Reproduction of Koalas (Phascolarctos cinereus)

By Mardi


Koalas live in a range of habitats from coastal islands and tall eucalypt forests to low woodlands that are more inland. Koalas are found along the south east coast of Australia. They eat eucalypt leaves because these are easily accessible in the treetops of Australian forest. Koalas are largely nocturnal and can live up to 18 years old in the wild. Because koalas live in the treetops they must be very strong so that they don’t fall down. Their habitat often does not have ease of access to water however being high in the trees they are protected from a lot of ground dwelling predators.


Koalas mate during summer, a dominant male will mate with all of the females in his territory. Koalas reproduce internally by cross-fertilisation where by the male inserts his penis into the female in order to release sperm that may fertilise an ovum by meeting and combining nuclei. It is most likely that only one egg is fertilised which means that only one or two ova are released. Internal fertilisation is an advantage to koalas because they live on land in trees with little water access and the gametes and/or the fertilised egg would dry up in the hot sun. Even if koalas found a way to avoid this there would be a chance of the developing embryo falling down from the treetops.


- reach sexual maturity at 646 days of age.

-usually give birth to one young per year

-Female koalas have two lateral vaginae and two ovaries that each have an oviduct, cervix and uterus.

-The two vaginae are the receptacles for sperm, during childbirth they fuse together to form the birth canal.

Diagram of female koala reproductive system


- reach sexual maturity at 1095 days of age.

-The penis is split into two sections, complementing the two lateral vaginae of the female.

-When flaccid, the penis retracts into the body.

diagram of male koala reproductive system


Koala’s have internal fertilisation and development. After 35 days of the embryo developing in the uterus (viviparity), the mother’s vaginae have fused together to create the birth canal. This is quite a short gestation period for mammals however the Joey is born into the pouch where it can remain protected, when born the young koala weighs less than 0.5 grams. In the pouch it feeds off its mother’s milk and as it gets older begins to feed on material passed through the mother’s digestive tract. When the young begins to feed on eucalypts rapid growth appears. Internal development of the embryo is a suitable method for koalas, it helps to protect the young from possible predators such as eagles and hawks and protects them from the harsh sun as well as cold of the winter, the pouch is very handy because it means that the baby can feed off its mothers teats and remain protected, the young will also not fall down from the tree. Viviparity results in a higher mortality rate and this is important as only one egg is fertilised.

young koala when born

Parental care

The Father leaves straight after mating with the mother and provides no parental care, however, Female Koalas provide a lot of parental care; they care for the Joey for 5 months in the pouch and the young will stay attached to its mother for up to a year. After that the young koala may live near its mother for another few months. After two years a young male is finally ready to survive on its own and will leave the area to find his own territory. It isn't surprising that the male provides no parental care whatsoever as he mates with several female koalas and it would be tough for him to provide parental care to so many young. The mother provides a large amount of parental care, this is common in mammals, marsupials, complex animals, animals that produce very few zygotes, and animals that use internal fertilisation and viviparity. A lot of parental care is a big advantage to koalas as they are moderately complex animals and need to develop strong muscles to hold themselves in the treetops while they chew on the eucalypts. Young Male koalas need a lot of parental care because by the time they leave their mother they have to venture off and find their own territory.


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