Koalas and machinery noises

As mentioned previously, hearing is more than the physical process of vibrations being perceived inside the structure of the ear. Hearing is also about interpretation of those vibrations, and the how brain filters the vibrations our ears physically perceive. (How the brain filters and makes sense of what we, and in this case the koalas, hears.)

The history of the koala as an arboreal (tree dwelling) animal with little predator threat has influenced their hearing filters and reactions to what they hear. From the heights of the treetops, koalas filter out noises such as cars and other motorised vehicles going past. Roads encroach so much koala habitat that many koalas find themselves sleeping in places where there is almost constant vehicle noise.

Koala sleeping deeply in fork of a tree within sight and earshot of a busy road.
Koala sleeping deeply in fork of a tree within sight and earshot of a busy road.

Have you ever driven along a busy road and seen a koala fast asleep in a tree right beside that road?

By the same filter, a koala does not really differentiate between the sound of a car, chain saw, mower or bulldozer.

The koala has no way to figure that the bulldozer is going to knock down the tree it is in, when thousands of cars and other machinery have gone right past without incident.

In the same line of reasoning, the koala does not perceive they are in the direct path of the car approaching, when it is down on the road. The car sounds the same as the cars that went right past the tree all day long. The koala does not have the kind of executive thinking to figure that this spot on the ground is the place the cars were.

I have often seen a koala look up and watch me approach on the quad bike however. In nearly all instances the koala was already awake, and actually sees my face, and sees me looking intently into the tree. Any koala that has not become very accustomed to my presence will react to me, rather than the quad bike, and specifically to me looking directly at it.

Bullet has seen me approaching and looking at him so is now watching me. Bullet is a wild male koala.
Bullet has seen me approaching and looking at him so is now watching me.

I have tested this by looking away and riding past the tree, then looping back around and being sure not to directly look at the koala or the tree. The koala will nearly always relax, at least to some degree.

I always obtain a much bigger response if I approach the tree on foot.

An individual koala will have variations to their hearing filter depending on the particular habitat they live in and what is normal there. This means a koala that lives in a forest that is isolated from roads completely may respond differently to machinery noise if it is something they do not normally hear at all.

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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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