Koala Reproductive System

By Marla Kennedy


Koalas are found from a variety of coastal islands to all types of eucalypt forests. Today they are found in Queensland, New South Wales, Victoria and South Australia. Like humans, koalas live in societies, so they need to be able to interact with each other. This is why we need areas of large eucalypt forests to hold a healthy koala population. Koalas are very fussy eaters and have strong preferences for different types of gum leaves, which make eucalypt but also non-eucalypt suitable habitats. Different species of eucalypts grow in different states, so a koala’s diet is adjusted to where they live. Eucalyptus leaves are very fibrous, low in nutrition and to many animals, poisonous. To cope with this, koalas are equipped with a large appendix to digest this.


Koalas reproduce by cross-fertilisation. The breeding season takes place from October to May. In koalas, the male sperm are placed in the body of a female and the eggs are fertilized internally. Two gametes are released during this process, which adds a bit of variety for the offspring because of the mix in DNA.


Koalas are viviparity creatures that develop in the mother’s womb. Their gestation period usually lasts for about 35 days. The embryo develops in a yolk-sac and when born, the offspring remains hairless ear-less and their eyes sealed shut. Unlike humans and those animals collecting nutrients with a placenta, there is no nutrient exchange between the mother and the fetus. Pregnant koalas benefit largely from the environment they live in. Growing in the mother’s womb while surrounded by trees gives good protection, it also gives easy access for all the mother’s needs, e.g. food.  An advantage of this strategy is that koalas have a very good sense of smell and hearing, so this eliminates any threats from reaching the developing young such as dingoes, pythons and wedge-tailed eagles.

Parental care

Koalas require a lot of parental care after birth. They are k- selection, giving birth to one at a time, the young being extremely premature. They are therefore unable to live independently and stay with the mother until they receive enough nutrients. Immediately after birth, the joey makes its way into the mother’s pouch where it will stay for about 22 weeks. As it is blind when it’s born, the joey relies completely on its well-developed senses of touch and smell. An advantage for this strategy is that it is well protected from predators while growing independent.  

Interesting Information

Koalas are not bears. They are not placental mammals, but marsupial, which means that their young are born immature & they develop further in the safety of a pouch. It’s incorrect to call them koala bears - their correct name is simply 'koalas'.

Younger breeding females usually give birth to one joey each year, depending on a range of factors. However, not all females in a wild population will breed each year. Some, especially older females, will produce offspring only every two or three years.

Koala young are known as ‘joeys'. Scientists often refer to them using terms like ‘juveniles', ‘pouch young' and ‘back young'.

The joey stays in its mother’s pouch for about 6 or 7 months, drinking only milk. Before it can tolerate gum leaves, which are toxic for most mammals, the joey must feed on a substance called ‘pap' which is a specialised form of the mother’s droppings that is soft and runny. This allows the mother to pass on to the joey special micro-organisms from her intestine which are necessary for it to be able to digest the gum leaves. It feeds on this for a period of up to a few weeks, just prior to it coming out of the pouch at about 6 or 7 months of age.

After venturing out of the pouch, the joey rides on its mother’s abdomen or back, although it continues to return to her pouch for milk until it is too big to fit inside. The joey leaves its mother’s home range between 1 and 3 years old, depending on when the mother has her next joey.

Female koalas are fully mature by about 2 years of age and males by their third or fourth year. By this time they need to have found their own home range, either in a home range left vacant by a dead koala or in a new area of the forest. This is one reason why koalas need quite large areas of habitat.


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