether they are walking or running. No matter how fast they go, elephants never have all four feet off the ground at the same time, which is the most easily identifiable hallmark of running.
For this reason, researchers have previously thought elephants to be capable of walking, ambling or trotting only, but not running. However Hutchinson and colleagues performed more complex analyses of the movement of elephants to determine that they do in fact run.
In a total of 188 trials, the researchers observed Asian elephants, Elephas Maximus in peak health moving at top speed along a 30 m long track in Thailand. The researchers used non-toxic paint to mark the elephants over their limb joints then filmed the animals. Later they were able to use the paint marks as a basis for digitisation of the animal's movement.
In general the elephants maintained an even speed over the track. Thirty two animals reached top speeds of over 4 metres per second. Of these, 20 went faster than 5 m/sec and three reached speeds of up to 6.8 m/sec (25 kilometres per hour). Previous estimates of top elephant speed had been about 15 kph although anecdotal evidence claimed they could reach 40 kph.
Looking at the pattern of feet falling on the ground is only one method of defining whether an animal is running. The researchers used two other methods to find that some aspects of the elephants gait appeared to fit technical definitions of running.
The researchers first used a method based on kinetics. This involves measuring the amount of time a given foot is in contact with the ground as a fraction of the time it takes for one complete set of four steps to occur. If a foot is on the ground less than half of the time it takes for a complete sequence of footfalls, it meets what is known as the "kinematic" definition of running. Hutchinson and colleagues found the fast moving elephants met this definition.
Another method of identifying running is based on biomechanics. This defines running as a bouncing gait in which the limb actually compresses and bounces back with a spring. The researchers found also that an elephant's centre of mass appeared to bounce at high speeds. If that turns out to be true, it means their gait also meets the biomechanical definition of running.
The researchers also report that Asian elephants - which can weigh more than 3 tons - seemed to bend their limbs slightly in order to move their bodies more smoothly. This research may provide insight into the biomechanical tricks that help large animals such as extinct dinosaurs and even people, overcome the physical forces that restrict their motion.