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.
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.
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.