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.

What do koalas hear?

I have been fascinated by how koalas respond, or do not respond, to sound, when I have been out koala spotting.

It would appear that koalas have a decent ability to hear. They have large, mobile ears and when awake I have found they can hear footsteps, twigs snapping or voices quite acutely.

However hearing is more than the mechanics of the ear perceiving vibrations. Hearing is also the brain interpreting those vibrations.

I have mentioned in other articles here that koalas are neither prey nor predator animals. If we consider this when observing koala behaviour in relation to hearing, it does shed some light.

Prey animals need to be alert as much of the time as possible, and they will particularly need to be alert through their hearing when they are resting and sleeping.

Predators need their hearing for hunting. They may need to hear smaller animals moving through dense bush for example.

Koalas also become familiar with sounds in their own home range and learn to filter out sounds that their experience tells them is not a threat. This is important in understanding that hearing is as much the brain interpreting sounds as the ear detecting the vibration.  I have researched this topic and found little, so have conducted my own research with the koalas here in my daily spotting.

Compare the posture and expression on Legion in the video above to Pinky in the photo below and you can see the difference in response to sound, through being familiar with the sounds.

Photo taken on the first day Pinky was seen on the property.
Pink’s first day here and she is very alert to sounds as nothing is familiar.

An observation I have made with many different koalas over a range of years is that I can elicit a strong reaction from a koala that is new to the property with certain sounds such as pretending to sneeze, cough or even growl. However, with repetition, over a period of time, the reaction will decrease and for many koalas the reaction will completely cease. This means a koala that arrives at the property may startle and stare at me, then move up the tree if I approach and make a sneezing noise. If I repeat this each time I approach on different days, it may take as little as 3 or 4 days for the koala to completely ignore the same noise. Some koalas take longer to reach a point of ignoring me, but I have noticed that every koala will have a significantly reduced response within 3 or 4 days of me approaching and making a particular noise.

There are however, some types of noises they will always respond to, such as stomping footsteps approaching the base of the tree, particularly if long grasses are rustled and twigs snapped. Even though koalas are not truly prey animals, there is an instinct to understand that anything that can make heavy footstep noises, and is approaching the tree, is a possible threat.

Mist peering at the camera after been awoken by stomping footsteps.
I had to make stomping noises to get Mist’s attention as she is very familiar with me.

This does not mean that the footsteps are the loudest noise, at the time.   I have often witnessed a koala ignoring the sound of the quad bike approach the tree, but jumping from the bike to the ground and stomping has brought the head up immediately. The bike motor had obviously been making a far louder noise, yet had been ignored.

The next article will discuss koalas and machinery noises, as this becomes important in understanding another layer of why they are at such risk with cars.