Koala Survivor against the odds

BY MARK KELLETT

Cuddly, placid and vulnerable, the koala is loved both in Australia and overseas, and has become one of Australia’s mascots. Surely, only in Australia’s sheltered isolation could such a helpless creature have persisted. But the koala’s history shows it to have been a wonderfully specialised animal, surviving despite formidable challenges.

T

HE EARLIEST known koala fossils are of four extinct species from 25 million years ago. Palaeontologist Professor Michael Archer has suggested that even then they may have lived in and on eucalypts, which were at that time a rare type of tree. In so doing they moulded their entire biology around the limitations of their meagre food (see ‘Living on Eucalyptus’ box on page 74). As rainforest gave way to bushland, the number of koala species declined to one, but this lucky survivor became abundant along with the eucalypts. Though they thrived in the prehistoric bush, koalas were far from

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safe. They would have been potential prey for the arboreal marsupial carnivore Thylacoleo carnifex and for thylacines. Then, as now, their young were sometimes taken by powerful owls and wedge-tailed eagles. More destructive to koalas, though less prevalent, would have been environmental disasters. Koalas die of starvation and thirst as eucalypts shed their leaves in serious droughts, while crown fires, which burn through the forest canopy, either roast koalas outright or leave them to starve in the ashy aftermath. The arrival of the first Aboriginal people between 60,000 and 45,000 years ago changed the factors that checked koala populations. The

Aboriginal practice of ‘fire-stick farming’ would be a boon to koalas. By establishing a regime of frequent, low intensity fires, Aboriginal people encouraged useful plants and animals. Since these managed fires rarely spread into the canopy, koalas seem generally to have benefited from the practice. However, the koala’s predators also changed. Observations by European explorers and missionaries suggest that some Aboriginal tribes refused to hunt the marsupial, while others did so PICTURE ABOVE: Koala and young, by John William Lewin, 1803. Courtesy of the State Library of New South Wales, ML 896.

enthusiastically, and still others hunted it for food but did not use the pelt. The ancient marsupial predators became extinct, to be replaced by the more intelligent and agile dingo. The combined effect of these Aboriginal practices seems to have kept the koala rather uncommon in bushland in what are now Victoria, New South Wales, Queensland and South Australia. Certainly, it was not until 1798 that the animal was first noticed by a group of convicts sent on an official expedition from Sydney to disprove the rumour that it was possible to walk to China. John Price, a literate servant of Governor John Hunter who was sent to keep a journal of the expedition, observed “There is another animal which the natives call a cullawine, which much resembles the sloths in America.” Four years later, during his unsuccessful attempt to cross the Blue Mountains in 1802, Ensign Francis Barrallier of the NSW Corps came across a group of Aboriginal people butchering a koala. He was able to obtain its paws, which he sent to Governor Philip Gidley King preserved in brandy. A year later he captured three living animals, which were described in the Sydney Gazette and New South Wales Advertiser: An animal whose species was never before found in the Colony is in His Excellency’s possession. When taken, it had two Pups, one of which died a few days since. This creature is somewhat larger than the Waumbat and although it might at first appearance be thought much to resemble it, it nevertheless differs from that animal. The fore and hind limbs are of equal length, having sharp talons at each extremity, with which it must have climbed the highest trees with much facility. The fur that covers it is soft and fine and of a mixed grey colour; the ears are open; the graveness of the visage, which differs little in colour from the back, would seem to indicate more than ordinary portion of animal sagacity; and the teeth resemble those of a rabbit. The surviving Pup generally clings to the back of the mother, or is caressed by her with a serenity that appears particularly characteristic; it has a false belly like the apposim, its food consists solely of gum leaves, in the choice of which it is excessively nice.

The animal was not given a scientific name until 1816, when a French anatomist, Henri de

Blainville, gave it the genus name Phascolarctos (pouched-bear). A year later it was given the species name cinereus (ashy-grey) by Georg Goldfuss, a German naturalist. Although there was some confusion in the next decade or so as to the animal’s scientific name, eventually Phascolarctos cinereus was accepted. By this time the animal was being popularly, if rather inaccurately, described as the native sloth or monkey, but more commonly as the native bear or koala (originally koolah) bear. After the arrival of Europeans, the Aboriginal people and the dingos were displaced. Though domestic dogs and some convicts doubtless hunted koalas, they do not seem to have done so with the same intensity as their predecessors.

The disappearance of the Aboriginal people, however, also led to a return of devastating crown fires. In 1792, David Collins described the lands around the Sydney colony as being “everywhere on fire”. Similar fires were reported in 1797. Doubtless hundreds of koalas were killed in these infernos, as they have been in many bushfires since, particularly the fires of Black Thursday in 1851, Black Friday in 1939, Ash Wednesday in 1983 and the severe fires of 2006. The net effect of the arrival of Europeans, at least to begin with, seems to have been an increase in koala numbers. By 1836, the previously rare koala was described by the surveyor William Govatt as “...numerous on the ranges leading to the Cox’s River, below the mountain precipes, and also on the ravines

Illustration from Perry's Arcana, a rare book published in 1810. The author seemed unimpressed by the koala, writing: “...we are at a loss to imagine for what particular scale of usefullness or happiness such an animal could by the great Author of Nature possibly be destined...” Image from the collection of National Archives of Australia, A1200:L20127.

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Under most circumstances nearly all joeys can expect to live to adulthood. This combination of modest birth rate and low infant mortality gives koalas a reasonably high reproductive capacity.

which open into the Hawkesbury River, as well as in various other parts of the colony...”. Similar population increases followed the displacement of Aboriginal societies in other parts of New South Wales and Victoria. Clearing of forest by the early European settlers, while often very wasteful, was limited in scope. However, when diggers turned their

hands to farming after the gold-rushes of the 1850s and ’60s, land clearing began in earnest. One hundred and fifty years later, at the close of the 20th century, Victoria had lost twothirds of its native vegetation, while the other states in which koalas were found had lost about a third. A koala or two could survive for a while on the scattered trees left in paddocks or on road-side strips, but these

remnants were unlikely to support permanent populations. More viable koala populations survived in uncleared areas that were economically unproductive or deliberately conserved, and these islands of bush in the sea of farmland have become the last bastion of many southern koalas. Though Europeans occasionally hunted koalas for food, it was not until the 1870s that they exploited them for the fur-trade. Koalas did not have the best pelt amongst Australian animals, but it was durable and easy to obtain. Initially the skins were sold to Europe, later they were also sold to America and Japan. At the height of the fur trade in the late 1880s, between 10,000 and 30,000 koala skins were shipped each year to London alone. One of the most destructive effects of European settlement on the koala went largely unrecognised at the time. Microbiologists now believe that in the late 19th century the bacteria Chlamydia pecorum was transmitted to koalas, probably from cattle or pigs. Chlamydia infection of the eyes may explain observations by the zoologist Ellis Troughton in Furred Animals of Australia of “...epidemics of some form of ophthalmic disease and periostitis of the skull, introduced as a result of

Koala hunting. View of a truck load of 3600 koala skins which were obtained by a party of hunters in the Clermont area in thirty days. Photo courtesy of John Oxley Library, State Library of Queensland, Image Number: 18937.

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settlement, which is said to have swept away millions of koalas in the years 1887–9 and 1900–3”. Chlamydia infection of the female reproductive tract may also explain the “cystic ovaries” described by Ambrose Pratt in The Call of the Koala and the common perception among zoologists and zoo-keepers of the time that the koala was a “poor breeder”. Though koalas could and did survive, infected females suffered from permanent reduction in fertility, robbing the species of its means of recovering from disturbance. In addition, a population that had weathered an outbreak was prone to endure it again when stressed. By the end of the 19th century, fire, deforestation, hunting and disease had all played a role in greatly reducing the koala population. In New South Wales and Victoria, koalas were confined to isolated pockets of forest. In South Australia they had apparently been exterminated altogether. Only in Queensland did they survive at anything like their numbers before European settlement. As Europeans began to view themselves as Australian rather than British-in-exile, they looked for mascots to represent their nationality. The cuddly and lovable koala was ideal. Attention was drawn to the marsupial’s plight, and there were calls for the species to be protected. Legal protection was extended in Victoria in 1898, New South Wales in 1903, Queensland in 1908 and South Australia, rather too late, in 1912. In Queensland this protection proved rather porous, with ‘open seasons’ in 1915, 1917, 1919 and 1927. Only the outcry from scientists, writers, local businesses, and even the Archbishop of Brisbane as well as a great many ordinary people in response to the killing of more than 600,000 koalas in 1927 brought about the end of the open seasons. Some were not satisfied with this passive protection. In an attempt to ensure the species’ survival, koalas were also introduced to offshore islands which often had never supported them. Koalas were taken to Philip Island by farmers during the 1870s; in 1898 an amateur naturalist, Jim Peters, introduced them to French Island, and in the mid-1920s koalas were taken from there to Kangaroo

ABOVE: A mother northern koala with its offspring. She will care for her joey for a year, though it will stay close to her for another 6–12 months afterwards. BELOW: A southern koala enjoys a siesta. Southern koalas have darker and denser fur than those from the northern parts of the species’ range.

Island. These island populations have served their purpose and, for example, have led to the reintroduction of koalas to South Australia from Kangaroo Island. However, conservation headaches are developing on some islands as koala populations threaten to eat themselves out of house and home. The threats facing the koala today are complex, varying from place to place and from population to population. The ancient arm-in-arm menaces of drought and fire still do great damage, even locally exterminating koala populations. In rural areas, logging and clearing for farm use, though now largely controlled by law, can still reduce koala habitats or, worse, confine them to small, isolated pockets of bush. Such ‘island’ populations, surrounded by farmland and left to grow unchecked, are threatened with starvation as they over-browse and kill their trees. In areas where koala habitat has been overtaken by the suburbs, they now exist only in parks and roadside stands of trees and are being hit by cars and mauled by dogs. In most mainland areas, these types of stresses have caused outbreaks of Chlamydia that increase casualties and reduce capacity for population recovery. The history of the koala has been one of survival against the odds. Slowmoving and slow-witted, this marsupial would seem very vulnerable to a wide range of threats. Though their reproductive capacity has in the past allowed them to make good their losses rapidly, koalas now have problems that act to neutralise that advantage. It is clear that there is no simple formula for protecting the koala. As vertebrate ecologist, Dr Murray Logan of Monash University says, the problems facing each population must be examined and dealt with individually if the species is to survive.

The Author Dr Mark Kellett is a biologist and freelance writer.

Further Reading The Koala: Natural history, conservation and management (second edition) by Roger Martin and Kathrine Handasyde, University of New South Wales Press, 1999. Furred Animals of Australia by Ellis Troughton, Angus and Robinson, 1946. ◆ 74 Australian Heritage

LIVING ON EUCALYPTUS

Koalas have specialised on a particularly difficult diet. Though eucalyptus leaves contain enough water to meet the animal’s needs, they are not very nutritious. To survive, koalas have evolved one of the longest digestive tracts for an animal of its size, to enable microbes to break down the leaves into a form that can be absorbed. Recent research by Dr Murray Logan of Monash University has shown that koalas also ‘chew the cud’ like a cow, chewing semidigested food a second time to make the microbes’ job easier. Even so, it can take eight days or more for a koala to complete digesting its food. To make matters worse, eucalyptus leaves contain toxic turpenes and phenolics. Though able to detoxify them, koalas select leaves that have the lowest possible amounts of these chemicals. Even with all this digestive machinery, koalas get very little energy from their food. As a result, they have economised almost all other aspects of life to the bare minimum. Nowhere is this more obvious than with their brain, which is only about a third of the size of brains in similar-sized marsupials. It seems that the energetic requirement of a large brain is beyond the energy output that can be generated from a diet of eucalyptus leaves. As a result,

koalas have a fairly limited learning capacity. This lack of intellect does not seem to impede the koala in the least, as its behaviour is also simplified to conserve energy. It sleeps more than twenty hours a day, only stirring in the evening to browse. Generally koalas sleep and feed in the same tree, though in bad weather they may seek shelter elsewhere. They are remarkably solitary animals, their social interactions confined to competition between males, mating and caring for their young. The koala’s reproductive capacity has certainly not undergone economies. Females mature at about two years old, and a healthy female can breed once a year for about ten years, normally giving birth to a single joey each year. Under most circumstances nearly all these joeys can expect to live to adulthood. This combination of modest birth rate and low infant mortality gives koalas a reasonably high reproductive capacity. This was demonstrated by the growth of the captive population at the Koala Park in Queensland which increased from four to sixty-five in just six years. It is this high fertility that has enabled the koala to make good the losses that it has suffered throughout its history.