young and mature male koala scent glands shown for comparison

The koala nose

Scents are important to koalas and their sense of smell is highly developed.  We are all aware that they have large noses dominating their faces, and that is not coincidental.

The sense of smell is used for two main purposes – communication and chemical analysis of a potential meal. In both cases the ability to conduct a degree of chemical analysis is involved. This means the koala olfactory ability is above most mammals.

Koalas are solitary animals, yet they do live in a colony. This means they recognise the other colony members, and therefore distinguish koalas that are strangers. They are highly unlikely to do this by sight because their solitary arboreal nature means that they may not really ‘see’ each other often. They do however recognise the smell of other koalas. They also recognise the bellow of other males.

Most of the time however, koalas are quiet. Yet a koala does not move through the territory of another koala unnoticed, even if it makes no vocal sounds.

How does one koala know it is moving through another koala’s territory you might ask? How does a regular colony member know another koala has been in their territory?

We observe that both sound and scent are used to communicate more during the breeding season – a time when koalas are actually communicating the most. However, koalas have a home range within their colony area and they have home trees within their home range.

How does one newcomer know a tree ‘belongs’ to another koala? It must be by some method that humans are not aware of unless they were to be come a scientist (even a citizen scientist) and begin to study what is going on.

A terrific thing about using scents to communicate is that it is not directly threatening, and it conserves energy. Koalas will use both scent gland and urine to mark territory, but the messages they leave behind are probably more complex than simple ownership.

Whenever we observe a koala moving on the ground from tree to tree, we notice the koala will take some leaps and bounds, then stop and smell the ground and shrubbery at intervals and so on.

Pictured are two male wild koalas showing the difference in size between the male scent gland used to mark koala territory and advertise their availability to females within the colony.
You can clearly see the difference in size of scent glands between these two male koalas.

Every koala has a subtle difference in the chemical composition of their smell, making their own scent as unique as their fingerprint. Colony members remember this individual scent because they not only smell it once, but they smell it in layers if you like. A tree will be marked with scent whenever the koala enters and exits the tree. This builds up these layers of scent. These layers add a lot of meaning to the scent as they advertise clearly that a particular koala owns a tree, or uses it frequently. A koala can also tell how recently the scent was left and so have some idea of whether the owner of the scent is likely to be about.

A male koala will rub his scent gland over trees belonging to other koalas in order to leave an indication that he passed through in a similar way to other mammals that use urine to mark territory and indicate their availability for breeding.

When out in the bush even you can sometimes ‘smell’ a koala about, particularly during the breeding season.

While only males have scent glands, and only mature males have well developed glands, all koalas have a highly developed sense of smell.

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