Chemically nosey

Koalas are specialist folivores. This means they eat a diet consisting of leaves, and in this case they have a narrow range of leaves that they are able to eat. Some people say koalas are ‘fussy eaters’, but the reason for their particular choices of which tree, and then which leaves in the tree they will eat, is fascinating.
We often think of the koala as being a laid back, relaxed, easy going creature, living a life of ease. This perception comes from putting a human interpretation on their postures and the amount of time they spend resting and sleeping.

A wild male koala chooses what leaves are chemically ok to digest.
It may look like easy pickings, but it’s a lot tougher than you might think.

The eucalyptus leaf, if studied closely is tough, abrasive and toxic. Have you ever plucked one of these leaves and felt it with your fingers?
The koala must put a lot of effort into grinding the leaves with their molars. The amount of wear on the molars is the most accurate way we have of determining the age of a koala. The wear on the teeth continues as the koala ages, and if the animal remains healthy and lives to an old age, their teeth may wear down so far they become unable to eat.

Every leaf has toxins that must be analysed before consuming. Wild male koala checking leaves while eating.
Every leaf has toxins that must be analysed before consuming.

It is fascinating to see that an animal that has a limited primary food source has actually adapted to living in a diverse range of habitats, and across such a range of climates. The koala is found living in tropical and subtropical areas of QLD, and yet also in areas around Canberra that snow in the winter, and even some of the drier areas of Victoria. We observe certain basic differences in the appearance of the northern and southern cousins, yet they are the same species.
Across this range of habitats there are around 14 eucalypts that are considered their primary food sources. Yet in nearly every area koalas live, there are usually only around 3 of the primary species that the koalas use in that area.
They are observed to feed from around 30 non-eucalypt trees, but again the species used vary from region to region.
Each eucalypt leaf contains a wide range of ingredients, including the things we would expect such as protein, complex carbohydrates and water.
They also contain high levels of tannin, tough fibres, oil and cyanidic substances (which convert into cyanide). Yikes, that sounds like a mouthful of poison doesn’t it? It certainly is, to most mammals, and you can be sure it even tastes that way as well.

Wild koala joey learning to smell leaves while mum is eating.
The first thing a joey learns is what the right leaves smell like.

It is interesting to note that when we pluck a eucalyptus leaf from a tree, we can tell very little about it’s make up without taking it to a sophisticated laboratory. It feels tough and a little dry, because they have a rough surface, but it actually has a high water content – often at least 50%. This means around half the food the koala eats, is actually water.
Most animals could not survive the toxicity of the eucalypt leaf diet, and even the koala has to be careful they to not exceed certain levels of eucalyptol (the main component in eucalyptus oil).
So how do they make sure they can cope with their diet?

Koalas have the ability to chemically analyse the contents of the leaves by smell. That huge nose is like a portable laboratory. If you get the chance to watch a koala feeding in the wild, you will notice how often they smell leaves before eating. This is a constant balancing act they must perform.

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Pap for a joey

Pap – one dictionary definition of the word in general is “bland soft or semi-liquid food such as that suitable for babies or invalids.”

Koala mums don’t have the luxury of a supermarket and kitchen to prepare those first baby meals for their joey of course.

The koala digestive system is unlike that of most other animals.  We know that koalas eat leaves.  Do you also know that a joey drinks mum’s milk and nothing else for around 6 months while developing in the pouch?

Wild koala and joey that has head out of the pouch ready to eat pap.
Joey with head in perfect position for pap feeding.

Most animals that digest leaves and grass have 4 stomachs, and these animals are called ruminants.  Cows, sheep, goats, giraffes and kangaroos are some of the most common ones you might think of.

However, some animals that eat leaves have only one stomach, and they use a really big caecum to do this (that’s the appendix in us, which is tiny). They are called ‘hindgut fermenters’.  Horses, rabbits and koalas are common animals you know that are in this category.

The caecum and the large intestine are filled with microbes that turn it into a big fermentation vat.  This fermenting happens in the extra stomachs of ruminants and they are also called ‘foregut fermenters’.

It’s the microbes that are of most interest here.  Other articles will cover more about digestion.  Joey has been living a very sheltered life inside mum’s pouch, and has been drinking only her milk.  The microbes joey needs to digest leaves are not found in the leaves, so joey needs to get them from somewhere.  A goat kid will begin nibbling dirt within hours of birth and so begins to get microbes into their digestive system.  Not the case for the koala, as joey is still very fragile and high up in the treetops.

So mum has to provide the microbes joey needs to ready the digestive system for those tough eucalyptus leaves.

Wild koala mother and joey in this photo. Joey has head out of the pouch and is eating pap for the first time.
Joey is eating pap.

Joey knows when the desire to eat begins, and puts its head out of the pouch and begins to nuzzle around mums cloaca. (koalas have a single opening like birds and so it has the same name as we use for birds)  This nuzzling and licking stimulates mum to begin to secrete a pasty liquid directly from her caecum for joey to eat.  Koala faeces is shaped into firm pellets, but pap is a pasty semi-liquid.  It is really quite similar in texture to a puree made for a human baby just starting to eat.  However the reason is to kick start the hindgut in the fermentation process rather than to provide nutrition.  You could say, pap is a probiotic infusion.

We usually say that pap is a special faeces, but it is actually contents of mum’s caecum.  Probably not a big distinction for most people, but there is a difference.  Mum’s only produce the pap for a week or two at most while joey stimulates her.  Joey knows when it is no longer needed as joey starts to feed on leaves and is able to easily digest them.

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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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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.

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Koala dealing with cars

Koalas need to do fast calculations when going near our roads, as they try adapt to the modern world.
Koalas need to do fast calculations when going near our roads.

Once a koala is down on the ground and encounters a road, things really become seriously dangerous and complicated for them.  What is a road to a koala?

A bitumen road (or even a gravel road) is a foreign surface for an animal that was already not doing so well on the ground. The koala may hear a car approaching, but what does the koala brain do with this information?

I will talk about their hearing and mechanical noises in another post, but for the purpose of this post it is fair to say that hearing a car and knowing you are in its path becomes a more complex calculation than you might think.  As humans we know that a road means the path a car will travel along, the rules it will travel by (eg speed limits and which side of the road, depending on the direction being travelled), and we know what a collision with a car will mean.

Because of these facts, we can use executive thinking skills to quite quickly decide if it safe to cross a particular road.  We know it takes some mathematical calculation ability, and we know that a person affected by alcohol is unlikely to calculate this correctly either as a pedestrian crossing a road, or as a driver encountering a pedestrian suddenly.

We also know that many scientific studies have assisted governments to determine safe driving speeds on different roads by calculating the time it would take to stop a vehicle in an urgent situation according to the environment and the road conditions.

The only safe place for the koala is high in a tree as we see Enigma in this image.
The only safe place for the koala is high in a tree.

Let’s get back to the koala who is down on the ground, with their front-facing eyes and their mind on getting to the next safe food tree.  That koala does not have the kind of sense of danger a prey animal is wired to use when moving about, and so they focus on where they are going.

To the koala, a car approaching, when it is say 50 metres away, even if they can see and hear it, is unlikely to register as a threat to them.  They are unlikely at this point to even consider that it is on a course that will cross their path, even though they are on a road.  If we consider the speed the car is moving at, then a car moving at 100kph that is 50 metres away will be on top of the koala in less than 2 seconds.  There is no chance for the koala to calculate this and be out of the way in time.

Typical NSW country road - dual carriage with soft edges and lots of vegetation.
Typical NSW country road – dual carriage with soft edges and lots of vegetation.

Let’s add another layer of complexity.  The image above shows an intersection literally on a boundary of Koala Gardens. I want to examine a few important features as they are common roadside features our koalas deal with all over the NSW East Coast.

Firstly the amount of vegetation very close to the roadside is typical and an important consideration for the koala.  If a koala was in the vegetation on either the front right or on the opposite side of the road the driver would not see it as the vegetation is far taller than a koala.  This will also mean that the koala cannot see any car until it emerges from the vegetation at which time the koala is literally on the road.  The speed limit here is 80kph, so if the koala emerges and a car is 50 metres away, there is 2.25 seconds for the koala to get out of the way.

To the brain of a koala, an approaching car that went right past when it was sitting beside the road is no different, in terms of danger, than the approaching car when the koala has moved forward slightly and is now on the road.

Vandalised sign alerting drivers to be on the lookout for koalas.
Vandalised sign alerting drivers to be on the lookout for koalas.

There are no lights on country roads, so at night, unless the koala looks directly at an oncoming car, they are very difficult for the driver to see.  There are often thick fogs at night on these country roads which reduces vision for both the driver and the koala.  This is why we have road signs advising of known native wildlife, asking drivers to take extra care.

We have seen no evidence to suggest that koalas learn about road safety, or that they teach it to their young.

Finally we are not seeing enough evidence that people truly care about our wildlife.  This roadside sign is typical of the kind of vandalism we often see here, but shows a lack of empathy and understanding of how desperate the koala situation is.

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How koala eyesight impacts on them today

Koalas are trying to adapt to the modern world but their eyesight is made for the tree tops. Maxine and Enigma are pictured here showing koala eyes.
Koalas are trying to adapt to the modern world but their eyesight is made for the tree tops.

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.

Mist showing typical female koala head and eye shape
When a koala is awake they are usually hungry and needing calories.

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.

Even what they can see is usually distanced from them as they should be up in a tree.  Jordan is pictured here sitting in a tree looking at me without a care as I am on the ground and he is in a tree.
Even what they can see is usually distanced from them as they should be up in a tree.

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.

 

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Do koalas have good eyesight?

There is a reason koala eyesight is not so good over distances. Even when a koala looks directly at you, it will have heard you first, then had to find you by eye.
There is a reason koala eyesight is not so good over distances.

If you pose this question through Google the answer is pretty quickly returned as “no they do not”.

Now why might that be?

To understand why we need to consider the environment they had before humans came ripping through their homeland and changing everything.

Koalas are arboreal marsupials which means they live in trees, and are mammals that give birth to tiny under-developed young that crawl into a pouch to complete development for around 6 months.

Wild male koala looking down from a pink bloodwood tree - he can see me but koalas do not have good eyesight
Wild male koala looking down from a pink bloodwood tree

However, we need to think of incredible old growth forests thick with tall trees when we think of the arboreal koala.  When you live high in the canopy of a forest, there is not a lot you can see long range.  The ground is distant and hidden by the lower branches and smaller young trees.  Anything beyond the tree you are in, is likely obscured by branches and leaves from your tree or the next.

Stella is just over 12 months old and though she has bright eyes, she relies more on her hearing than her sight.
Stella is just over 12 months old and though she has bright eyes, she relies more on her hearing than her sight.

Koalas are far from blind, but their long range sight is pretty poor because it was not needed.  Koalas are skilled at jumping from trunks and branches to move about, and they look carefully to judge the distance before taking a leap.

Koalas have an acute sense of smell, and they do have keen hearing.  Sometimes it seems their hearing is not so keen because they sleep so deeply.

If you can imagine huge forests with hundreds of koalas moving through the treetops, you can maybe imagine that they didn’t bother looking to the ground or out into the sky too often.  Their focus was within the short range area of the tree they were currently occupying.

Koalas are said to have no natural predators, but this isn’t completely true.  However the only predators that were of any real concern to koalas in the past were usually only a concern for joey’s and small juveniles, and only if they were not in the treetops.  The main predators that may take a small number of young koalas are goannas, dingoes, pythons and some powerful owls and eagles.  The incidence of these predators seems to have always been fairly low.  Coastal pythons are the only one of these predators that may attempt to take a lone young koala in the canopy.

Stevie is looking at me, but it was sound that caught her attention fast, while it took her time to find me with her eyes.
Stevie is looking at me, but it was sound that caught her attention fast, while it took her time to find me with her eyes.

This all means that koalas do not have a historical need to be on a constant lookout for predator threats, and they do not hunt as predators themselves, and so their eyesight, for long distances is somewhat poor.

Another important feature of koala sight is that their eyes are ‘forward facing’ like our eyes. This puts the koala outside the general rule which says – ‘eyes to the side, run and hide; eyes to the front, love to hunt’.  Koalas don’t hunt, and yet they did not have any real need to run and hide either, and so they have eyes that face the front which give better depth perception. It’s also one of the features that makes them look so endearing to humans.

Enigma shows us a perfect example of the forward facing eyes of a koala. Koala eyesight however is not very good over long distances.
Enigma shows us a perfect example of the forward facing eyes of a koala.

The impact for koalas in adapting to the environment we have created by invading their home is huge when you understand their eyesight limitations.

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