Biology

Koalas are primarily nocturnal, spending most of their time in the branches of trees where they can feed, rest and gain some protection from ground-dwelling predators (6). Much of a koala's time is spent sleeping, and when awake they are still a fairly sedentary species. An adult consumes about 500g of fresh leaves per day (3). Koalas feed on a variety of trees, but the bulk of their diet comes from only a few eucalypt species (6), with marked local and regional differences for the species of eucalypts preferred (5). Eucalyptus leaves are very fibrous and highly toxic, but koalas have evolved to cope with these problems with special cheek teeth that grind the leaves into a fine paste, which is then digested by microbes in the caecum part of the intestine which is unusually long, at around 200cm, and has a blind end, unlike the caecum in most other mammals. Some of the poisons are detoxified in the liver. The diet does not provide much energy, but the long periods spent sleeping, along with their relatively small brains, help compensate for this (3). There is also evidence that suggests koalas may perform myrecism - regurgitating and re-chewing partially digested food, which extracts more energy from the food (7). Both males and females reach sexual maturity at around two years old, but males are rarely large enough to compete for mating access until four years old. Females normally give birth to one young every year but in older females this may reduce to one every two years. The newborn 'joey' is underdeveloped and crawls rapidly through the mother's fur to her pouch, where it suckles for six months. During weaning, in addition to milk, the joey feeds on a substance called 'pap' which is a liquefied form of the mother's faeces and provides the joey's digestive system with the micro-organisms necessary for digesting the eucalyptus leaves (4). Having first left the pouch during this time, the joey rides on its mother's belly, and later rides on her back. It normally remains with its mother until the following year's joey has emerged from the pouch (3).