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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Koalas, cars and the urban setting

Koalas are often killed by cars in towns where the speed limits are much lower as well as out of town on higher speed roads.

One issue for koalas coping with roads in an urban area, is that there is more happening to distract the koala and the person driving the car.  The koala has to process a variety of stimuli such as electric lights, dogs barking, children noises, other machinery or traffic, humans and animals walking about and probably an extremely fragmented home range.  A car approaching, even at only 60kph is probably just a part of the cacophony around them.

In these situations koalas often simply step onto the road directly in front of a car apparently without seeing it was there at all.  This is not because of poor eyesight, but because they cannot separate and deal with all the stimuli.  Think of it like very young children playing and how unsafe that is near the road because we know a young child is likely to become so focused on play they will not see a car approaching.  In a similar fashion koalas just focus on where the tree they need to get to is, rather than what may be in between them and this destination.

Koalas spend most of their time sleeping and digesting. When they move they are focused on where they are going, not on what is around them.
Koalas spend most of their time sleeping and digesting. When they move they are focused on where they are going, not on what is around them.

Koalas are often seen walking along a road (rather than across), or they are reported to simply stop and sit in the middle of a road and watch a car approach and stop in front of them.  Observing koalas, it would appear that their flight response is often very low as they don’t have a ‘sense of danger’.  This is discussed in the article on dealing with cars in more detail.

When the flight response is elicited in a koala they commonly give a leap in the opposite direction or any random direction and begin to run without checking to see if they have chosen a safe direction.  They will then attempt to run to anything that looks like a ‘tree’ structure.  In other words, something they can climb.  This makes sense because their brain tells them that getting up high is the safe response.  Once a koala rushes up a structure in fright it tends to then determine to stay there until well after dark.

Hence we see koalas sitting high up telegraph poles, on fences, or even veranda posts seemingly unwilling to move.  The more stressed that koala becomes, the less likely it is to come down.

This is the typical koala response:

  1. ignore everything
  2. react without thinking and get up high
  3. stay very still until late at night when all is very quiet

Roundabouts provide another level of complexity that is nearly impossible for a koala to cope with.  All the koala sees is their food tree on the other side and they attempt to move towards it.

It is up to us as drivers to take more notice of wildlife on the roads, as the wildlife are not going to learn our rules.

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