A eucalyptus-loving marsupial under threat
What does it look like?
The Koala is one of our most widely recognised and best-loved native animals. It has soft fur ranging from grey to brown on its back and sides, with white fur on its belly. It has large grey-white furry ears, a prominent black nose and no tail.
Its distinctively solid body, topped with fluffy ears, gives the impression that the koala is rather cuddly. In fact, it has strong muscles and huge claws which it uses to climb to the top of tall eucalyptus trees. The Koala is commonly called a ‘Koala bear’ because its stocky, furry physique often reminds people of a bear. However, it is actually a marsupial, and it belongs to the same order as kangaroos and possums.
On each front paw, the koala has two thumbs and three fingers, giving them a strong grip around wide tree trunks. Their muscular hind legs have a clawless big toe, as well as two hind toes that are fused into one. This special digit is used like a comb, keeping their soft fur free from knots, dirt and ticks.
Adult male Koalas weigh 6 - 12 kg and adult females weigh 5 - 8 kg. The largest Koalas weigh over 10 kilograms and are found in Victoria, while the smallest live in North Queensland and weigh only 5.5 kilograms.
Koalas live for between 10 and 20 years.
Where does it live?
Koalas love eucalypt woodlands and forests. They spend most of their time in trees, only coming to the ground to move to the next tree trunk. By day, they can often be seen sleeping, nestled snugly into the fork of two tree branches. But at night, the Koala is much more active. It feeds enthusiastically on the leaves, shoots and stems of more than 70 species of eucalypts, and 30 non-eucalypt species. In one area, the Koala may choose a preferred species of tree and feed almost exclusively on this species.
A Koala will have a home range that can vary enormously. If the number and range of food trees is high, then their range may be only 2 hectares. However, if they need to roam further to get to their preferred tree species, their home range may be up to several hundred hectares in size.
Koalas in the Sydney region – a story of dramatic decline
The Koala was once common throughout eastern Australia. But sadly, a number of factors – including the fur trade, urban development and disease - have led to a massive reduction in its numbers. They are now found in fragmented pockets of south-eastern Australia and Queensland, and only where there are food trees to sustain them. However, there have been successful efforts to re-introduce the Koala to parts of Victoria and South Australia.
Koalas are found widely in New South Wales, but most commonly on the central and north coasts. Around Sydney, you can find sparse populations of Koalas in the following regions:
- Hornsby Plateau
- Ku-ring-gai Chase National Park
- Woronora Plateau
Koalas in Pittwater – once abundant, now almost gone
In Pittwater and Warringah, Koalas were once common and widespread. They were particularly numerous on Barrenjoey Peninsula. From the 1940’s to the 1970’s, the Koala colony on Barrenjoey Peninsula was the largest and best known colony in the Sydney region.
- In the 1950s, the size of the population on Barrenjoey Peninsula was estimated at about 120, with evidence of breeding and no signs of disease. Koalas were also reported during the 1950’s at Mona Vale and Warriewood, and at Cottage Point in Ku-ring-gai Chase National Park.
- In the 1960s, Koalas were reported at Mona Vale, Bayview, Elanora Heights, Elvina Bay, Great Mackerel Beach and other localities in Ku-ring-gai Chase National Park. They were regularly seen throughout the Peninsula, and were even reported to be on Barrenjoey Head in 1967.
- In 1970, the population on Barrenjoey Peninsula was estimated to be over 123 Koalas, distributed from Palm Beach to Mona Vale, with the greatest numbers in the Avalon-Clareville area.
- By 1989, however, the population had been reduced to only about eight animals.
- In 1993, a study estimated the population at only four to six animals. There may be even fewer animals now.
- The most frequents sightings of Koalas over the past 12 years have been in Avalon, where there is still an existing population.
- A further survey conducted by the University of Western Sydney with the National Parks and Wildlife Service in 2003 found no animals at all. It is likely that the Koala population on Barrenjoey Peninsula remains in serious decline.
Sadly, in Pittwater you will not see a Koala in the wild. However, there are still small populations in Ku-ring-gai Chase National Park, and possibly also in Garigal National Park. These populations are isolated from each other by the density of urban development and the lack of bushland corridors.
What does it eat?
Few people would think of the Koala without thinking of gum trees too – and with good reason! The Koala has an unusual diet; they feed exclusively on the foliage of certain eucalyptus trees, specifically trees belonging to the following genera:
Koalas are highly selective about their food trees; studies have shown that Koalas will focus on one or two locally available eucalypt species. They may even select a favorite tree, returning again and again to feed on its foliage. Even within one area, species that are favoured food trees in some situations may be less favoured when growing on different soils or landscapes. So it is important to know as much as possible about the Koala’s specific food preferences in each region. The more we know, the better we can protect and preserve their food trees.
If necessary, the Koala will also feed on the foliage of other eucalypt species and other types of trees, including non-native trees.
After spending their nights feeding on up to half a kilogram of leaves, the Koala will spend most the day sleeping. Curled tightly in the fork of two branches, it conserves its energy, slowly digesting leaves that are tough and full of oil.
To help break down their food, the digestive tract of the Koala is adapted with a long, thin tube branching from their intestines. This may be up to two metres long. It’s believed that this tube probably helps break down the poisons in gum leaves – but its exact purpose remains a mystery.
Barrenjoey Peninsula – many gum trees, but few are Koala favorites
The Barrenjoey Peninsula has an abundance of different kinds of eucalypt trees, and Koalas have been known to feed on just about all of them.
The Spotted Gum is by far our most common gum tree on the Peninsula - but it’s not the favorite of the Koala. Instead, they strongly prefer the Grey Gum (Eucalyptus punctata). Of the 38 trees known to be favoured Koala food trees, 31 are Grey Gums.
While the Grey Gum makes up only 5% of the trees on the Peninsula, it is 45% of the trees in which Koalas were reported. The preference of the Koalas for this species has long been recognised locally and it is known to be a staple food tree from nutritional studies.
In addition to the Grey Gum, our Barrenjoey Koalas have favoured:
- Scribbly Gum
- Swamp Mahogany
And to a minor extent, also:
- Narrow-leaved Black Peppermint (an introduced species)
When they need shelter, Koalas aren’t so selective. They will use a variety of trees for shelter during the day or during harsh weather. These include:
- Brush box
- Acacia trees
What is its life cycle?
In general, Koalas are solitary animals. However, they have a complex social hierarchy: one dominant male will have a territory that includes a number of females. On the edges of this territory, younger males try to gain a foothold – usually by attempting to mate with available females. While they may be sexually mature, these young males are often prevented from mating, as they are driven off by older males.
In breeding season, male Koalas are highly vocal. They advertise their mating prowess with loud, snarling coughs and bellows. Their mating songs ring through the trees between September and January, and they are answered by high-pitched, tremulous calls of the female Koalas.
A female Koala can breed from about two years of age. She gives birth to a single, tiny newborn Koala after a gestation of about 35 days. The newborn is blind, hairless and so tiny it could fit on your thumbnail! It drags itself into its mother pouch and attaches to one of her two teats. Like the wombat, the Koala has a pouch that opens towards the rear. However, the Koala pouch is ringed with strong muscles to stop their young from falling out. Deep in its mother’s pouch, the baby Koala suckles for several months, growing bigger and stronger. By about seven months it is too large for the pouch. Instead it rides on her back, or nestles into her chest while she sleeps.
The young Koala will be eating an exclusive diet of gum leaves by the time it is one year old. By this time, its mother is ready to mate again. When it reaches the age of two, the juvenile Koala becomes independent. They leave to find their own home range, and they may have to journey some distance if they cannot find any territory close to home. But sadly, this can prove fatal: forced to cross open spaces, the Koala may be hit by a car or be attacked by roaming domestic dogs.
What are the threats?
Until the early 1950’s, the major threats to Koalas in Pittwater were known to be bush fires (especially intense fires that scorch or kill the tree canopy), motor vehicles and dogs.
However, the 1950s and 1960s saw the emergence of concern about a new threat: the loss of trees due to extensive housing development in the Newport-Avalon-Palm Beach area. This has remained the chief threat ever since.
In addition to the ongoing threat of habitat destruction, Koalas have also suffered from more direct threats. The leading causes of Koala deaths in New South Wales are:
- Motor vehicles
- Attacks by dogs and other carnivores. Koalas on Barrenjoey Peninsula have been particularly susceptible to dog attacks. Between 1947 and 1989, 24% of Koala deaths were caused by dogs
- Chlamydial diseases - Koalas are particularly susceptible to disease compared to other marsupials. The suite of diseases associated with the bacterium Chlamydia psittaci are the most common diseases found in Koalas. (Reports of chlamydial diseases in the Barrenjoey Peninsula Koalas have been relatively low, but it still represents a major threat for such a small colony.)
What can we do to protect our native wildlife?
There are many things we can do to protect our remaining wildlife. These include:
- Conserving remaining bushland
- Identifying road-kill blackspots and erect warning signs, reduce speed limits or provide safe crossing points to reduce wildlife fatalities
- Controlling domestic cats and dogs, and control foxes
- Preserving trees in urban areas
- Enhancing possible habitat by planting suitable food trees
- Creating wildlife corridors (between reserves on Barrenjoey Peninsula, and between Barrenjoey Peninsula and Ku-ring-gai Chase National Park)
- Stopping the degradation of habitat (such as the dieback of eucalypts and the spread of non-eucalypt vegetation)
- Improved fire management – fires are known to cause wildlife deaths and they can also reduce food resources, especially just after bush fires when there is no fresh foliage on burnt trees
- Rehabilitating sick, injured or orphaned wildlife
- Educating the community about our remaining wildlife
- Learning more about our native wildlife at one of our many free Council events
Updated: 28 Sep 2015