We have discussed the way koala eyes work, or rather how they don’t work as well as the eyes of either predators or prey animals. See koala eyesight post for more background information.
It’s more than their physical eyes however, it’s how their brains are hard-wired as well.
The koala is in an unusual position, being neither prey or predator on any real level. They are just going about their daily business of trying to get enough calories from all those eucalyptus leaves. In the process of doing this, they really are not taking much notice of anything else (except other koalas).
Let us now remember we no longer have large areas of old growth forest providing acre after acre of trees that can be accessed through the branches in the canopy, or at least by coming partway down and jumping across. The koala only had to see around itself, and use their highly developed sense of smell to know which trees were good and move through them.
The koala now finds itself too often, in a single tree, in the middle of an open paddock. He eats his fill, has a sleep then has to climb down to the ground and set off in search of the next tree which may be tens or even hundreds of metres away.
But let us think about the fact that the eyes of the koala are not made to make sense of this – they do not see well at long distances. Their brains are not wired up to think – this trip could be dangerous and tell their eyes to be really sharp either.
Yes a koala that lives well into adulthood is going to learn to traverse particular areas and deal with particular dangers, but the problem is that less and less koalas are living through their early encounters with the dangers on the ground. On top of this, the koalas are using up a lot more calories in order to take in each meal they find because they have to travel down the trunk, across the ground and then up the next trunk again. This is significant as eucalyptus leaves are low in calories and they have to eat a large quantity of them already.
When they are travelling they are usually hungry, and so their primary focus is going to be on getting to a good tree for their next meal. A koala with a full belly nearly always goes to sleep to aid digestion quite quickly.
So a koala walking through a paddock is needing calories and is unlikely to even see a dog coming for it unless the dog makes some good noise. A car approaching from a distance does not register with the koalas eyes at all. We will talk further about how koalas seems to respond to mechanical noises in another post.
Finally, when a koala does see something approach them, it is normally on the ground and they are up in a tree. Their tactic if concerned is to go higher up the tree. If they are on the ground, by the time they realise there is something of concern it is usually too late.
This highlights the importance of planting clumps of trees and rows of trees connecting good feed clumps together so that koalas can be on the ground for less time and eating more quickly.