What does a koala’s nose know? A bit about food, and a lot about making friends

Ben Moore, Western Sydney University and Edward Narayan, Western Sydney University

The koala’s nose is distinctive – it’s a big black leathery rectangle in the middle of a round, grey face that’s surprisingly soft to the touch. And every koala nose is unique.

A study of 108 wild koalas found distinctive patterns of pigmentation around the nostrils allowed observers on the ground to reliably recognise individual animals, even when they’re in the trees.

Read more:
A report claims koalas are ‘functionally extinct’ – but what does that mean?

But more importantly for the koala, the nose is an important connection between this iconic marsupial and the world it lives in, from sniffing out toxins to saying hello.

And it starts right at birth. The tiny newborn koala, despite weighing only half a gram, already has the ability to smell and feel its way towards the milky scent of the pouch and its mother’s teats.

A koala’s nose knows how to sniff out toxins

Koalas, famously, spend most of their time sleeping or resting. When they’re not sleeping or resting, they are mostly feeding or moving between trees. In both of these activities – or in other words, for most of their waking hours – they follow their nose.

Koalas nearly always smell their food carefully before eating. So many koala experts were surprised to learn recently that koalas don’t have particularly many genes for olfactory receptors – the receptors found on nerve cells in the nasal cavity for detecting different smells.

Read more:
Koalas sniff out juicy leaves and break down eucalypt toxins – it’s in their genome

This matches up with anatomical observations that also suggest that among marsupials, the koala’s sense of smell is probably relatively poor, partly as a result of features associated with conserving water.

Gum leaves are chock full of natural plant toxins and other unpleasant chemicals, and koalas choose trees that minimise their exposure to the worst of these.

But most of the toxins that influence koala feeding are not volatile – they have no smell. It falls to the koala’s sense of taste (and genes for taste receptors are especially abundant in the koala genome) to make a final decision on whether a leaf is safe to eat.

Fortunately for the koala, the only-slightly-toxic compounds called terpenes (the invigorating scent of Eucalyptus oil) are highly volatile and offer a useful cue to the levels of other toxins in a leaf.

And one advantage of being a specialist feeder with a basic diet, is that there are relatively few odour cues to learn. It’s also fortunate the leaves koalas are checking out are right in front of their noses!

The koala’s nose might not only smell plant toxins, it may also play a minor role in detoxifying them.

Read more:
A cull could help save koalas from chlamydia, if we allowed it

We know enzymes in our own noses can detoxify certain drugs, and in other specialist herbivores, such as woodrats, many of the same enzymes that detoxify natural plant toxins and drugs in the liver are also expressed in the lining of the nose.

These enzymes likely help stop the nose from becoming overwhelmed by odours and maintain sensitivity. Critically, they also protect the central nervous system, as nasal tissue is the only thing separating inhaled toxins from the brain.

A koala’s nose knows how to make friends

Sniffing out food is important, but it’s not the koala’s biggest forte. So why the big schnoz? The answer may lie with the importance of social communication.

Although the koala genome has relatively few olfactory receptors, it’s rich in vomeronasal receptors, which are expressed in cells in the nasal cavity that are sensitive to moisture-borne molecules like pheromones.

Koalas are generally solitary creatures, but that’s not to say they don’t know their neighbours. Along with the distinctive loud bellowing of male koalas during the breeding season, olfactory communication is what koalas use to find or avoid each other.

A male koala’s breeding season bellow. Video: Denise Dearing.

Koalas of both sexes often spend considerable time smelling the base and trunk of a tree before they decide whether to climb up or move on elsewhere. When they enter or leave a tree, koalas commonly dribble a stream of urine down the trunk, leaving a trail of chemicals that potentially reveal information about the koala’s sex, identity, dominance, relatedness to other koalas, readiness to mate, disease status and even what they’ve been eating.

But if koala urine is a book written in scent, the secretions of the male koala’s sternal gland are more like a barcode.

This gland is obvious as a yellow-brown stained patch of bare skin in the middle of male koalas’ chests, and offers a straightforward way to tell the sexes apart.

It secretes an oily mixture of fatty acids and other chemicals, which are then transformed into an even more complex chemical mixture by the unique bacterial community occupying each koala’s gland. The end result is a distinctive bouquet and an unmistakable badge of identity for each koala.

Nose kisses from a koala

Aside from these fascinating nasal abilities, there is one more thing that we love about the koala’s nose.

When wild koalas are brought into captivity, they continue to rely on their nose to learn about the strange new world around them – that includes their food and branches, but also the scientists and carers moving around them.

Read more:
Drop, bears: chronic stress and habitat loss are flooring koalas

They will pull anything of interest into smelling range, making them one of the few wild animals that will rub noses to say hello with humans and fellow koalas, even when barely acquainted!

But wild koalas are highly sensitive to human handling, which can generate sub-lethal stress through the stress hormone, cortisol.

Without question, the koala’s nose is fascinating and a marvel of evolution, but no matter how strong the temptation to touch it, please leave those koalas in peace!The Conversation

Ben Moore, Senior Lecturer in Ecology, Hawkesbury Institute for the Environment, Western Sydney University and Edward Narayan, Senior Lecturer in Animal Science, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Koalas Under Threat

The link below is to an article looking at the threat to Australia’s Koalas.

For more visit:

A cull could help save koalas from chlamydia, if we allowed it

Desley Whisson, Deakin University

Whether it’s sharks, crocodiles or kangaroos, culling animals is always a contentious topic. But when the iconic koala is the species for which culling is being advocated, it sparks even more interest and debate.

Such was the case this week when researchers from Queensland and New South Wales published a study recommending that koalas be culled in the name of conservation.

Their proposal is for the selective culling of individual koalas suffering from chlamydia in an attempt to reverse the disease’s impact on vulnerable populations.

Koala chlamydia

Chlamydia is a sexually transmitted bacterial disease (a different strain to that which afflicts humans) that causes infertility and blindness in koalas, and is one of several factors thought to be behind the decline of koala populations in the eastern states. Koalas suffering the disease gradually become weak, stop eating, and die.

Although affected koalas sometimes may be found and taken into care, to date there have not been any systematic programs to combat the disease in wild populations. Given the negative effects of chlamydia on koala populations in some regions there is an urgent need to look at management options, including one that may seem quite radical – culling diseased individuals.

The current study considered a declining population on the “Koala Coast” of south-east Queensland. The researchers used computer simulations to model several disease management scenarios. The simulation that had the most positive effect on long-term population growth involved culling chlamydia-infected koalas that were already sterile and dying, and treating other infected koalas with antibiotics.

The study found that, to grow the Koala Coast population, around 10% (or 140 individuals) of koalas would need to be captured and culled or treated each year.

Killing for conservation

The idea of culling diseased individuals to manage disease and its impacts on wildlife populations is not new, and has met with both success (such as with Chronic Wasting Disease in deer in North America) and dismal failure (in the case Devil Facial Tumour Disease in Tasmanian Devils).

The effectiveness of these programs depends largely on the behaviour and ecology of the host species, and the distribution and nature of the disease. When enough is known about these aspects, computer modelling is useful for determining the potential effectiveness of a selective culling approach and for helping guide management actions.

But while modelling may inform us that culling is scientifically the best management approach, deciding whether and how to go ahead is complex, even more so when koalas are involved.

Koala management is closely scrutinised both nationally and internationally. The koala is the only native Australian species for which culling has been consistently dismissed as a management option (for overabundant populations in the southern states).

Although the current proposal for selectively culling diseased koalas isn’t “culling” as defined in the National Koala Conservation and Management Strategy, it still raises a question about killing koalas for conservation.

In 1997, culling was proposed as a component of an integrated strategy to manage high density populations of koalas on Kangaroo Island, South Australia. Despite having a sound scientific basis and the endorsement of many experts, it sparked much outrage and ultimately led to a decision at the Commonwealth level that culling will not be considered for management of koalas.

This decision has resulted in millions of dollars being spent on fertility control and translocation programs in Victoria and South Australia over the last two decades. These programs attempt to address situations where overpopulation of koalas is causing significant damage to local ecosystems.

Although some have brought positive outcomes after many years of intensive effort (for instance at Kangaroo Island and Mount Eccles in Victoria), these interventions are logistically challenging, extremely costly, and sometimes may have poor welfare outcomes for individual koalas.

Consequently, “do nothing” is the default management approach for many situations. But this can have drastic consequences for koalas, their habitats, and the other species that rely on those habitats.

Such was the case at Cape Otway in late 2013 when the Victorian government’s “do nothing” approach led to unsustainably high koala population densities, causing widespread defoliation of trees and the starvation of thousands of koalas. Around 700 koalas in irreversibly poor condition were killed when the government finally intervened on animal welfare grounds. Meanwhile, thousands of koalas likely suffered a slow death out-of-sight.

Although some trees recovered following the dramatic decline in koala numbers, high fertility has resulted in the population increasing again, and another imminent starvation event.

We do it for other animals, why not koalas?

Many wildlife researchers and managers would argue that a better approach for these situations would be to cull some koalas when it is clear that even more koalas will die if no action is taken.

This is not to suggest that culling be undertaken indiscriminately, nor in all situations. But it should be considered in circumstances where science indicates that it is the most effective approach to maintaining a healthy ecosystem and population of koalas.

It is the same approach that is used for numerous other native species in Australia and worldwide, so why shouldn’t it be considered for koalas, too?

Considering the outrage over killing Cape Otway’s starving koalas to reduce suffering, it seems that there may be little public support for culling koalas for any reason. It will be interesting to see how this new proposal to cull diseased koalas in Queensland and New South Wales will be received.

There likely will be opposition to culling and more support for a “treatment only” approach, despite its lower predicted effectiveness. However, one would hope that decision-makers place more weight on the scientific rigour of the research behind the proposal rather than the emotive argument that it is wrong to cull koalas.

The Conversation

Desley Whisson, Lecturer in Wildlife and Conservation Biology, School of Life and Environmental Sciences, Deakin University

This article was originally published on The Conversation. Read the original article.