Koala

Koalas (Phascolarctos cinereus) are arboreal marsupials characterized by a grayish-brown furry body, fuzzy ears, and a broad, dark nose. They are often mistakenly referred to as koala bears, even though they are not bears at all. In reality, their closest relatives are wombats.

This species is native to Australia, where it inhabits woodlands and open forests. It spends most of the day sleeping in trees, sometimes for as long as 20 hours, and becomes active at night to forage. As a strict herbivore, it specializes in the leaves of eucalyptus trees. Although these leaves are highly toxic, koalas are hindgut fermenters with a specialized digestive system that enables them to digest the leaves.

These docile, harmless animals face serious threats to their survival and are listed as Vulnerable (VU) in the IUCN Red List of Threatened Species.

Subspecies

There are 3 recognized subspecies of koalas.

• The Queensland koala (Phascolarctos cinereus adustus)
• The New South Wales koala (Phascolarctos cinereus cinereus) 
• The Victorian koala (Phascolarctos cinereus victor)

Description

Size: Length: 24 to 33 in (60 to 85 cm)

Weight: Between 8.8 and 33.1 lb (4 and 15 kg). Males of some populations are about 50% heavier than females.

Body and Coloration:  Koalas are easily identified by their large heads, furry ears, and broad black noses. 

They are typically grayish-brown in color, with white fur on their belly, chest, inner arms, and ears. The fur on their rump is usually darker than on any other part of the body. Although the fur appears soft, it is coarse in texture, similar to that of sheep.

The upper part of a koala’s body is short and muscular, equipped with long forelimbs that aid in climbing trees. It also has sharp claws on all four limbs, which help the animal grip the branches firmly.

Their front paws are large and equipped with two opposable digits (first and second) for gripping branches. In contrast, the second and third toes of their back paws are fused and function as a comb, which the koala uses to groom its fur.

Their eyes are relatively small and, unlike most other marsupials, have pupils shaped like vertical slits. This feature helps them see clearly as they climb on vertical surfaces, like tree trunks.

Male koalas have more curved noses than females, and they also have a specialized chest gland (visible as bald patches), which the females do not have. These chest glands release secretions that help in territory marking. As marsupials, female koalas bear a pouch or marsupium for carrying their babies.

Distribution

This species is found along the eastern and southeastern coasts, including New South Wales, Queensland, Victoria, and South Australia. It has been introduced to several nearby islands, including Magnetic Island, which represents its northern limit.

Fossil records suggest that koalas were once found in Western Australia. However, they probably went extinct due to climatic changes in the region, as well as overhunting by Indigenous Australians. To help revive its population in this region, the species was introduced to Western Australia at Yanchep in 1938. However, by 2022, its numbers had declined to just a few individuals.

Habitat

They inhabit woodlands and open forests replete with eucalyptus trees, the leaves of which constitute most of their diet. In semi-arid regions, they prefer living near rivers, streams, and creeks (riparian zones) with relatively high vegetation density.

Diet

Koalas are obligate herbivores that typically feed on the leaves of eucalyptus (Eucalyptus). In fact, they can eat as much as a pound of eucalyptus leaves per day.

Of over 600 species of Eucalyptus in Australia, they prefer feeding on only around 30 species. On average, E. microcorys, E. tereticornis, and E. camaldulensis account for over 20% of their diet. However, they occasionally feed on leaves of other genera of trees, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca.

They do not need to drink often as they obtain enough hydration from the leaves that they consume.

Behavior

• Due to their low-energy diet, koalas sleep for as much as 20 hours daily. They typically forage at night and tend to eat and sleep in the same tree. However, they descend to the ground to move from one tree to another.
• Koalas often sit crouched on the fork of a tree, grasping the branches with their forelimbs. They then grab the leaves with one forepaw and pull them toward their mouth. These animals typically feed in four to six sessions every day, consuming up to 400 g (14 oz) of leaves daily.
• On warm days, koalas often rest with their back against a branch or lie with their limbs dangling to release excess heat. If the temperature rises unbearably, they move lower in the tree canopy and rest close to the trunk, where the surface remains considerably cooler. In contrast, during wetter conditions, they curl up tightly to stay warm.
• These marsupials are typically asocial and prefer to live alone without much interaction among themselves. Their populations are composed of resident females and males who move around. When a male koala climbs a tree, he rubs his chest against the bark to leave his scent, marking his presence in the area. Other individuals then sniff the marked bark to detect the male’s presence.
• Male koalas typically communicate by producing deep bellows, especially during the breeding season. Females also bellow, though much more softly than males, and may produce additional vocalizations such as snarls, wails, and screams. 
• When one koala tries to outcompete another while moving from one branch to another, they may quarrel by biting each other. If this happens with strangers, the fight becomes intense, typically involving wrestling and chasing.

Lifespan

The koala has an average lifespan of 13 to 18 years in the wild. However, under optimal conditions, it may live longer, up to 20 years, in captivity.

Reproduction and Life Cycle

Koalas typically breed seasonally every year, with most births occurring between October and May. The males emit bellowing calls to attract the females, with larger males typically getting more female attention. These males fight with each other for access to the females, using their claws to attack each other. Once the female selects the most dominant male, the pair mates.

During copulation, the female undergoes ovulation, releasing an egg, which is eventually fertilized internally by the male. After a gestation period of 33 to 35 days, the female gives birth to one (or occasionally two) young called a joey. The joey is underdeveloped at birth (altricial) and typically weighs less than a gram. However, it has relatively well-developed lips, forelimbs, and shoulders, and it can breathe, urinate, and defecate independently.

The joey crawls into the mother’s pouch, attaches to one of the two teats, and suckles on it. At about 7 weeks, it has a large head, clear facial edges, more coloration on its body, and, depending on the species, a visible pouch (in females) or scrotum (in males). By 13 weeks, the joey weighs about 50 g (1.8 oz), its head has doubled in size, its body is covered in hair, and its eyes begin to open. At 26 weeks, it becomes even furrier and starts peeking out of the pouch.

When the joey is about 6 or 7 months old, it weighs between 300 and 500 g (11 and 18 oz) and emerges from the pouch. Around this stage, the mother prepares the baby for a folivorous diet by producing a fecal pap (a special nutrient-rich form of feces), which the baby consumes directly from the mother’s cloaca. At about 9 months, the joey attains adult coat color and rides on its mother’s back, slowly learning to climb trees. Gradually, as it becomes big enough, weighing around 2.5 kg (5.5 lb), the mother weans it off, though she remains around the baby until it is about 2 years old.

While females attain sexual maturity at around 3 years, males become sexually mature when they are about 4 years old.

Predators

Since koalas live safely on top of trees, they have few natural predators. Nonetheless, they are killed by pythons and dingos when they descend to the ground. Juvenile koalas are attacked by some birds of prey, including wedge-tailed eagles and hawks.

Adaptations

• Since eucalyptus leaves are fibrous and rich in cellulose, most digestion occurs in the caecum and colon (the hindgut), where symbiotic bacteria act on the ingested food. Their caecum is about 200 cm (79 in) long and 10 cm (3.9 in) wide, which allows slow, extended fermentation of the food. This digestive retention lasts about 100 hours in the wild and 200 hours in captivity.
• Adult koalas, at their most active stage, have partially worn molars, which efficiently grind eucalyptus leaves into finer, easily digestible bits. Moreover, these animals may regurgitate their food to chew it a second time, aiding in further breakdown and nutrient absorption in the small intestine.
• Koalas produce cytochrome P450 enzymes in the liver, which help digest the toxic plant secondary metabolites, phenolic compounds, and terpenes found in eucalyptus leaves.

Conservation Status

As of the 2014 assessment, the koala is listed as Vulnerable (VU) in the IUCN Red List of Threatened Species. In February 2022, populations of koalas in Queensland, New South Wales, and the Australian Capital Territory were listed as endangered by the Australian government.

Factors like poaching, habitat destruction, and climate change lead to a constant decline in the number of koalas. Also, certain diseases, like chlamydia and Koala Retrovirus (KoRV), lower their survival and reproduction rates.

According to the International Fund for Animal Welfare (IFAW), between 100,000 and 500,000 koalas remain in the wild. However, to help reduce further population loss, conservation efforts, like sanctuaries and national parks, are constantly underway. Additionally, captive breeding programs and disease management initiatives support the survival of this animal in the wild.

Interesting Facts

1. Since eucalyptus leaves are low in calories and provide less energy, koalas have a remarkably low metabolic rate, about 50% of what is typical for mammals of their size.
2. The brain of a koala is about 60% smaller than that of other marsupials of similar size, weighing only around 19.2 g (0.68 oz). It does not even fill the cranial cavity and is surrounded by large amounts of cerebrospinal fluid, which likely helps protect the brain if the animal falls from a tree.