I doubt if many people from anywhere in the world haven't seen an image of the koala. They are as iconic representatives of Australia as the kangaroo and emu - by the way, for Americans the last is not pronounced "eemoo", but "eemyou" and you can't imagine how confusing this mispronunciation is to Australians when we hear you say it this way on TV or in a movie.
Okay back to the topic. The koala - often miscalled a koala bear although it's not a bear or even related to the bears - is an Australian arboreal marsupial and it's remarkably cute to look at. It is an adept climber, lives on a specialised diet of eucalyptus leaves and, due to the low nutritional value of its diet, spends much of its time sleeping although it can move quite quickly when it wants to. They are perceived as placid, even lazy, as they sleep in among the tree branches with those at sanctuaries regularly trotted out and given to visiting VIPs and celebrities to hold, most of whom are lucky enough to get away with not being peed on.
So that's the standard view of the koala but there's more to it than that, of course. The koala is found in the coastal eucalyptus woodlands of eastern and south eastern Australia, ranging from south-east Queensland to south eastern South Australia. It has been reintroduced to the area near Adelaide and Kangaroo Island and in ancient times was also found in the south west of Western Australia. Northern koalas tend to be smaller in size and paler in colour and population density is very varied with those in Queensland, for example, being numerous in south eastern areas and uncommon in other areas while they are only common in The Pilliga State Forests in New South Wales, but, on the other hand, are abundant throughout Victoria.
They tend not to be social animals but mothers and babies remain together until the mother becomes pregnant again in one to three years. Pregnant and lactating females can be aggressive as can males in dominance battles over territory or breeding females but otherwise they tend not to waste energy on fighting.
Like all marsupials, the baby koala or joey is little more than an embryo when born and it (there is usually only one although twins do occur occasionally) makes its way from the birth canal through the mother's fur to her pouch where it attaches to one of her two teats and suckles until it emerges fully from the pouch at about nine months to ride on its mother's back or abdomen until fully weaned.
For relatively small animals, koalas have a large range of very loud calls to communicate and signal breeding availability. These can be heard as far as several miles away. You can hear some of their sounds here, here and here.
Sadly many populations of koala are being affected by the STD chlamydia which is having an impact on fertility but a recent breakthrough by scientists in Queensland raises the hope that a vaccine is on the way.
There's much more to know about these fascinating creatures and you could look here , here and here if you're interested.