The University of Wisconsin La Crosse (UWLAX) states that koalas reproduce through mating. Males bellow to attract a mate and use their dark scent glands, which are found in their chests, to mark trees.
By marking their scent on a tree, male koalas warn other males that the tree is occupied by a dominant male, the UWLAX explains. Males usually fight for a mate. The alpha male has multiple mates within its home range and sometimes hinders other males from mating.
The Koala Worlds says that koalas generally mate between December and March, and they are ready to mate between 2 and 3 years old. Deep bellowing calls and scents are used by males and females to attract one another. The males initiate these actions and wait for the female koalas to respond. Males become highly aggressive during the period when they search for mates. The mating ritual is usually short, and males are often seen biting the back of the neck of female koalas. Actual mating lasts around two minutes, after which both male and female koalas separate ways. Koalas typically avoid mating when they do not have sufficient food or when they feel stressed.
The Palomar College website states that koalas have a short gestation period that lasts between 34 and 36 days. They generally bear only one baby, called a joey, per year.