Most adults carry scars from these encounters. They violently defend occupied trees. Males become quite aggressive during breeding season as they compete for females. They use their sternal scent gland as well as a loud barking call to mark their territory. Their low quality diet of leaves provides little usable energy and the koala typically sleeps 18 hours per day.
Females become sexually mature at about two years.
After a short gestation period the female licks a trail of saliva from the pouch to the cloaca. The joey emerges and follows that trail up to the pouch, where the mammary glands are. After about 5 months it climbs out of the pouch and onto the mother's back, where it stays until it is about a year old. It makes the transition from milk to solid food by eating partially digested leaves from the mothers cecum. Females bear one young every two years.