Although kangaroos and wallabies are distinct species, the name kangaroo is sometimes used to refer to other species in the super-family called macropods. This includes wallabies, pademelons, wallaroos, forest wallabies and tree kangaroos.
Marsupials give birth to young that are much less developed than those of other mammals. Most of the early development occurs in the mother’s pouch rather than in the womb. For a kangaroo, gestation is only 31 to 36 days; that’s the equivalent of a human baby being born after just seven weeks!
After gestation, the mama kangaroo gives birth to a tiny little joey no bigger than a butter bean. Only its forelegs show any development to speak of; it is blind, hairless and its hind legs are little more than stumps – so it looks more akin to a worm than a baby!
Possibly wallabies, but they’re so gorgeous we had to include them anyway!
The first task in the life of the newborn joey is to find its way up to its mother’s pouch (which opens forwards rather than backwards like those of koalas and wombats). It does this by using its underdeveloped forelegs and claws and clambering up mom’s fur to her pouch. Unbelievably, the minuscule joeys accomplish this herculean climb in an average of just three minutes!
Once safe inside the pouch, the joey fastens itself to one of its mother’s four teats so that it can suckle and gain the nourishment it needs in order to grow. The pouch is what the baby kangaroo will call home for as long as nine months. At first, the joey stays permanently attached to the teat, only later learning to unfasten and reattach itself.
During the following months, the joey grows first single hairs and then fur while its powerful hind legs begin to develop. When it has grown enough (after over six months, and following a few weeks of cursory peeks at the outside world!) the joey makes its emergence from the pouch. It then starts to spend time exploring its new surroundings, returning to the warmth and safety of the pouch, until it eventually leaves permanently.
Interestingly, mother kangaroos are pretty much permanently pregnant, barring the day on which they actually give birth. They are ready to mate again – and often do so – immediately after the birth. Most of us would shudder at the idea of permanent pregnancy, but for mama roos it’s par for the course.
Again, we’re not sure if this is a kangaroo or one of its smaller cousins, the wallaby
In a special process called diapause, mama kangaroos are also able to pause the development of one embryo until the first joey leaves the pouch. This often occurs when food and water is scarce.
And there’s even more to the super-moms that are kangaroos: they can suckle two joeys of different ages – at the same time. Just as human moms give age-appropriate formula to their babies, so mama kangaroos produce age-appropriate milk for their joeys – but they do so through different teats that yield two types of milk: high-fat for the newborn, and high-carb for the older youngster.
As suggested, once the joey is big enough to go out exploring, it still returns to the pouch for safety and nourishment, although gradually it spends more time outside. Later, when it has left the pouch for good – after seven months have passed – it will suckle for a further four months, meaning it will be at least a year old before it is fully weaned.
Joeys are pretty big before they leave the pouch for the last time, so it takes some gymnastic ability for them to be able to get back in. They go head first, do a complete somersault, and end up with their head near the opening of the pouch.