Hopping to survival

Press, Volume CXIV, Issue 33446, 30 January 1974, Page 14

Hopping to survival

(By

LONDON.

Kangaroos are still around because they can hop — that, at least, is one theory put forward by two zoologists who have been watching the antics of kangaroos made to run on a treadmill.

Hopping, it seems, is a very economical method of getting about. The proof lies in studies of two red kangaroos that were trained to hop on a treadmill while wearing a face mask. The treadmill measured their speed, while the face mask measured their oxygen consumption.

The idea for the experiments came when two zoologists working at Harvard University noticed that a hopping kangaroo looks a little like a bouncing ball or a bounding pogo stick. A lot of the energy used in each hop seems to be stored and used in the next one in the same way that a ball keeps bouncing when it is dropped. In the experiments the kangaroos were taught to hop on the treadmill for periods of up to 20 minutes at speeds of up to 22 kilometres an hour.

After a minute of hopping their oxygen consumption reached an almost constant level. If anything, it dropped slightly as the animal went faster.

In most animals (including man) oxygen consumption increases as speed increases because the oxygen is needed to break down sugar in the

body which keeps the muscles going.

The studies also show that kangaroos increase their speed by lengthening their hop. Neither the rate nor the height of hopping changes much over a wide variety of speeds. Extra speed is achieved simply by altering the angle of take-off. Drs Terence J. Dawson land C. Richard Taylor explain that discovery in terms of the nature of a kangaroo’s Achilles tendon, which is extremely long and thick: 35 centimetres long by 1.5 centimetres in diameter.

Once its hind legs are on the ground, the kangaroo lifts its bent feet and starts the cycle again. Drs Dawson and Taylor conclude that at speeds of up to about 18 kilometres an hour kangaroos expend more energy than a running fourlegged animal of the same weight. But above those speeds, because the kangaroo’s oxygen consumption does not increase with speed, it seems to be more economical to hop. All of that makes it difficult to understand why hopping is not more popular in the animal kingdom. Only Australia has large hopping animals, although, as Drs Dawson and Taylor say, “hopping appears to be an inexpensive way to travel at high speeds.” But while it may be strange that large hopping animals are limited to one continent, the economy that hopping allows may explain why kangaroos survived the advent of man in Australia while other marsupials became extinct.

Between 20,000 and 30,000 years ago there were marsupial lions and wolves and large four-footed herbivores, some of which were the size of a rhinoceros.

Only the hopping herbivores (kangaroos and wallabies) survived the arrival of man and his dog, the dingo. The reason, Dr Dawson and Dr Taylor speculate, may simply be that hopping away fast demanded less energy of the kangaroo than running away did of the other large marsupials.