A Marsupial With a Spring in Its Step

BY AWAKE! CORRESPONDENT IN AUSTRALIA

“EACH day when I came home from school, Joey, my pet kangaroo, would be sitting there waiting for me at the gate,” John recalls. “As soon as I opened the gate, he would jump up and embrace me with his forelimbs, and I would embrace him. We’d talk to each other in a language that said, ‘It’s great to see you!’ Then Joey would bound up the driveway a few yards like an excited dog, hop back, and repeat the process until we got to the house.”

People living in the Australian bush are legally permitted to have pet kangaroos, as John’s family did. Generally, these kangaroos are orphans, having been rescued as babies after their mothers were killed, perhaps when trying to cross a road. Even though it was the name John gave his pet, “joey” is, in fact, the common term for a baby kangaroo.

Naturally, the joey’s adopted family want to make it feel at home quickly. So one of the first things they do is give it a pouch. They choose a location away from the elements—and at a comfortable distance from the fireplace—and there they nail a large, tough cloth bag with a slot cut in it to resemble a mother kangaroo’s pouch.  Then they put the joey into it with a bottle of warm, specially prepared milk. In this way many joeys are helped to survive. They soon adapt to their new pouch, diving into it headfirst, as if it were their mother’s.

How Do You Describe a Kangaroo?

Animals that raise their young in a pouch, or marsupium, are called marsupials. Comprising some 260 species, marsupials include the kangaroo, koala, wombat, bandicoot, and opossum, the only species native to North America. Understandably, early explorers found these unusual animals, especially the kangaroo, difficult to describe to people back home. The first to put the word “kangaroo” into written English was British explorer Captain James Cook. He likened the animal to ‘a greyhound that jumps like a hare or a deer.’ When a live kangaroo was later exhibited in London, it caused a sensation.

Kangaroos have big ears that swivel about on a deerlike head. Their small but powerful forelimbs resemble human arms, especially when the kangaroo stands erect. Kangaroos also have large, muscular hips; a long, thick, sinuous tail; and, of course, huge feet—a characteristic that has earned them the designation “Macropodidae,” meaning “long feet.”

Some 55 species of Macropodidae range in size from that of a man down to that of a rat. All Macropodidae have short forelimbs and long hind limbs for hopping. Red kangaroos, gray kangaroos, and wallaroos, or euros, are the largest. One male red kangaroo measured over seven feet [200 cm] from his nose to the tip of his tail and weighed 170 pounds [77 kg]. Smaller species of kangaroo are called wallabies.

Have you ever seen or heard of a kangaroo that lives in trees? Well, believe it or not, kangaroos do have a “monkey” in the family—the tree kangaroo. Found in the tropical rain forests of New Guinea and northeastern Australia, these shorter-legged, agile animals, so at home in trees, can leap some 30 feet [9 m] from one branch or tree to another. At night they descend to the forest floor, where they feed mainly on herbs and grubs.

Fast, Graceful, Efficient

When moving slowly, kangaroos seem ungainly and awkward. Their tail and short forelimbs become a tripod that supports their weight as they lift their hind legs forward. But they are graceful runners. When bounding along at up to 30 miles [50 km] an hour, they use their great tail to balance themselves. According to The World Book Encyclopedia, they “can reach a top speed of over 60 kilometers [38 miles] an hour.” In the case of a large kangaroo, a single hop at high speed may span from 30 [9] to 44 feet [13.5 m]—a leap that could almost pass for flying!

Kangaroos are not only fast but also efficient in their use of energy. Professor Uwe  Proske, of Monash University in Melbourne, Australia, says that a kangaroo’s oxygen consumption is actually more energy efficient at higher speeds than it is at lower speeds. Proske also calculated that “at 20 kilometres [12 miles] per hour or faster, the energy used by the hopping kangaroo was less than that of a four-legged placental mammal [a mammal that is born fully developed, like a dog or a deer] of similar weight, running at the same speed.” Because of the kangaroo’s energy-efficient locomotion, it can travel long distances without tiring. But how does the kangaroo manage to run so economically?

The secret lies in its long Achilles tendons. “It is as though kangaroos are hopping on pairs of coiled springs,” says Proske. Like those attached to a human calf muscle, the kangaroo’s Achilles tendons stretch on landing and compress during takeoff. Kangaroos hop at the same number of hops per second (about two for a red kangaroo) over a wide range of speeds. To go faster, they simply lengthen each stride. An exception is when a kangaroo is startled. Then it may take off with a few small, rapid hops for better acceleration.

Kangaroos are also expert swimmers. Not only do they use their powerful legs but they get additional propulsion by swinging their tail from side to side. When chased by dogs, kangaroos have been known to use their aquatic skills by bounding into a water hole or a river. Any dog brave enough to go after the kangaroo promptly gets shoved under the water by the kangaroo’s muscular forelimbs and five-fingered paws, each armed with sharp claws. John, mentioned at the outset, had two dogs that were almost drowned by a wild buck kangaroo when it took them on in a small reservoir on his family’s property.

The Marvel of Marsupial Birth

Although adults are tough and robust, kangaroos are extremely undeveloped and delicate at  birth. Resembling little more than a pink worm measuring about an inch long and weighing a fraction of an ounce, they are born hairless, blind, and deaf. Yet, thanks to its precociously developed forelimbs equipped with claws and its sense of smell, the tiny “worm” crawls instinctively through its mother’s fur and up into her pouch. When inside the pouch, it latches onto one of four teats. The end of the teat immediately swells into a bulb inside the infant’s mouth, locking it firmly in place for several weeks. Considering its mother’s mode of travel, a solid anchor is clearly an advantage! In fact, so good is this anchor that early observers assumed that the young grew from the teat!

Eventually, of course, the joey will grow to the stage where it will leave the pouch, although only temporarily at first. However, after seven to ten months, when it is fully weaned, it will leave the pouch permanently. But let’s go back in time to when the joey first anchored itself to a teat and see another marvel of kangaroo reproduction.

A few days after the newborn latches onto its mother’s teat, she again mates. The embryo resulting from this mating develops for about a week, but then it goes dormant—on hold, so to speak—while its older sibling continues to grow in the pouch. When the older but still unweaned sibling leaves the pouch, the embryo in the womb resumes growth. After a 30-day gestation, it also attaches itself to a teat, but not the one suckled by the older sibling.

Therein lies another marvel of kangaroo biology. The mother gives her youngest joey one kind of milk and the older one a different kind. Commenting on this, Scientific American says: “The two milks secreted by the separate mammary glands are quite different in volume and composition. How this can be achieved under the same hormonal conditions is an intriguing question.”

Where to See Kangaroos

If you want to see kangaroos in their natural setting, you must be prepared to leave the cities and go out into the Australian bush, or the outback. Foraging for grass and small plants, kangaroos can be found individually as well as in small groups or in larger groups called mobs, which are presided over by big buck kangaroos called boomers. Because kangaroos feed mainly at night and rest in the shade (where they are well camouflaged) during the heat of the day, a good time to see them is early in the morning or at dusk. But in cooler weather, they may be active throughout the day. Whatever the case, be sure to bring a telephoto lens and binoculars—wild kangaroos are very shy animals.

Of course, you can also see kangaroos at most zoos, wildlife sanctuaries, and national parks throughout Australia and in some other countries as well. Regular exposure to humans has made these kangaroos less timid, and so you should be able to get some good close-ups, perhaps even of a mother with a joey peeking out of her pouch. Larger joeys always win a smile when they dive into mother’s pouch, only to have their lanky hind legs stick out awkwardly, making mother kangaroo resemble an overstuffed shopping bag. (Young kangaroos seem to be all legs!) A handsome buck may even grant you an erect, stately pose. Who knows? You may even see a couple of big boomers standing as tall as their long, sinuous legs permit and having a sparring match—genuine boxing kangaroos!

But to many, the best sight is a big red or gray buck hopping at full speed. True, other animals may be able to run faster or jump higher, but with no other creature will you see such a remarkable combination of grace, power, and spring on just two mighty legs.

[Picture on page 17]

The secret of the spring in its step is its long Achilles tendons