General Koala Information


Koala (Phascolarctos cinereus)

The koala is a tree-dwelling, folivorous marsupial found in scattered populations along the eastern seaboard of Australia – from west of Cairns in far north Queensland through to South Australia. More isolated populations are also found on the tablelands of the Great Dividing Range and the western plains of both Queensland and NSW. Koalas are found across Victoria and populations on mainland South Australia as far as Adelaide. There are also populations relocated from the mainland to islands off Queensland, Victoria and South Australia.

Due to habitat loss, the koala is now under threat, making it a sentinel animal for forest-dwelling species in this country. Basically, if the koala is wiped out, whatever (and whoever) is responsible for its eventual extinction will also precipitate the demise of other fauna and flora. Australia holds the shameful title of having the greatest number of extinctions of mammals in the world.

Koalas show marked clinal distribution as a result of latitudinal changes (i.e. climatic differences). Queensland koalas are smaller than their southern counterparts (males average 8kg) and have finer fur to stay cooler. NSW koalas are mid-range in size (males up to 10kg) with slightly thicker fur. Victorian koalas are larger (males up to 14kg) and have thicker and denser fur in adaptation to the cold.

The koala’s diet consists mainly of eucalypt leaf but they will feed on Melaleuca, Corymbias, Allocasuarinas and other species as well. They will also consume the flowers, nuts, bark and stems. They are also known to consume occasional exotic foliage such as New Zealand Christmas bush.

Of the 900 or so eucalypt species found in Australia, koalas will only feed on a small percentage of them as various eucalypts can carry a high load of toxic compounds that the koala finds unpalatable. Other trees are unpalatable simply because of where they are growing and the lack of leaf moisture that will not sustain a koala. Even favoured species can be unavailable during certain times of the year, when they too have high levels of compounds that the koalas have to avoid. Koalas obtain most of their water needs from the moisture levels within the eucalypt leaf, so the majority of koala populations are located near water courses or wetter areas. Koalas found in inland areas of Australia certainly struggle, with large numbers lost every time there is a severe drought or fire event. As temperatures are rising in Australia and weather conditions such as more frequent droughts and bushfires are occurring, the future of the koala is even more uncertain.

Social Structure

Even though koalas are seen as solitary animals, they actually live their lives as part of a dynamic, ordered hierarchical system.

Each koala within the population lives in an individual home range. The home range size is dictated by the age, sex and social standing of each koala which includes the amount of trees, how far apart they are located and what use they have. A koala occupies its home range for life unless pushed out through age, infirmity or habitat removal. All home ranges within each population overlap at various points. Koalas also vocalise to each other, so communication for this animal is an integral part of daily life.

The fittest, biggest and most virile male koala is the alpha male. He occupies the best quality habitat, which is usually the largest in size with his territory overlapping the home ranges of 3–4 higher ranking breeding females.

Often there is an alpha female, a healthy, fit, fertile, breeding koala who occupies prime habitat adjacent to the alpha male. It is necessary for all breeding females to obtain good-quality habitat. Lactation takes a lot from an animal living on a low energy/low nutrient diet, so a breeding female’s range must be able to sustain both herself and her young.

One of the alpha male’s jobs is to protect his females in exchange for mating rights.

Lower ranking males and females usually occupy lower quality ranges that are often located adjacent to each other.

Younger females are usually better accepted in finding habitat within or adjacent to the core breeding colony. If available resources are limited this is not always the case as they can then be marginalised.

Young subadult males tend to be pushed out onto the edges of the population to exist on poor-quality marginal habitat. They tend to “lie low” for a number of years until they are sexually mature. It is during this vulnerable period of dispersal from their maternal home range that many young males have great difficulty surviving and often die. It is not unusual to find young subadult males a very long way from the maternal range (some have been recorded more than 30 kms away) and it is these young animals that are commonly found in a distressed state, in poor condition and running up busy urban roads desperately seeking unoccupied areas to inhabit.

Where forested areas are plentiful, subadult animals can disperse and radiate out into unoccupied habitat and thus new colonies can develop. Alternatively they can move into other populations. When immigration and emigration between populations occurs naturally and freely, this outsourcing of blood lines invigorates each population and maintains healthy genetic integrity. As more and more vegetated areas are removed, it increases the pressure on koala populations to remain genetically viable and healthy. Urban populations can sometimes become genetically poor “islands”, with koalas unable to disperse, radiate and mate with unrelated animals. Koalas in these environments are also forced to live closer together with not enough food trees to sustain them.

This genetic and social pressure adds to the multitude of problems koalas face daily due to habitat loss. A massive increase in disease expression is one obvious result, with chlamydial infections being a prime example.

As the koala’s low metabolic rate does not allow for lengthy periods of physical exertion, fighting to defend territory

Does not commonly occur between male koalas as it is not in their best interests to do so. Where male home ranges overlap, contact between them is usually avoided, and if it does occur the scuffle is usually short-lived. Given that the weight of the alpha male far exceeds those of his lesser counterparts, few lower ranking males would be willing to take him on.

There is also a fallacy that only males bellow – this is incorrect. Female koalas at times can emit a low, repeated bellow which is usually heard during the peak of breeding season. More often she will emit a high pitched screeching scream when a male approaches which continues throughout mating and to the uninitiated it can sound quite terrifying.

Home range boundaries tend to be identified by scent gland and urine markings. Scratch marks on the smooth bark of trees and scat droppings are good indicators of occupancy of a site. Koalas certainly have favoured food trees, but not all food trees in a home range are used. Often non koala food trees are preferred for sleeping and refuge and these trees can offer good shade, warmth or even security. Particular trees on home range boundaries are critical as social interaction trees, are used for mating and are nicknamed “bedroom trees”. This is confirmed by reports from tired, cranky home-owners who often complain of suffering sleepless nights during koala breeding season. The sounds of grunting, amorous male koalas advancing on protesting female koalas are broadcast from the same trees on and off for several weeks with repeat performances every year. Such is the joy of living alongside both rural and urban koalas. Mating season varies but usually commences in late winter and goes through until late summer, with the peak of activity in early spring.

The male koala rubs his sternal scent gland (a useful tool for identification of sex from a distance) along branches and trunks to mark boundaries. Juvenile males do not have a prominent gland, instead possessing a crease in the centre of their chest area. Sexually mature, higher ranking males tend to have prominent glands, which can become very greasy and sometimes even exhibit hyperplasia (an enlargement/overgrowth of normal cells) during breeding season. The glands of lesser ranking males are not usually as large, nor do they glisten as excessively with oil. Although the scent emitted by this gland is obviously attractive to koalas, it is rather offensive to humans with a smell akin to an entire football team’s week-old footy socks!

The highly stylised diagram opposite is an approximation of how colonies of koalas are ranked and how the home ranges are organised on hierarchical grounds. Note that the dominant, higher ranking animals have the biggest area. These ranges overlap each other, forming the nucleus of the population. Removal of habitat destroys this social order, forcing koalas closer together or further apart, reducing the availability of resources and increasing their chance of disease expression. Taking out large tracts of habitat creates a domino effect that influences all koalas in the population and will easily have repercussions on neighbouring populations. Urban and peri-urban koalas become “refugees” when their habitat is continually removed.

Coastal home ranges can be anywhere from a few hectares to up to one hundred. Koalas located on the plains west of the Great Dividing Range and inland Victoria are possibly even bigger.

Adult koalas that have been in rehabilitation and are to be released must be returned to their original capture point or at worst very close by. An adult koala kept in rehabilitation for a very long period is at risk of having their home range occupied by another animal during their absence.

Gut System

There are four main marsupial species that feed on eucalypt leaf – the greater glider, the common ringtail possum, the common brush tail possum and the koala. Both the greater glider and the koala use eucalypts as their principal food source.

Koalas, a monogastric hindgut fermenter, not only have a large and complex digestive system (see Figure 3) to accommodate their diet of eucalypt leaves, their whole lifestyle has evolved around it. Starting with the selection of the right leaf type, the koala grabs a branch, then sniffs the leaf to check its quality (and toxicity level) prior to consumption. The leaf is broken off with a strong biting action, masticated, mixed with saliva to allow enzymes to begin the breakdown process, and then swallowed, before ending up in the stomach.

Koalas “chew” their leaf in a methodical size-reduction process. Provided koalas have unworn, sharp interlocking cusp points on their molars, this is done efficiently. Aged koalas with worn, flat teeth cannot achieve an adequate breakdown of leaf. The result is that such koalas cannot make use of their food and will basically starve to death.

In the stomach, acids and enzymes break down the masticated leaf further. It is at this stage that most of the toxic eucalypt compounds (such as phenols) are removed and redirected via the blood to the ‘super’ liver for processing. The toxic substances are excreted in the urine, which partly accounts for its strong smell. If consumed by other animals or humans, the phenols and other toxic substances found in eucalypt leaves would be fatal.

The food then moves via peristalsis (an involuntary muscle movement) into the small intestine where it continues to break down. Here, fats, proteins and other nutrients are absorbed into the bloodstream. The next destination is the interesting and unique caecum, a blind gut - section of intestinal tract that is closed at one end, up to 2 metres long, which is 23% of the total intestinal length. The caecum houses an amazing array of microorganisms whose purpose is to break down carbohydrates. The next stage is the proximal colon, which is also a site for microbial activity. Since koalas lack the digestive enzymes to break down cellulose and lignans, these microorganisms accomplish this via fermentation in the caecum and proximal colon, freeing up the carbohydrates for energy use.

Finally, the food waste moves into the distal colon (again, via peristaltic action) where water is extracted, some for re- use in the body. This efficient extraction of water from eucalyptus leaf is one of the reasons koalas drink very little water, allowing them to remain high in the trees and safe from predators. The final product is the dry, football-shaped droppings passed by the koala which eventually breaks down in the soil.

Koala faecal pellets have another use besides returning nutrients to the soil: two species of moths (and possibly more that are yet to be described) exclusively lay eggs in the pellets, their larvae feeding, growing and hatching out of the koala’s faecal material. Observing whether a faecal pellet contains fresh larvae or is simply a vacant shell is indicative of the pellets age, allowing researchers to determine how recently koalas were in the vicinity.

Nothing is wasted in nature and every component tells a story.

Genetic Diversity
Quintin Lau and David Phalen
Koala Health Hub, The Faculty of Veterinary Science, The University of Sydney
What is genetic diversity?

Genes are the building blocks of all living organisms and is the basic unit for heredity. Genes are made up of DNA, which has instructions for making proteins. Genetic diversity is the total genetic makeup of a species and is the most fundamental of the three levels of biodiversity (genetic, species, ecosystem).

Why is genetic diversity important?

Genetic diversity is important for a species or population to survive and adapt; especially to changing habitat or new diseases. If genetic diversity is low in a population, individuals become genetically similar and this increases inbreeding. There are 2 types of genetic diversity that scientists study: (1) neutral genes, which are more informative about population history, and (2) adaptive genes, which are related to the fitness of a species/individual and how they are affected by natural selection.

Koala brief history and current genetic diversity.

Koala populations were quite widespread before European settlement, but crashed in the late 19th century as a result of many human factors (hunting, habitat loss) and disease. Shortly after, translocation programs were established; mainly in offshore islands in Victoria, where a small number of koalas (reported to be as few as three individuals in some cases e.g. French Island) were the founding population in each island (this founding of a population with only a few animals is called a genetic bottleneck because it restricts the diversity of genes that make it through to the new population). Many koalas from island populations were later returned back to mainland Victoria and most of these populations have recovered even to the point of over-abundance in some areas (Martin and Handasyde 1999). As a consequence, the genetic diversity of koalas from southern Australia is low (both neutral and adaptive genes). The few populations in Victoria that have not been influenced by major translocation programs, such as in South Gippsland, have much greater genetic diversity, making those populations relatively valuable genetically (Lee et al 2011; Lau et al 2014).

In northern New South Wales and Queensland (‘north’), many koala populations are currently declining and are fragmented due to land development (development of roads and residential areas result in koala habitats being cleared and separated from each other). Overall, these koala populations have higher genetic diversity (both neutral and adaptive genes) than populations from Victoria, as they did not experience severe bottlenecks in the past (e.g. translocations on islands) and many populations in the north are genetically distinct from each other (the genes in one population are quite different to genes in a different population) (Houlden et al 1996; Lau et al 2014). Due to a decline in koala numbers in the north, populations in NSW and Queensland were listed as ‘vulnerable’ in early 2012 under the Australian Federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999.

What can we learn for the future?

Koala populations in southern Australia are considered to be thriving, but have a low genetic diversity. This means that these populations are potentially at greater risk to changes to the environment or new diseases (they cannot adapt as well due to their genetic makeup). It is important to continue monitoring and protecting these koalas. The history of the koala’s translocation programs show that current and future conservation programs of koalas and any other species must consider maintaining high genetic diversity for continual survival of the species.

Koala populations in the ‘north’ seem to be genetically diverse, although these populations are declining. Each small fragmented population that is lost is a potential loss of diversity forever, so it is important to continue to protect the koalas and their habitat to avoid loss of genetic diversity and maintain healthy, resilient koala populations.


Houlden BA, England PR, Taylor AC, Greville WD, Sherwin WB (1996) Low genetic variability of the koala Phascolarctoscinereus in south-eastern Australia following a severe population bottleneck. MolEcol 5:269-81

Lau Q, Jaratlerdsiri W, Griffith JE, Gongora J, Higgins DP (2014) MHC class II diversity of koala ( Phascolarctoscinereus) populations across their range. Heredity

Lee T, Zenger KR, Close RL, Phalen DN (2011) Genetic analysis reveals a distinct and highly diverse koala ( Phascolarctoscinereus) population in South Gippsland, Victoria, Australia. Aust Mammal 34:68-74

Martin R, Handasyde KA (1999) The Koala: Natural history, conservation and management. University of New South Wales Press Ltd, Sydney

Drugs and Koalas

We often get asked why we cannot “cure” some koala diseases and why we cannot give a number of drugs to koalas. Well this is why…..

Eucalypt foliage is very tough and contains a number of chemical compounds designed to protect the tree. These compounds are quite toxic and would kill the majority of animals (or people for that matter) if they decided to eat them. Koalas along with possums and gliders have evolved over millions of years the ability to live on a diet of eucalypt leaves without suffering any issues with the deadly chemical compounds.

So how does a koala cope with the toxins? With a super liver of course!

Koalas have developed an amazing liver that is quite big, has multi lobes and very complex. Its job is to breakdown and excrete all those nasty compounds and eliminate them from the body via the urine.

This liver works so well, that a number of medications that are given to koalas are metabolized, broken down and excreted out before they have any chance of reaching the bloodstream and doing the job they are designed to do.

And that’s not the end of the story………

Another part of the evolutionary story with the koala’s adaptation to living on a diet of eucalypt leaves is that they have developed an amazing gut system as well. As part of this system, koalas have a very big caecum which can be described physically as a 2 metre long appendix (but has a different role to the human appendix). This incredible organ is where all the chewed up eucalypt leaf is broken down properly, fermented and the nutrients are then taken up and used by the koala. The whole gut system of koalas is filled with an enormous amount of microorganisms called a microbiome which consist of millions of different bacteria and fungi. The majority of these live in the caecum and without this microbiome, there is no koala. Incidentally humans also have a very important suite of microbiota as well in our gut systems that are critically important to our survival, although ours are not as complex or as interesting.

The microbiome’s job is to break down all the fibrous material, and to make the nutrients available to the koala. A healthy gut system means a healthy koala (and a healthy human too while we are on the subject).

There are a number of excellent drugs that will certainly “knock down” diseases in koalas such as chlamydia but unfortunately these drugs also “knock down” koalas microbiota. The result? The koala dies.

Current research is suggesting that koalas in different regions of Australia have a different suite of microbiota to koalas in other regions. For example, koalas on the far north coast of NSW and S.E. Qld, are likely to have different microbiomes to koalas from the mid north coast of NSW. Koalas on the inland plains are likely to have different microbiota again. Koalas in various locations across Victoria and SA are also more than likely to have different microbiomes in different regions. Why you ask? It is likely driven by the microorganisms that occupy different ecosystems and forest habitats. A useful forensic tool maybe!

Anecdotally it would seem that koalas in some regions are more tolerant of various drug treatment regimes and who respond well to these drugs. Whereas in other localities the same drug is fatal if administered to koalas suffering the same disease. Could the potentially different regional microbiota be the cause? This drug research is very much in its infancy so we may find this hypothesis will completely change as this mystery unravels.

Consequently there are not a lot of drugs that can be given to koalas overall, where a successful treatment plan results in the desired outcome of the koala becoming “disease free”.

Research is also looking at ways to potentially re-inoculate the gut system with the correct microbiota if medications have caused issue. Small capsules (affectionately known as “crapsules”) filled with microbiota are being trialled to achieve this. This is the equivalent of humans taking probiotics but much more supercharged. At this point in time it’s still very much a work in progress.

All of this highlights how little we really know about the physiology of the koala. How can we improve our knowledge? Funded research and lots of it.

Reasons for Admission

Koalas in this country are now in serious decline with the key threatening process to their survival being land clearing and thus loss of koala habitat. This is not unique to koalas as all species of wildlife worldwide who are in decline are suffering the same plight as a result of removal of forests, climate change, pollution of oceans, and waterways. For koalas this loss of vegetation not only removes the trees that sustain them, but increases the chances of being hit by cars, attacked by dogs and suffering from diseases such as Chlamydiosis.

What is Chlamydia?

Chlamydia is an obligate, intracellular bacteria that is found in many species of bird and mammals worldwide.

For example, Chlamydia psittaci a species of chlamydia infecting birds particularly parrots, is also considered a zoonotic disease which can be transmitted to humans causing severe illness.

In humans, Chlamydia trachomatis also found worldwide, is considered a sexually transmitted disease affecting both the urogenital tract and the conjunctiva (eyes). Alarmingly, this disease is on the rise in developed countries in spite of good public education.

*Even koalas are not spared from this bacterium Chlamydia. Koalas suffer from two species of Chlamydia – Chlamydia pneumoniae and Chlamydia pecorum.*

For simplification it is suffice to say that within these two species are many strains and as research continues more are being discovered.

So how does chlamydia occur in koalas?

It is likely that many strains of this disease have existed for a very long time within koala population, acting as natural population regulators. In the early 1800’s Europeans settling in Australia brought with them agricultural livestock such as sheep, cattle and pigs. Records from this period reported koalas “curled up at the base of trees, with diseased eyes and looking very sick”. Research using DNA sequencing has shown that some of the current strains of chlamydia are very similar to those found in cattle, sheep and pigs. It is highly likely that these strains of chlamydia “jumped ship” from agricultural animals into koalas – how this transmission occurred is still largely unknown. These “newer” strains are considered to be more virulent exposing koalas to diseases they have not had enough evolutionary time to adapt to and thus the disease had a major impact on wild koala populations even as far back as the 1800’s. This scenario is similar to our first nation’s people of this country who were first exposed to European diseases in the 1880’s such as influenza with disastrous results.

Chlamydia can exhibit as ocular disease (infecting the eyes) or the urogenital form (infecting the reproductive tract and the urinary tract) or koalas can exhibit both at the same time.

Some koalas can appear quite healthy with no clinical signs of the disease but can still carry the pathogen ( sub-clinical) and may never become unwell during their lifetime.

Interestingly, a much higher expression of this disease occurs in areas of disturbed habitats such as peri urban ( beside) and urban environments, agricultural and mining areas with reduced vegetation, in areas of high bushfire impact and now in areas suffering from hotter, drier conditions. This higher expression of disease in these areas makes sense as koalas are either forced closer together to compete for resources or further apart and struggle to find food and shelter. Genetic inbreeding occurs in areas of fragmented habitat as does koalas forced to seek refuge in areas of poor soil and moisture quality. In good healthy forested areas that are undisturbed, the incidence of chlamydial disease is very low.

When koalas are first admitted into the hospital, they undergo a full health screen examination. This is done under anaesthesia with the koala given a full physical assessment, blood tests are done and a PCR swab (Polymerase chain reaction which detects chlamydia cells) and finally an ultrasound to check the urogenital tract and other internal organs that may be affected by this disease. If the koala does not have disease that is too far advanced to be treated, then the koala will commence a 4-6 week treatment plan. At the end of the treatment plan, the koala is held for a further two weeks and “left alone”, then the koala is given a full health screen under anaesthesia again and if everything has been deemed “successful”, the koala is eartagged, microchipped and released back to its capture point.


Bilateral conjunctivitis

So what do we look for?

In the ocular (eye) form of this disease the conjunctiva of the eye is normally the first point of noticeable infection. It becomes red and inflamed, the tissue begins to swell and a purulent (pus filled) discharge can often commence. As the disease progresses, it can invade the cornea (the front of the eye itself) and/or the conjunctival tissue creates an inflammatory response where the tissue becomes so swollen and prolific it completely covers the eye and the koala is unable to see. In advanced stages the koala is rendered blind and they usually starve to death as they are unable to locate trees. In the early 1980’s the Koala Hospital pioneered an excellent procedure where the damaged conjunctival tissue was surgically removed and even today this procedure is still considered an important part of the treatment plan and has been adopted throughout Australian veterinary clinics.

If the koala is admitted to care in the early stages of ocular infection, there is usually an excellent chance of successful treatment.

Urinary and reproductive tract infection is a much more complex scenario. Whilst the disease chlamydia does not favour either sex and will happily infect both male and female koalas alike, the female koala has “more plumbing” to deal with and therefore more complications can arise. There are many cases where koalas have become infected whilst in the wild and have recovered unassisted, with some not becoming unwell again into the future. Other koalas may also recover from a new infection, but it usually leaves some sort of residual structural damage to the bladder wall, the reproductive tract and even the kidneys. In future seasons the koala can become infected again either with a new strain of the pathogen or their immune system becomes compromised and the original disease “flares up” again. Every time a koala becomes sick, more structural damage is done internally, no matter how well they may appear. Some koalas become infected for the first time and become so diseased, they deteriorate and die in a matter of weeks. Much of how koalas respond to this disease is driven by genetics, soil quality and soil moisture/nutritional status of trees, multiple pressures from disturbance of habitats, climatic conditions and how virulent the actual strain of the disease is in the area they live.

Bear in mind here, koalas can have both the ocular and the urogenital tract disease at the same time as well.

The koala suffering from urogenital chlamydia will undergo a full health assessment under anaesthesia soon after being admitted to care.

If during this assessment the internal structural damage is so advanced, that the future quality of life for the koala is very poor then the kindest thing to do from an animal welfare perspective is to euthanase the koala whilst it is under anaesthesia. At the Koala Hospital (and across the country) relieving animals of severe pain is a major component of what we do.

So what is “internal structural damage”?

The healthy bladder wall of a koala is no different from any other species in having a thickness equivalent roughly to a rubbery thin balloon. This beautifully designed set of muscles is used to both hold and expel urine. In an infected koala the wall of the bladder can become so thickened and fibrotic that it becomes ineffective in both holding and expelling urine – the koala becomes incontinent and continually drips urine hence the term “wet bottom” or “dirty tail” to describe a sick koala. The internal wall of the bladder can also become so inflamed and swollen, the koala continually passes blood and purulent material. This sort of damage is simply not treatable with drugs and is both incredibly painful for the koala and distressing for the human carer to witness.

Wet bottom

Wet bottom

The disease can ascend into the kidneys causing renal disease and failure. Again, very painful and simply does not allow the koala to function as they should.

From a reproductive tract point of view, the male’s prostate can become inflamed, swollen, painful and obstructive to the flow of urine.

The female’s reproductive tract can become swollen and inflamed with females developing what are termed “paraovarian cysts”, which are cysts that are found beside the ovaries in the bursal sac that surrounds the ovarian tissue. These cysts can become enormous and have the capacity to occupy a large area of the abdominal cavity pushing and adhering to other organs. The fluids encased in these cysts can be filled with all sorts of nasty inflammatory material which not only can rupture, but they render the female totally infertile for future breeding. Female koalas can also suffer from pyometra (purulent material in the uteri).

As with the ocular form of the disease early intervention is the only thing that offers any sort of good outcome. More often than not koalas are not admitted until they have become seriously unwell as they behaviour dictates that koalas remain high in the trees until they feel so sick they come down low enough to be spotted by home owners who then report the sick koala.

Sometimes koalas can be admitted for independent reasons such as being hit by cars and as an incidental finding, a chlamydial infection is found as well (or was the koala on the road because it was sick?).

How do we treat this disease?

As a specialist folivore, koalas have evolved to cope with the toxic compounds found in eucalypt leaf by a number of mechanisms. Koalas have what is dubbed a “super liver” which is designed to breakdown and metabolise these toxins and eliminate them from the body. The koala also has a large gut system plus a two metre caecum filled with a suite of micro-organisms (microbiome) all designed to breakdown the leaf allowing uptake of nutrients.

There are a number of antibiotics that are capable of killing the chlamydia in koalas but have the potential to kill off the important microbiome and as a result can kill the koala. Treating koalas for this disease is difficult as there is a fine line between successful treatment and causing harm to the koala.

Other medications such as non steroidal anti inflammatory drugs are metabolised and eliminated by the “super liver” before they are able to do the job they are designed to do.

It is worth noting here that both the NSW and Qld koala populations are struggling to survive far more than the Victorian and South Australian populations.

In some Victorian locations, the koala populations have “bred well and have eaten themselves” out of habitat, stripping the trees bare. Management of these starving populations has been highly controversial and will not be part if this story, but suffice to say that translocaton of these populations, along with sterilisation of females and euthanasia of koalas has formed part of the management strategy. There have been suggestions that these koalas should be translocated to NSW and Qld where our koalas are rapidly disappearing.

Whilst this may appear to be a sensible suggestion sadly it is not. Both Victorian and South Australian koalas are much bigger than their counterparts in NSW and Qld and have much thicker fur. This is an example of clinal distribution where animals and plants have evolved and adapted to suit different climatic conditions. Both NSW and Qld koalas are much smaller, with finer fur and are adapted to survive in hotter climates. From this standpoint alone Victorian and South Australian koalas would not cope with our northern climate. Even though Victorian and South Australian koalas do get infected by chlamydia, it is generally felt that the strains “down south” are far less virulent than the strains in NSW and Qld. Therefore the southern koalas would more than likely be wiped out by the NSW and Qld chlamydial pathogens if they were translocated into NSW and Qld. This is without even going into the whole genetics debate!

What is the answer to this whole dilemma to reverse the decline of koalas?

There needs to be far better management strategies and tighter more robust legislation put in place by both the Federal and State governments to ensure their protection well into the future. There needs to be large amounts of quality undisturbed forested environments free of humans set aside where koalas can live undisturbed to breed and remain healthy.

Dog attacks – what wildlife personnel face

This area of wildlife work is arguably one of the most frustrating, emotional and preventable reasons for admission into care facilities. Education in regards to responsible pet ownership is important as is keeping good communication open with dog owners as difficult as it can be sometimes. Getting angry at the dog owner achieves nothing, as there is a great likelihood they will not contact wildlife care facilities in the future. Therefore education, a cool head and keeping the lines of communication open is the best defence wildlife personnel have until legislation changes to protect all wildlife on both private and public land from domestic dog attacks.

Unfortunately long term data suggests that a large percentage of admitted dog bite patients die as a result of their injuries – successful treatment and release of dog attack injury patients is quite low.

Those that work with treatment of these koalas often take it personally that they somehow “failed” if the koala dies. This is simply not true.

The number one reason for such a high death rate results from the crushing pressure of the dog’s jaws causing immediate major trauma to the skin and underlying muscle. Continual jaw pressure and shaking of the koala causes further trauma to the internal organs, resulting in their laceration, perforation and rupture. Many koalas simply bleed out. Lacerated intestinal tracts can cause peritonitis and organ failure. In the majority of cases death occurs within a matter of hours.

It is not unusual for a wildlife carer and or vet to be presented with a koala patient, who outwardly shows minimal to no visible injuries. Subtle signs such as matted saliva on the fur and/or one or two puncture wounds may hide what the Koala Hospital calls “the iceberg effect”.

What is the Iceberg Effect? This is where a koala looks to have suffered only minor injuries, such as one or two small puncture wounds. The casual observer often states “oh he/she looks fine, there was only one tiny wound”. The reality is that internally the koala may for example have crushing pressure injuries from the dog’s canines which cause massive trauma/haemorrhage to internal organs, tissues and muscle as described previously. So the tip of the Iceberg is the tiny external wound and the bulk of the iceberg is the massive trauma internally. This scenario is exactly the same with domestic cats who catch birds, small mammals and reptiles – minimal evidence of trauma on the outside of the body but internally it’s a mess and the majority die.

It is not unusual at post mortem of a dead dog attacked koala to find one or many of the following – major haemorrhage between skin and fascia wall (external musculature surrounding abdominal cavity, chest cavity and dorsal areas), penetration/perforated of the caecum and small bowel, torn liver, ruptured vena cava (major vessels to the kidneys), ruptured/torn ureters, laceration to the spleen and so on. Penetrating injuries or crush injuries to the chest cavity can collapse lungs and lacerate the pericardium. Dogs are quite capable of fracturing ribs, arm and leg bones and even skulls.

There are koalas that suffer major dog attack trauma and survive the initial wave. Sadly many often die some days or weeks later from infection in spite of the best veterinary care.

Post mortem work is critical to both allay the fears of those who feel they have failed in treating the injured koala and to learn what truly goes on internally. It is a very important education tool for those who work with wild koalas.

Nonetheless all is not lost as most koalas with true minor injuries do indeed respond and are successfully released.

Keeping a record of what breed of dog attacks koalas (and all wildlife) is an important tool for research purposes. These records are not designed to malign a particular breed but to bring awareness to what breeds are more likely to cause injuries. This information is helpful for potential new responsible dog owners who maybe seeking a suitable breed to own or to assist current owners on ways they can avoid harm in the future. Most dog owners are happy to come on board.

The Koala Hospital has collected this data for many years. The greatest percentage of dog attack injuries to koalas in coastal northern NSW are caused by the Staffordshire Bull Terrier. Does this data reflect that the people of this region prefer Staffies over other breeds? Or are Staffordshire Bull Terriers more likely to attack wildlife? As this breed is indeed an excellent family pet, could they just be “protective of their human pack”.

With koalas continually declining throughout Australia, deaths from being attacked by domestic dogs remains an incredibly frustrating scenario as each and every attack is actually preventable if the right measures are put in place. Interestingly research has shown that attacks on koalas by wild dogs is actually quite low (there are likely reasons why this is so).

What to do to prevent koalas being attacked by domestic dogs

  1. Choose a breed that is less likely to attack wildlife

  2. Plant trees in the front of a yard (not near powerlines) in preference to backyards

  3. If koala trees are in a backyard – try to fence off where the tree or trees are to keep dogs away. Erect timber runners from the tree to the fence to allow the koala to not have to go down to the ground

  4. Koalas often walk along the tops of fences to get from A to B. It is not unusual for a bigger dog to pull the koala off the fence and attack it. Try to house your dog in a fenced area that where koala will not visit.

  5. If possible lock dogs up at night

  6. Always have your dog on lead when out on public land

  7. Keep the Koala Hospital or other wildlife agency’s 24 hour emergency number handy and call immediately if your dog attacks a koala no matter what the time

  8. Where possible wrap the koala up in a big blanket to keep warm while waiting for responders

  9. Do not be fearful you will get “into trouble” – wildlife personnel simply wish to take the koala in for treatment

Greatest threats to Koalas
How you can get involved ‘hands on’