KOALA: CHARACTERISTICS, HABITAT, REPRODUCTION, FEEDING - BIOLOGY - 2025

The koala (Phascolarctos cinereus) is a placental mammal that is part of the Phascolarctidae family. It is found in eastern Australia, living in forests where eucalyptus plants abound, their main food.

The leaves of this plant species contain toxic substances, in addition to being a food source that provides a low energy level. Due to these characteristics, the koala, evolutionarily, has developed adaptations that allow it to digest said food and at the same time save energy.

Koala Source: Diliff

Morphologically, it has a strong jaw and a long colon compared to the size of its body. Also, it has a low metabolic rate and usually sleeps between 18 and 20 hours a day, thus reducing its energy consumption.

The size of this marsupial can vary between the populations that live north and those that inhabit the south of Australia, the latter being the largest. Its body is robust, with a broad face and a large nose. On the head the round ears stand out, from which some white locks emerge.

The color of its coat can range from gray to brown, for the upper part of the torso. In contrast, the belly is cream or white.

Cultural importance

The koala is part of the tradition and mythology of the indigenous Australians. In the Tharawa culture, the villagers believed that this marsupial helped to row the boat that took them to Australia.

Another myth relates that an aboriginal tribe killed a koala and used its long intestines to build a bridge. Thanks to it, people from other parts of the world could reach its territory.

There are several stories that tell how the koala lost its tail. One of these says that the kangaroo cuts it off, to punish him for being greedy and lazy.

The tribes that inhabited Victoria and Queensland regard him as an animal of immense wisdom, which is why they frequently sought his advice. According to the tradition of the indigenous people of Bidjara, this animal turned arid lands into lush forests.

The first Europeans who colonized Australia, considered the koala as lazy, with a threatening and fierce look. In the 20th century, his image took a positive turn, perhaps associated with his popularity and his inclusion in many children's stories.

characteristics

Vocalizations

To communicate, the Phascolarctos cinereus uses different sounds, which vary in pitch, intensity and frequency. The adult male emits loud bellows, consisting of a series of snoring-like inhalations and grunting-like exhalations.

Due to their low frequency, these vocalizations can travel long distances. Thus, the groups that are separated can exchange information about possible threats or regarding the reproductive period.

In relation to this, males usually roar especially at the time of mating, to attract females and to intimidate males who try to approach their group. Likewise, they shout to inform the other members of the community that they have moved to a new tree.

These sounds are particular to each animal, characterizing it in such a way that it differentiates it from the rest of the group. Females scream, growl and wail when in danger and need to defend themselves.

Young people scream when they have a problem. As they age, this sound becomes a squawk and is used to express both anxiety and aggression.

Gestures

While vocalizing, the koala makes various expressions with its face. When it moans, howls or growls, the marsupial places its ears forward and curls its upper lip.

On the contrary, in the screams, the ears move back and the lips contract. Females, when upset, bring their lips together and lift their ears.

Size

There is a difference between the size of the koalas that live north of Australia and those that inhabit the south. The latter are usually the largest and heaviest. In both cases, there is a very marked sexual dimorphism, since the males are much larger than the females.

Thus, in the south, the male weighs 11.8 kilograms and measures 78 centimeters, while the female has a length of 72 centimeters, weighing 7.9 kilograms.

In relation to those located to the north, the male reaches an average height of 70 centimeters, with a weight of 6.5 kilograms. The female is 69 centimeters long and weighs around 5 kilograms.

Fur

The Phascolarctos cinereus has a dense, woolly coat. However, those who live in northern Australia may have it light and short. In the area of ​​the back, the hair can be thick and longer than on the belly. In relation to the ears, the fur is thick both on the outside and inside.

Thanks to these characteristics, the coat works as a protector from extreme temperatures, both high and low. In addition, it has a "waterproof" effect, since it repels water, preventing the animal from getting wet in the rainy season.

Coloration

Color may also vary depending on geographic location. Those who live in the south are usually darker in shades. In general, the upper part of its body can be from a gray to a brown hue, while the belly is white.

The rump has white spots and on the edge of the ears there are long hairs of the same color. In relation to the chin, the inner side of the front legs and the chest, they are white.

In mature males, the scent gland that they have on the chest stands out, since it has a brown color. This, when rubbed on a surface such as tree bark, emits an unpleasant odor. Thus, the koala tries to scare off other males or possible predators.

Extremities

The strong and long limbs, together with a long, muscular body, allow the koala to support its own weight while climbing.

The strength that the Phascolarctos cinereus has to climb trees comes, in large part, from the musculature of the thigh. This joins the tibia in a lower area than in other mammals.

Likewise, the hind legs and the fore legs have a very similar length. These have rough pads and sharp claws, which facilitate grip on branches and trunks.

On each leg there are five fingers. In the previous ones, two of these are opposed to the rest, which allows the animal a more secure grip.

The hind legs do not have opposite digits. However, the second and third toes are fused, forming one, but with two claws. This is used for cleaning, including removing ticks.

Brain

The surface of this organ is smooth and has fewer folds than the rest of its kind. Compared to body weight, the brain of this marsupial is relatively small, weighing 19.2 grams. This could be an adaptation to the energy restrictions of your diet.

Sensory organs

The nose is large and covered with leathery skin. In this animal, the sense of smell is of utmost importance, since it allows you to differentiate the degree of toxin in the eucalyptus leaves. In addition, you can also smell the marks that other koalas leave on the trees.

Specialists maintain that, from birth, this species already has a keen sense of smell. Thus, the newborn baby can be guided by the smell of mother's milk and reach the mother's pouch.

Its ears are round and large, which helps it pick up sounds that are at a distance. Thus, you can communicate with other populations that are far away.

The eyes are small and have vertical pupils, unlike the rest of the marsupials, which have them horizontal. The vision of Phascolarctos cinereus is not very developed.

Koalas have a special structure in the speech apparatus, which is located in the soft palate. It is known as the velar vocal cords. They emit sounds of a low pitch, imperceptible to the human ear.

Dentition

The dentition of this species consists of incisors and several cheek teeth. These are a premolar and four molars, which are separated from each other. The molars crush the fibrous eucalyptus leaves into small particles.

This is beneficial for more efficient stomach digestion and intestinal absorption.

Tail

The koala lacks a visible outer tail, unlike the other arboreal marsupials. However, in its skeletal system there are vertebrae that are associated with a tail. In this way, it is assumed that, at some point in its evolution, the koala had a visible tail.

Marsupio

The pouch is a bag of skin, generally located at the abdominal level. This covers the breasts and has the function of incubating and suckling the newborn baby, since at this stage of its life it is very underdeveloped.

In the koala, this bag is rear-facing. However, the young do not fall off while the mother climbs the trees. This is due to the sphincter muscle at the opening of the bursa, which closes as it rises. In this way, young people are protected.

Milk

In mammals, milk production is a very important aspect. The koala has a short gestation period, but nevertheless the lactation stage is quite long.

Since, at birth, the offspring lack the ability to cope with infectious agents, they depend on mother's milk to develop adequate immune protection.

Some researchers performed an analysis on the milk, identifying some proteins, such as lactotransferrin, immunoglobulins and β-lactoglobulin. Likewise, this liquid has numerous antimicrobial peptides.

Some sequences corresponding to retroviruses were also identified, thus identifying the possible transmission of these, from the mother to the offspring.

Evolutionary origin

In recent decades, a large number of fossils have been discovered, accounting for around 18 extinct species. This may indicate that koalas existed in abundance in the past.

The teeth in these records suggest that their diet was similar to that of modern species. In addition, like current marsupials, they had developed auditory structures. This could be associated with the use of vocalizations to communicate.

Abundance and extinctions

During the Oligocene and Miocene times, koalas lived in tropical rainforests and their diet was not very specialized. According to the climate it became dry, around the Miocene, the tropical forests were diminishing, thus allowing the expansion of eucalyptus forests.

Thanks to this, the marsupials were able to expand and their population increased. A continuing drought trend could create the opposite effect, causing some species to disappear, as occurred in southwestern western Australia during the late Pleistocene.

Another hypothesis about the extinctions of the Phascolarctos cinereus coincides with the arrival of humans in Australia, who hunted and altered the natural habitat of the animal.

Although these theories could be difficult to verify, it is highly probable that climatic variations and human activity affected, in primitive times, the distribution of the koala.

Ramifications

The ancestors of the Vombatiformes, a suborder to which the koala belongs, were most likely arboreal animals. Of this group, the koala lineage was possibly the first to split, around 40 million years ago, in the Eocene.

As for the genus Phascolarctos, it was divided from the Litokoala during the late Miocene. At that time, the members of this clade underwent various adaptations, which made it easier for them to live on a diet based on eucalyptus.

Among the specializations is that of the palate, which has moved towards the frontal area of ​​the skull. Also, the premolars and molars became larger and the distance between the incisors and the molars increased.

Some researchers suggest that Phascolarctos cinereus may have emerged as a smaller species of P. stirtoni. This could be supported by the fact that in the late Pleistocene some large mammals reduced their size.

However, recent studies question this hypothesis. This is because they consider that P. stirtoni and P. cinereus were sympatric in the middle and late Pleistocene, and possibly in the Pliocene.

Variations

Traditionally, the existence of the subspecies P. c. Adustus, P. c. Cinereus and P. c. Victor. Among these there are differences in terms of the thickness and color of the coat, the bony characteristics of the skull and the size. However, its classification as a subspecies is under discussion.

Genetic studies suggest that these variations are associated with populations that have differentiated, with a limited genetic flow between them. Furthermore, the results suggest that the subspecies form a single unit, of evolutionary significance.

Other investigations suggest that the populations of this marsupial present low genetic variation and a high level of inbreeding. The little diversity at the genetic level could be present in these groups since the late Pleistocene.

Likewise, some barriers, such as rivers, roads or cities, can limit gene flow, contributing to genetic differentiation.

Habitat and distribution

The koala is widely distributed in Australia, especially in the east of that country. Its geographical range covers around 1,000,000 km2 and 30 ecoregions. Thus, it extends to the northeast, southeast and central Queensland, in the eastern region of the state of New South Wales, in Victoria and southeast of South Australia. It is not found in Tasmania or Western Australia.

This species was introduced near the coastal city of Adelaide and on various islands, such as the French Island, Phillip and Kangaroo. It has also been introduced in the Adelaide region. Those that inhabit the Magnetic Island represent the northern limit of its distribution.

In Queensland, Phascolarctos cinereus are scattered, being numerous in the southeast of the state. In New South Wales, they live only in Pilliga, while in Victoria they live in almost all regions.

In relation to South Australia, in 1920 they became extinct, being later reintroduced to that territory.

Habitat

The koala's habitat is very wide. It can range from open woodlands to riparian regions, which offer refuge in periods of extreme heat and drought. Likewise, it is found in temperate, tropical and semi arid climates.

Reproduction

The female of the Phascolarctos cinereus reaches sexual maturity around two or three years. The male is fertile at two years, but generally begins mating at four. This is because the competition for a female requires a size much larger than this.

As in the vast majority of marsupials, the male has a forked penis, the sheath of which contains some natural bacteria. They play an important role in the fertilization process.

The female has 2 separate uteri and 2 lateral vaginas. In addition, in the pouch it has two nipples, with which it will suckle the baby.

Females are characterized by being seasonal polyesters, whose estrous cycle could last between 27 and 30 days. Generally its reproduction is annual and usually occurs in the autumn and summer months. However, there may be variations related to the abundance of food.

Courtship

When the female is in heat, she keeps her head up higher than normal, and her body often shows tremors. However, sometimes males do not recognize these signals and seek to copulate with others that are not in heat.

Males emit vocalizations to attract females. These are usually short low-pitched bellows, followed by inhalations.

Because the male is larger, he can subdue the female from behind, causing her to fall to the ground many times. The female could fight and scream against the males, although she tends to bow to the more dominant one.

This situation attracts other males, which leads to fighting between them. These fights allow the female to choose with whom to mate. Taking into account that each male has her own bellow, the female can easily locate her within the group.

Breeding

After 25 to 35 days, the time that gestation lasts, the female gives birth to a calf, although occasionally she may have twins. The baby is born without having completed its embryonic stage, thus weighing about 0.5 grams.

However, the newborn has lips and limbs. In addition, the urinary, respiratory, and digestive systems are active. At birth, the calf rises up to the pouch, immediately attaching itself to a nipple. It remains there for 6 to 8 months, developing and growing.

Around the sixth month, the mother begins to prepare the young for his eucalyptus-based diet. For this, it predgests the leaves and produces a fecal slurry, which the baby eats from the cloaca.

This material has a different composition than feces, more similar to that of the caecum, with an abundance of bacteria. This food, supplied by the mother, provides the young man with a complementary source of protein.

When it emerges from the bag, the baby weighs between 300 and 500 grams. It begins to eat leaves and is located on the back of the mother, who carries it until it is approximately one year old. After this time, the koala becomes independent and moves away from the mother.

Feeding

The koala feeds almost exclusively on the leaves of eucalyptus, a very abundant plant species in Australia. Although there are more than 600 species, these marsupials eat around 20 varieties. Some of these are Eucalyptus viminalis, E. camaldulensis, E. ovata, E. punctata, and E. tereticornis.

However, they can also consume leaves from other genera, such as Callitris, Acacia, Leptospermum, Allocasuarina, and Melaleuca.

Eucalyptus leaves are difficult to digest, low in protein and toxic to most organisms. The main benefit that eucalyptus gives to Phascolarctos cinereus is that there is no food competition with other species. However, this mammal, evolutionarily, had to make several adaptations to consume them.

Adaptations

Your stomach contains bacteria capable of metabolizing toxins from the leaves. These produce cytochrome P450, which acts on the toxic substance, breaking it down in the liver.

Likewise, thanks to their powerful jaw and grooved teeth, they can cut the leaves into very small pieces, starting the digestive process. Also, the koala is a hindgut fermenter and has a large caecum, in proportion to its body.

This allows it to selectively retain and ferment part of its food. Also, it facilitates the action of symbiotic bacteria, in the degradation of tannins and other toxic elements that abound in eucalyptus.

In addition to this, the marsupial has a low metabolic rate, since they sleep around 18 hours a day and their brain is small. All this makes it save energy, conserving it.

One way to preserve water is that your stool is relatively dry and you can store lots of water in the cecum.

Behavior

Koalas are arboreal animals and have nocturnal habits. They descend from trees almost exclusively to move to another tree. Also, once on the ground, they lick it to take particles and consume them. These will contribute to the crushing process of the tough and fibrous eucalyptus leaf.

They are solitary, except in the reproductive season, where the male may form a small harem. Phascolarctos cinereus prefer to avoid any aggressive behavior, because with them they lose energy. However, they tend to have some agonistic behaviors.

On occasion, between males, they can chase, bite, and fight each other. Some of them can even try to move the rival from the tree. For this, you can take it by the shoulders and bite it several times. When the animal is expelled, the winner groans and marks the tree with his scent.

With regard to the regulation of body temperature, these marsupials make changes in their postures. For example, on hot days, they extend their limbs, which hang down on the sides of the branch.

Conversely, when the weather is cold, wet, or windy, koalas cross their arms against their chests and stretch their paws against their belly.

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