
Kangaroos
Kangaroos are the symbol of Australia. They adorn its postage stamps, coat-of-arms, coinage, and even its major international airline. At the zoo or in their natural habitat of Australia (and New Guinea), they remain the most recognized and obvious of Australia’s fauna.
Their faces, the way they carry their young in a pouch, their phenomenal leaping power, and their deadly ‘karate kicking’ have long intrigued people.
The whole family is best known as the Macropodidae—literally the “big-footed” family. This includes not just the six largest living species commonly called “kangaroos,” but also a further 48 species found in Australia alone, and another 13 found in New Guinea—67 modern species in all.
The range of two Australian species, the agile wallaby and the red-legged pademelon, spills into New Guinea as well. The term ‘modern’ is applied because this vast empire was once much greater, with over 100 species in Australia alone.
The term ‘wallaby’ is applied to those species where the adult male has a body mass less than about 20 kg (44 lbs) and feet less than 25 centimeters (10 inches) long. However, scientists can recognize no major anatomical difference between these and kangaroos.
Kangaroos’ superb design, their sophisticated reproductive methods and their amazing, energy-efficient locomotion did not come by any evolutionary process. For example, unless the pouch and the joey’s ability to find it were fully functional, they would have left no offspring.
They varied enormously in size. The tiny, scampering musky rat-kangaroo still lives in the tropical rain-forests of northern Queensland (Australia). However, the massive, blunt-faced Procoptodon is extinct.
Three basic size ranges are recognized today. At the other end of the scale from the six large types mentioned above are the rat/rabbit-sized bettongs, potoroos and rat-kangaroos. In between are the tree kangaroos (a specialized group comprising nine species that live and move about in the trees), and those commonly called wallabies.
Kangaroo Reproduction—Why the pouch?
In the desert species, carrying the baby in the pouch is convenient for the female, who may travel many miles for fresh food and water. The youngster stands a greater chance of survival because it does not have to keep up with her and is tucked away from predators.
During prolonged drought, kangaroos stop breeding. In some species, a doe [the female] is able to delay the development of a fertilized egg inside her until an older joey dies or vacates the pouch.
This remarkable phenomenon occurs in the red kangaroo, the eastern gray kangaroo, the common wallaroo (euro), the brush-tailed bettong, and several of the larger wallabies. It has also been noted in the honey possum and some non-marsupial mammals such as bats and seals.2
Another incredible aspect is that the doe can determine the sex of her offspring. How she does this is unknown, but she tends to put off bearing males until she is older. Males move away after about two years, but females stay with their mothers longer and benefit from ongoing support.3
A doe is nearly always pregnant. From sexual maturity to death, she is rarely without three offspring—an embryo in the womb, a joey in her pouch, and a larger youngster at her heels.
The joey is born after a gestation period of about 35 days (depending on the species) and in the largest species is the size of a human thumb nail. In the smallest, it is only the size of a rice grain. Naked, blind and deaf, it must make its way unaided from the birth canal to the pouch.
All going well, the climb will take less than 10 minutes. The joey can survive only a few minutes unless it reaches the pouch and attaches to one of the four nipples. Once there, its mouth swells on the nipple so that it cannot be removed without injury. A ring of strong muscles, similar to human lips, seals off the opening to the pouch to protect the joey from bouncing out, and keeps the pouch waterproof if mother goes for a swim.
After three months, the developed joey emerges from the pouch to make short trips in the outside world. However, it will return to the pouch to suckle and sleep until eight months old.






