Do Koalas Have Lungs? Explaining Their Respiratory System

Koalas absolutely have lungs, and they use them to breathe air just like every other mammal on the planet. As marsupials, koalas share the same fundamental respiratory blueprint found in dogs, horses, and humans: air enters through the nose, passes down the trachea, and fills a pair of lungs where oxygen moves into the bloodstream and carbon dioxide moves out. What makes the koala respiratory system interesting is not whether lungs exist but how those lungs operate under unusual conditions. Koalas breathe remarkably slowly, cope with a steady stream of volatile plant toxins in every breath, and possess vocal structures in their airway found in no other land mammal.

Why the Question Comes Up

Nobody asks whether a horse or a cat has lungs. The question tends to surface for koalas because they sit at the intersection of several pieces of popular confusion. They are often mistakenly called “koala bears,” which can blur the line between marsupials and other animal groups for people who are fuzzy on the categories. They spend most of the day motionless, sometimes appearing almost lifeless in a tree fork, which makes casual observers wonder how their bodies even function. And their diet of tough, toxic eucalyptus leaves is so unusual that it invites questions about whether their internal organs differ from those of more familiar animals. The short answer is that koala organs are recognizably mammalian. The longer answer is that several features of their respiratory system have been fine-tuned by evolution to suit a very particular lifestyle.

A Slow and Efficient Breathing Rate

Koalas are among the most sedentary mammals alive. They sleep or rest for roughly eighteen to twenty hours a day, and even their waking hours are spent mostly sitting still, chewing leaves. This low-energy existence is reflected in their breathing. A healthy, resting koala takes only about ten to fifteen breaths per minute, which veterinary researchers treat as the normal baseline range for the species.¹ For comparison, a resting adult human breathes about twelve to twenty times per minute, and a similarly sized dog can breathe even faster. The koala sits at the low end of what you would expect for any mammal its size.

This leisurely breathing rate connects directly to the koala’s metabolic strategy. Eucalyptus leaves are low in calories and high in fiber and toxins, so koalas conserve energy at every opportunity. A lower metabolic rate means the tissues demand less oxygen per minute, so the lungs do not need to cycle air as rapidly. The result is an animal that can survive on a diet most other mammals would starve on, partly because its respiratory and metabolic systems are tuned to extract value from very little fuel.

Breathing Through a Cloud of Plant Toxins

Eucalyptus leaves contain high concentrations of volatile organic compounds called monoterpenes. The two most prominent are 1,8-cineole (the chemical responsible for that sharp, medicinal eucalyptus smell) and p-cymene. Koalas encounter these compounds not only in the leaves they chew and swallow but also in the air around them. Eucalyptus forests release monoterpenes into the atmosphere continuously, and koalas spend their lives immersed in this chemical haze. Every breath a koala takes carries some of these molecules into the airways and down to the lungs.

Most of the heavy lifting for detoxifying eucalyptus toxins happens in the liver, where specialized enzymes break down the compounds after they are absorbed through the gut. But the respiratory tract is the first tissue to make contact with airborne monoterpenes, and researchers have looked at what that exposure does to the immune cells lining the airways. In laboratory experiments, koala immune cells exposed to 1,8-cineole and p-cymene showed dose-dependent reductions in the expression of several inflammatory signaling molecules, without the cells themselves being killed off.² In plain terms, the monoterpenes dialed down the immune alarm signals that cells would normally produce in response to infection or irritation.

That finding has a double edge. On one hand, it may help explain why koalas tolerate breathing eucalyptus vapor day in and day out without constant airway inflammation. A dampened inflammatory response to these specific chemicals could be protective, preventing the lungs from reacting to something that is, for a koala, simply the background air. On the other hand, suppressed immune signaling in the respiratory tract could make koalas more vulnerable to actual infections. Researchers suspect this immunosuppressive effect may be one reason koalas are so susceptible to diseases like chlamydia, which thrives when the host’s immune defenses are weakened.

A Unique Vocal Apparatus Inside the Airway

One of the most unusual features of the koala respiratory tract has nothing to do with gas exchange. Male koalas produce a deep, resonant bellow during the breeding season that sounds startlingly like a large animal, far bigger than the roughly ten-kilogram marsupial making the noise. For years, researchers were puzzled by how such a small creature generated sounds at frequencies more typical of an elephant-sized mammal. The answer turned out to be a set of anatomical structures found nowhere else among land-dwelling mammals.

Detailed anatomical work on the koala’s soft palate revealed a pair of fleshy folds called velar vocal folds, positioned at the back of the oral cavity where it meets the throat. These folds narrow the opening between the mouth and the laryngopharynx down to a slit-like passage, and they protrude downward into the airway.³ When a male koala bellows, he forces air past these extra folds in addition to the standard laryngeal vocal folds that all mammals share. The velar vocal folds vibrate at very low frequencies, generating the basso profundo rumble that carries through the eucalyptus forest at night.

The bellows serve a social purpose. Free-ranging males adjust their calling behavior based on the apparent size of a rival. When researchers played back artificially modified calls that simulated a larger male, the listening koalas spent more time bellowing and produced longer calls in response, though they also took longer to start calling, as if sizing up the situation before committing to a vocal contest.⁴ The formant frequencies in a bellow, which are shaped by the length of the vocal tract and the configuration of those extra folds, give other koalas information about the caller’s body size. Bigger males produce lower-pitched formants, and rivals clearly pay attention to the difference.

The practical upshot is that the koala airway pulls double duty. It handles routine gas exchange, quietly moving air in and out of the lungs at that low resting rate, and it also functions as a surprisingly powerful sound-production system. The velar vocal folds are a reminder that respiratory anatomy can be shaped by sexual selection as much as by the demands of oxygen delivery.

Respiratory Diseases That Plague Koalas

Koala lungs face a heavier disease burden than you might expect for a wild animal. Several infections target the respiratory system either directly or as part of a wider assault on the body, and some of these diseases have become serious conservation concerns.

Chlamydia is the most widely discussed. While it is best known for causing eye and urogenital infections in koalas, chlamydial bacteria can also affect the respiratory tract. The koala biovar of Chlamydia pneumoniae, a relative of the chlamydia strains that cause pneumonia in humans, has been shown to infect both koala and human immune cells in laboratory conditions, producing large bacterial inclusions inside the cells.⁵ Respiratory chlamydial infection can lead to pneumonia and chronic airway disease in affected koalas, and because chlamydia spreads readily through koala populations, entire colonies can be affected.

Koala retrovirus, or KoRV, adds another layer of vulnerability. This virus has integrated itself into the koala genome and is passed from parent to offspring as well as spreading between individuals. Research has linked non-baseline subtypes of KoRV, along with higher levels of the virus circulating in the blood, to increased rates of leukemia, lymphoma, and other cancers in koalas.⁶ While KoRV does not target the lungs specifically, the immunosuppression it causes can make koalas less able to fight off respiratory infections. A koala carrying a heavy KoRV burden and exposed to chlamydia faces a compounded risk where each condition worsens the other.

Together, these infections interact with the immunosuppressive effects of eucalyptus monoterpenes described earlier to create a population that is unusually fragile when it comes to respiratory health. Conservation biologists tracking koala decline often point to disease as one of the leading threats, alongside habitat loss and vehicle strikes.

What Bushfire Smoke Does to Koala Lungs

Australia’s increasingly severe bushfire seasons have added yet another respiratory threat. Koalas are slow-moving, arboreal animals with limited ability to flee fast-moving fire, so many are caught in or near the burn zone. Those that survive the flames often inhale large quantities of smoke, and the damage to their lungs can be devastating even when external burns are minor.

A pathology study of koalas affected by bushfire found diffuse damage throughout the lungs. The tiny air sacs where gas exchange occurs were congested with blood and flooded with protein-rich fluid, indicating that the delicate lung lining had been breached and blood vessels were leaking. Inside the air sacs, immune cells called alveolar macrophages contained foamy cytoplasm and brown particles consistent with soot, evidence that the lungs had been trying to clean inhaled smoke particles but were overwhelmed.⁷ The trachea appeared relatively normal, but soot particles were found in its lumen, confirming that the animals had been breathing smoke-laden air.

This type of lung injury, where fluid fills the alveoli and the tissue becomes inflamed, is similar to what firefighters and wildfire survivors experience. In a koala that is already immunocompromised by KoRV or chlamydia, smoke inhalation can tip the balance from a survivable event to a fatal one. Wildlife hospitals that treat bushfire-rescued koalas report that respiratory complications are among the most common reasons animals fail to recover, even when their skin burns have healed. Oxygen supplementation, fluid management, and anti-inflammatory treatment are part of the standard care protocol, but the prognosis for severe inhalation injury remains poor.

Monitoring Breathing Under Veterinary Care

Because koalas are increasingly brought into veterinary settings for disease treatment, bushfire rehabilitation, and research-related health checks, understanding what normal koala breathing looks like has real practical importance. The resting respiratory rate of ten to fifteen breaths per minute serves as the clinical baseline, and deviations from that range alert veterinarians to problems. A koala breathing significantly faster than fifteen breaths per minute at rest may be in pain, running a fever, or developing pneumonia.

Sedation and anesthesia pose particular challenges for koala lungs. In a field study comparing two drug protocols for immobilizing free-ranging koalas, one combination produced a significant spike in breathing rate, with animals averaging around 67 breaths per minute under sedation, more than four times the normal resting rate.¹ That kind of rapid, shallow breathing can impair the lungs’ ability to exchange gases efficiently and adds stress to an already compromised system. Choosing the right anesthetic protocol for koalas is therefore not a trivial decision; the wrong drug combination can turn a routine capture into a respiratory emergency.

Veterinary teams working with koalas in the field or in hospitals monitor breathing rate, blood oxygen saturation, and heart rate together to get a picture of how the respiratory system is coping. The low baseline metabolic rate that makes koalas such energy misers in the wild also means they have a relatively narrow margin of respiratory reserve. An animal that has to ramp up breathing quickly, whether because of smoke inhalation, disease, or the stress of being handled, can run into trouble faster than a more metabolically active mammal might.

How Koala Lungs Compare to Other Marsupials

Koalas belong to the order Diprotodontia, which also includes wombats, kangaroos, and possums. All of these animals have paired lungs, a diaphragm, and the same basic airway architecture. Where koalas stand out is in the degree to which their respiratory system has been shaped by their niche. Kangaroos, for instance, are active, fast-moving animals with higher metabolic demands and breathing rates that climb steeply during locomotion. Wombats are burrowers that breathe air with lower oxygen concentrations underground. Each marsupial lineage has tweaked the shared respiratory template to fit its lifestyle.

The koala’s tweaks are less about structural novelty in the lungs themselves and more about the supporting cast. The liver’s extraordinary capacity to neutralize plant toxins, the velar vocal folds that repurpose the upper airway for sound production, the immune cells that appear partially tolerant of inhaled monoterpenes: these surrounding adaptations are what make koala respiration distinctive. The lungs do the same job they do in any mammal, but they operate in an environment, both chemical and ecological, that is remarkably different from most.

Marsupials in general also tend to have slightly lower basal metabolic rates than similarly sized placental mammals, which means their oxygen consumption per unit of body weight is a little lower across the board. Koalas sit at the extreme end of even the marsupial spectrum. Their entire physiology seems oriented around doing as little as possible, as efficiently as possible, and the lungs are no exception. They are built not for peak performance but for quiet, sustained, low-cost operation in a treetop canopy saturated with volatile chemicals.