Koalas (Phascolarctidae)

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Koalas

(Phascolarctidae)

Class Mammalia

Order Diprotodontia

Family Phascolarctidae


Thumbnail description
A medium-sized stocky herbivorous marsupial with a bear-like appearance, characterized by a broad face and bulbous nose, large, rounded fluffy ears, relatively long legs with large paws and powerful claws, and a short tail

Size
28–31 in (72–78 cm); 11–26 lb (5.0–11.8 kg)

Number of genera, species
1 genus; 1 species

Habitat
Subtropical/tropical dry eucalypt forest and woodland

Conservation status
Lower Risk/Near Threatened

Distribution
Eastern Australia

Evolution and systematics

The koala family, Phascolarctidae, are believed to have diverged from their nearest marsupial relatives, the wombats, around 24 million years ago (mya). At least six different members of the koala family evolved. The earliest fossil record of a koala was a browser, Perikoala palankarinnica, some 15 mya. More recently, a giant koala, Phascolarctos stirtoni, was a third as large again as our present day koala, but is believed to have died out along with other marsupial megafauna some 40,000 years ago, at around the time that aboriginal hunter-gatherers colonized Australia. Only one species, Phascolarctos cinereus, survives today. Phascolarctos is from the Greek words for "leather pouch" and "bear," while cinereus means "ash-colored."

There are three subspecies of koala, Phascolarctos c. victor, native to the state of Victoria; Phascolarctos c. cinereus, native to New South Wales; and Phascolarctos c. adustus, native to Queensland. Koalas in the north have shorter coats and are smaller than their southern cousins, and genetic studies have confirmed significant differences between the two populations, as well as suggesting that there may be a number of distinct subpopulations in the north. Southern populations appear more homogenous, probably as a result of the numerous translocation projects which have taken place.

The taxonomy for the koala is Phascolarctos cinereus (Gold-fuss, 1817), New South Wales, Australia.

Physical characteristics

The comical, appealing, "teddy bear" appearance of the koala has made it Australia's iconic animal. Despite the misleading popular name "koala bear," koalas are not, of course, related to the omnivorous bear family, but are herbivorous marsupials. They are medium sized, with a head and body length that can be as short as 24 in (60 cm), or as long as 33 in (85 cm), but is usually in the range 28–31 in (72–78 cm). Body weight can also vary considerably, from as little as 8.8 lb (4 kg) for a northern female, to as much as 33 lb (15 kg) for a southern male, but the usual range is 11–26 lb (5.0–11.8 kg). Males are up to 50% larger than females, and there is a significant size difference between koalas in Queensland,

where males average 14.3 lb (6.5 kg) and those further south, where males average 26 lb (11.8 kg).

The koala has a compact body with a broad head, large nose, and small eyes. The ears are large and rounded with white edges. Koalas have only a vestigial tail, which is of no assistance in climbing, but they have long, strong limbs, with large paws and sharp claws which are well adapted to grip smooth-barked eucalyts. Fore and hind feet have five digits, all with sharp, recurved claws, except for the first digit of the hind foot, which is short and broad. The first and second digits of the forefeet are opposable to the other three, allowing the animal to grip smaller branches and climb into the outer canopy in search of fresh leaves. The second and third toes of the hind feet are fused, with a double claw.

Koalas do not use dens nor shelters, so their fur is important for insulation. Southern koalas have dense, woolly coats, with thicker, longer fur on the back than the belly. Koalas living further north in warmer subtropical and tropical regions have shorter coats (also lighter in color), sometimes appearing almost naked. The color and pattern of coats varies considerably between individuals and with age, from gray to tawny, with white on the chin, chest, and forelimbs and whitish dappling on the rump. Males have a large chest gland that is used for scent marking trees. Females have a marsupial pouch opening to the rear and containing two teats.

Distribution

Australia's koala population is found in a broad coastal swathe down the eastern seaboard, from the Atherton tablelands in north Queensland to southwestern Victoria. Although this is an area of several hundred thousand square miles (kilometers), deforestation, habitat degradation, and historic persecution mean individual populations within this range are fragmented and often isolated.

Historically, the geographical range of koala populations was broadly similar to today, but extended into South Australia and southern parts of Western Australia. Land clearance and hunting caused populations within this range to contract, and in many cases become extinct. However, intensive koala management and reintroduction programs have reversed this decline in many places, particularly in the south, and koalas are now locally common where suitable habitat survives. A number of localized populations have been re-established in South Australia and Western Australia.

Habitat

Koalas feed almost exclusively on eucalyptus leaves, so their habitat is invariably eucalypt forest and woodland. However, they can tolerate a surprisingly diverse range of environmental

and climatic conditions. In the tropical north habitat is often dense thicket, with high year-round temperatures and strong seasonal rainfall. Rainfall is also high in the temperate mountain rainforests of the south, but winters can be much colder. This fertile habitat can support populations as high as three animals per acre (0.4 ha), a stark contrast to the semi-arid open woodland habitat of the west, where a single animal may require 250 acres (100 hectares) to survive.

In temperatures above 77°F (25°C) koalas use evaporative cooling in their airways to regulate temperature, by breathing rapidly, but reduce water loss by decreasing the amount of water in their urine. In cold temperatures koalas, like humans, conserve heat by reducing blood flow to extremities, and have also been seen to shiver, a means of producing heat by rapid muscle contraction.

Behavior

Koalas are essentially solitary animals, with very little social interaction other than during the breeding season. Adults occupy fixed home ranges. Range size depends on the productivity of the environment, but can be as little as 2.5 acres (1 ha) for a male in a fertile habitat, and half that for a female. Within this range an animal may live much of its life in only a dozen favored trees. A dominant adult male's range will overlap the range of up to nine females and a number of subordinate and subadult males.

Within the area of a stable social group individual koalas will "own" a number of food trees and "home range trees" marking the edge of their range. A koala trespassing into an "owned" tree may be aggressively attacked by the resident, but scent markings and scratchings usually warn animals that a tree is under possession. Other trees where ranges overlap will be shared, and it is here that limited social interaction takes place.

Koalas are largely nocturnal, feeding and moving after dusk. They rarely leave the security of the trees, descending to the ground only to move to another food tree, or to consume soil, which aids digestion. Koalas walk on four legs, run with a bounding gait, and can swim if necessary.

As one adaptation to their low-energy eucalyptus leaf diet, koalas sleep up to 20 hours a day, usually wedged comfortably into the fork of a tree. Even when awake, koalas spend much time resting, and feeding occupies only 10% of their day.

Activity livens up in the summer breeding season, when dominant males will attempt to defend their territory for breeding rights with resident females. At this time of year males use their chest gland to scentmark tree trunks and can often be heard bellowing, apparently to warn off rival males and attract females. This deep, grunting bellow often provokes responses from other males in the area. At night males move around more, fighting with any competing adult males that they encounter, or mating with estrous females.

Koalas have a range of other sounds for communication. Mothers and babies make soft clicking, squeaking sounds, and

gentle murmuring, or will grunt if annoyed. All koalas are capable of a distressing, high-pitched cry like a screaming baby when afraid.

Feeding ecology and diet

Australia has some 650 species of eucalypt, but koalas are choosy eaters, and feed on only around 30 species, with just a handful, including river red gum, gray gum and manna gum, preferred. They have occasionally been known to eat noneucalypt leaves, including acacia, mistletoe and box. Koalas eat about 1.3 to 1.8 lb (600 to 800 g) of leaves a day.

Koalas reach their food by climbing high up smooth, vertical eucalypt trunks, gripping with their sharp foreclaws and using their powerful front legs to pull themselves up, while bringing their hind legs up to their front. Although they generally move slowly and laboriously to conserve energy, they are capable of surprising agility and can leap 6 ft (2 m) from trunk to trunk.

Eucalyptus leaves are low in nutrients, contain a large proportion of indigestible cellulose and lignin, and are full of toxic chemicals. Koalas have evolved a number of ways to cope with this poor diet. They avoid the most toxic species, and vary their choice of food tree throughout the year as toxin levels vary seasonally in some species. The koala's liver is capable of detoxifying and excreting some poisonous compounds from those species they do eat. Koalas have large cheek pouches, to handle large amounts of poor quality forage, and well-developed teeth, which include a single premolar and four molars in each jaw, which grind the fibrous leaves to a fine paste. This is then digested by microbial fermentation in the animal's unusually long cecum (a blind sac in the digestive tract, between the junction of the small and large intestines). A koala's cecum can be more than 75 in (2m) long.

The low energy yield of the koala's diet explains their slow, sedentary lifestyle. However, it is a myth that koalas are drugged by the poisonous compounds in eucalyptus leaves. What is true is that koala have one of the smallest brains of all marsupials relative to body size—only 0.2% of body weight—and this has been explained as a further response to diet, since the brain is one of the most energy-consuming of the body's organs.

Koalas obtain most of their water from leaves, but occasionally drink at streams, and in captivity often choose to drink fresh water.

Reproductive biology

Koalas are polygynous. During the summer breeding season a dominant male will attempt to mate with any estrous females he encounters in his range. Copulation lasts only a

couple of minutes, with the male mounting the female from behind and holding her against a branch. Females are sexually mature at two years old, but generally do not start to breed until they are older—full physical maturity is reached at about four years old in females, five years old in males.

Females have an estrous cycle of about 30 days, and usually breed once every year, between November and March. Gestation lasts about 35 days before a single young (very rarely twins) is born, weighing less than 0.02 oz (0.5g) and measuring about 2 cm long.

The tiny newborn koala crawls into the mother's large pouch and attaches itself to one of the two teats. By 13 weeks the young joey will have grown to about 2 oz (50 g), and by 22 weeks its eyes open and it begins to poke its head out of the pouch for the first time. Joeys have a pouch life of five to seven months, after which they spend most of their time out of the pouch, clinging to the mother's belly and later sitting on their back. Joeys are weaned at six to 12 months, but towards the end of their pouch life also feed regularly on soft, partially-digested leaf material passed through the mother's digestive tract. This "pap," which contains a high concentration of microorganisms, is believed to be important in introducing

to the young koala's gut the microbes it will need to digest eucalyptus leaves.

A joey will remain with its mother until about one year old, when it weighs around 4.4 lb (2 kg) and can begin to fend for itself. Juveniles disperse to find their own home range at about two years old, searching for another breeding group to join, but becoming nomadic if no area is available.

Koalas can live in excess of 10 years in the wild, and 17 years or more in captivity. Longevity is probably related to stress factors such as habitat pressure, disease, and human interference.

Conservation status

Koala conservation is a complex issue. Populations are under severe pressure from habitat loss in many parts of Australia, yet in some areas the koala is common or even over populous.

Before 1900 koalas numbered in the millions, despite regularly suffering enormous losses to bushfires and disease epidemics. But in the first decades of the twentieth century extensive forest clearance and large scale hunting for the koala's warm, cheap, durable fur saw populations crash. The slaughter reached a peak in 1924, when over two million koala pelts were exported to Europe and America, and by the end of that year the species had been exterminated in South Australia and nearly wiped out in Victoria and New South Wales. A healthy population surviving in Queensland was next to suffer when in 1927 the state government bowed to commercial pressure and allowed an open season—600,000 more skins were exported.

Public outcry in Australia and abroad eventually resulted in legal protection, and since the 1920s intensive conservation measures, including captive breeding and translocation efforts, have allowed populations to partially recover. Today koalas are still under intense pressure in many parts of their range, but are not classified as threatened. The Australian government lists koalas as vulnerable, but has not put them on the country's endangered list. The World Conservation Union (IUCN) classifies koalas as Lower risk/Near Threatened, and lists habitat loss and degradation due to timber

felling and urbanization, and human disturbance, particularly through fire, as the major threats.

Unfortunately, koalas inhabit precisely those eastern seaboard regions of Australia that are seeing most rapid urbanization and agricultural development. In the past 200 years an estimated one-third of Australia's eucalyptus forest has disappeared, and in semi-arid parts of Queensland, thousands of acres of woodland are still being cleared for agricultural use every year. Urbanization and tourist development along the coastal strip is further fragmenting eucalyptus woodlands. Bush fires caused by negligence or arson account for thousands of deaths each year, while an estimated 10,000 koalas are killed in road accidents. Koalas put up no resistance to attacks from domestic dogs, and do not cope well with stress, having abnormally small adrenal glands. There is also evidence that inbreeding in isolated, fragmentary populations is leading to physical abnormalities.

Despite all these pressures, there are actually locations where koala populations have thrived to such an extent that they are causing environmental damage. Koalas were translocated to a number of islands where they were not found naturally as long ago as the 1870s. Populations on Phillip and French Islands in Victoria, and Kangaroo Island in South Australia have grown so large that the unpalatable prospect of culling has been proposed. Thousands of animals have been relocated back to the mainland, causing similar overcrowding problems in some locations, and contraception is being investigated as a more publicly acceptable alternative to culling.

One possible explanation for these overpopulation problems is that the island populations are free of chlamydia, a disease that is now thought to have been endemic in koalas for many years, and may have acted as a natural population control, remaining benign when conditions were good, but killing off weaker animals during stressful times such as when habitat is reduced.

Some koala conservation work, including purchase of land for protected reserves, is being carried out by state authorities, but much koala conservation and research is in the hands of charities and privately-run welfare organizations. The koala's cute and cuddly appeal helps raise funding for such non-government organizations.

One problem in planning conservation management is the difficulty in obtaining accurate population figures. The Australian Koala Foundation suggests numbers have dropped from 400,000 in the mid-1980s to between 40,000 and 80,000 today, but this estimate can only be an educated guess. The Foundation is compiling a national atlas of surviving koala habitats, which will provide a tool to lobby for habitat conservation.

Significance to humans

The name koala is believed to have originated from Aboriginal dialect names for the animal, which include cullewine, koolewong, colo, colah, and koolah. One suggested translation for these Aboriginal names is "no water," referring to the koala's ability to largely subsist on moisture from leaves.

Australia's Aboriginal people have long hunted koalas for food—they make a slow-moving target easy to hit with a boomerang. But traditional Dreamtime stories teach Aborigines that if they fail to respect the animal they will be visited by a terrible drought. Tradition dictates that while koalas may be eaten, they must not be skinned nor their bones broken.

No such respect was accorded by early European settlers who shot koalas for "sport" and later for fur. Today koalas have a different, but equally important commercial significance, as animal ambassadors for the tourist trade. So important is the koala as a tourist draw card, particularly to the important Japanese market, that moves by state governments to ban "koala cuddling" on the grounds that it is stressful for the animals, were opposed (unsuccessfully) by tourist authorities.

Where populations are healthy wild koalas are easy to observe, but most tourists see koalas in zoos and animal sanctuaries, where petting, if not cuddling, is allowed. The Australian federal government strictly controls exports of live koalas, and this, combined with the problems of satisfying the koala's very specific dietary requirements, mean there are only a handful of zoos outside Australia, in the United States, Japan, Germany, and Taiwan, where koalas are exhibited.


Resources

Books

Australian Koala Foundation. Proceedings of a Conference on the Status of the Koala in 2000, Incorporating the Ninth National Carers Conference—Noosa, QLD. Brisbane: Australian Koala Foundation, 2000.

Lyons, K., A. Melzer, F. Carrick, and D. Lamb, eds. The Research and Management of Non-urban Koala Populations. Rockhampton: Koala Research Centre of Central Queensland, 2001.

Martin, R. W., and K. A. Handasyde. The Koala: Natural History, Conservation and Management. Sydney: University of New South Wales Press, 1999.

Saunders, N. R., and L. Hinds, eds. Marsupial Biology: Recent Research, New Perspectives. Sydney: University of New South Wales Press, 1997.

Strahan, R., ed. The Mammals of Australia Sydney: New Holland Publishers, 1998.

Periodicals

Clark, T., N. Mazur, S. Cork, S. Dovers, and R. Harding. "Koala Conservation Policy Process: Appraisal and Recommendations." Conservation Biology 14, no. 3 (2000): 681–690.

Ellis, W. A, P. T. Hale, and F. Carrick. "Breeding Dynamics of Koalas in Open Woodlands." Wildlife Research 29 (2002): 19–25.

Martin, R. W. "Managing Overabundance in Koala Populations in South-eastern Australia: Future Options." Australian Biologist 10, no. 1 (1997): 57–63.

Moore, B. D., and W. J. Foley. "A Review of Feeding and Diet Selection in Koalas (Phascolarctos cinereus)" Australian Journal of Zoology 48 (2000): 317–333.

Organizations

Australian Koala Foundation. Level 1, 40 Charlotte Street, Brisbane, Queensland 4001 Australia. Phone: (7) 3229 7233. Fax: (7) 3221 0337. E-mail: [email protected] the koala.com Web site: <http://www.savethekoala.com>

Stephen and

Ann Toon