Beginning at age three or four, the average female koala will bear one offspring per year. The gestation period lasts about 35 days. Once born, the "joey" is only about 2 centimeters long and weights less than one gram. The joey is blind, deaf, and completely hairless.
When the joey is "born" it crawls from the birth canal to the pouch. For the first six to seven months, the joey remains in the pouch and feeds only on the mother's milk. The eyes open by about 22 weeks. From 22 to 33 weeks, the joey feeds on pap. Pap is the mother's feces. By eating this, the joey's digestive system attains important microorganisms that will allow it to digest eucalyptus leaves when it is older. The joey continues to supplement its diet until it is one year old.
If the mother gives birth to another joey, the year old joey will leave to live on its own. If the mother does not give birth, the joey may continue to live with its mother for a longer period of time. When the joey becomes sexually mature, (for males 2-3 years, for females 2 years,) it leaves its mother and searches to find its own social and breeding group. Near this group the koala will claim a "home range." This consists of several feeding trees specifically claimed by a particular koala. The koala marks its territory with scent and scratches in the bark. The trees in overlapping "home ranges" become the primary locations for social activities.
The average length of the life cycle varies dramatically depending on the habitat of the koala. A koala living near a highway may only live two to three years, while wild koalas are estimated to live between ten to fourteen years.