Threats to the koala

Survival MD

Survival MD Ebook

Get Instant Access

Between 1788 and 1921, 35.3 million hectares [of forest] were ring-barked and partially cleared, which corresponds with 44% of the land area of New South Wales.1

The fur trade was not the only threat the koala had to face during the late 1800s and early 1900s.2 Australia's native animals have always had to contend with natural disasters such as fire and drought, but other dangers are a direct result of human settlement. Habitat loss and fragmentation, disease, overpopulation, inbreeding, dog attacks and road accidents all have taken their toll on the koala. In this chapter we explore the impact of these threats, in the hope of gaining an insight into how this might be minimised in the future.

The biggest danger facing the koala is loss of habitat and habitat fragmentation as a result of clearing. 'Fragmentation' is when a large area of habitat is cut into a number of smaller pieces, which then become isolated from each other by agricultural clearing, roads and the establishment of residential areas. The fragments of koala habitat that remain often contain only a few animals, not enough to sustain a population. Any increase in local mortality rates, whether due to drought, dog attacks, diseases or road accidents can lead to local extinction. One example of an impending localised extinction is in Avalon and Palm Beach, on Sydney's northern beaches. In 1970, there was a local population of over 120 animals, but by 1989 urban growth had reduced that number to eight.3 Sadly, even if any of these animals are left they are likely to be too old now to breed.4

The extent and speed of habitat loss in Australia is frightening. Since European settlement, localised clearance of eucalypts ranges between 33 and 92 per cent, while Acacia habitats, that are known to support low-density koala populations, have decreased by over 80 per cent.5 In New South Wales alone, by 1890 the area of land that had been leased or alienated through land grants and sales was estimated to be 98.5 per cent, though this appears to be an overestimate.6 Between 1893 and 1921, 25.7 million hectares of forest or 32 per cent of the state's overall area were ringbarked and partially cleared.7 This represents an area greater than England, Scotland and Wales, which together have an area of 23 million hectares. As Australia's population grew, national land clearing between 1945 and 1995 resulted in as much vegetation being cleared as in the previous 150 years.8

In recent years, vegetation clearing has continued, particularly in New South Wales and in Queensland.9 Between 1983 and 1993 the estimated annual average clearing rate of native vegetation was 150 000 hectares in New South Wales and 300 000 hectares in Queensland. Over the same period, Victoria's average clearing rate was 7780 hectares, South Australia's 9300 hectares. Most of the land cleared in South Australia, and some in Victoria, was native grasslands and mallee forests, neither of which are koala habitats.10 Only 14 per cent (1385 hectares) of the vegetation cleared in South Australia between 1983 and 1995 could be considered koala habitat and in addition to clearing as little koala habitat as possible both South Australia and Victoria have concentrated on rehabilitating forest remnants and managing koala habitat that has been overbrowsed.11

The Queensland Environmental Protection Agency has estimated that between 1991 and 1995, 285 000 hectares of land were cleared per year. This increased to 320 000 hectares per year in 1996 and 1997 and an incredible 425 000 hectares per year between 1997 and 1999. The extent of the clearance is perhaps easier to visualise if you consider that this is equivalent to ten average suburban blocks being cleared every minute!12 This compares with figures from 2001 that suggest 100 000 hectares were cleared per year in New South Wales, 17 000 hectares in Tasmania, 12 700 hectares in the Northern Territory, 6000 hectares in Western Australia, 2500 hectares in Victoria and 1600 hectares in South Australia. It must be pointed out that these figures reflect not only the amount of native vegetation in each state but also the different state legislations to protect it.

Despite the 1999 introduction of the Land Management Act, clearing in Queensland reached a peak of 758 000 hectares during 1999-2000, falling back to an average of 577 000 hectares for the 1999-2001 review period.13 The average clearing rate for the period from 2001 to 2003 showed a small decrease, to 528 000 hectares per year.14 Nationally, the estimated rate of native vegetation clearing in 2000 was 564 800 hectares, a total which ranked Australia fifth in world land clearing. Only Brazil, Indonesia, the Sudan and Zambia had worse clearing records at that time.15

Mounting public reaction against the broadscale clearing in Queensland prompted the Queensland Labor Government and the federal Liberal Government to announce in May 2003 a plan to end broadscale clearing by 2006, a proposal applauded by environmental groups who congratulated the two governments for working together.16 In order to prevent panic clearing a moratorium was announced but, before it came into effect, applications to clear 740 000 hectares had already been lodged. As a result, the Wilderness Society has estimated that 4500 hectares of native vegetation were still being cleared each week.17 In 2005, however, the Australian Government pulled out of the plan and eventually criticised it strongly. The former federal Minister for Agriculture, Fisheries and Forestry (a Queensland National Party Member and thereby representative of the Queensland farmers) was so incensed that he released a press statement suggesting that 'mindless bans' on land clearing were now being imposed in Queensland and that the new laws were 'draconian'.18

Despite the federal government's opposition, Queensland's Labor Government followed through with the introduction of their 'draconian' laws. All clearing of mature bushland in Queensland ceased on 31 December 2006. Urban areas and significant areas of regrowth can still be cleared, but this historic decision protects around 20 million hectares of bushland that could otherwise be cleared, and is a huge advance in the protection of wildlife habitat that should be applauded.

The estimates of broadscale Eucalyptus clearing may overstate the loss of koala habitat, first, because they include eucalypt communities beyond the koala's natural range and, second, because the koala's distribution is not uniform within its known range.19 Nonetheless, the sheer size of the numbers gives a powerful indication of the extent of the habitat loss suffered by koalas and other Australian forest-dwelling species. One alarming estimate of the annual koala losses as a direct result of land clearing in Queensland puts the death rate of koalas at 19 000. In addition, land clearing in Queensland was calculated to kill—annually—342 000 possums and gliders; over 7500 echidnas; 233 000 kangaroos, wallabies and rat kangaroos; 29 000 bandicoots; 1.25 million small carnivorous marsupials; and 196 000 native rodents.20

A similar, more recent report on the impact of approved land clearing of native vegetation in New South Wales calculates that a staggering 104 million mammals, birds and reptiles have died or will die as a result of the legal clearing of 639 930 hectares of vegetation between 1998 and 2005. As it does not include the impact of illegal clearing, this figure must be

A scene common to many inland towns and settlements in the early 20th century. The trees that grew here were used to build houses and fences; the land for agriculture.

considered an underestimate.21 It can only be hoped that changes to the Native Vegetation Act2003, and the implementation of the Native Vegetation Regulation 2005 in December of that year, will drastically reduce the clearing.

The koala also has to contend with disease. There are numerous anecdotal reports of outbreaks of disease in koala populations, some dating back to the late 1880s. In 1926, Albert Le Souef and Harry Burrell recorded that:

Though at one time extremely numerous, the koala is now, over the greater part of its range, very scarce. This is largely due to a disease which swept it off in millions in the years 1887-8-9, and from 1900 to 1903. This disease took the form of ophthalmia and periostitis of the skull.22

It appears there were many episodes of high mortality, with the then higher population numbers being markedly more prone to fluctuations in size than current koala populations.23 During these outbreaks, dying koalas were found at the base of trees. No longer capable of climbing, they succumbed to starvation, dehydration and infection. In 1919, a disease of the female koala's reproductive tract, later thought to be Chlamydia, was discovered and in the 1920s and 1930s koalas were observed to die from pneumonia and ophthalmic disease.24 After the last open season of 1927, Charles Barrett recorded that disease took a heavy toll on the survivors.25

These early epidemics may have been caused by the bacteria Chlamydia, but debate still rages over its origin, spread and impact. In 1934, Hedley Finlayson documented the disappearance of the koala from some areas in Queensland:

The tenure of the koala in the Dawson Valley seems to have been a waning one for many years, and the last open season reduced it to such an extent that it is now a rare animal in many parts of the valley where it was once formerly very plentiful. The process has been hastened, too, in some places, by an epidemic, and on Coomooboolaroo in the summer of 1929 several were seen in comatose condition at the base of the feeding tree.26

These observations of sick koalas are likely to be the presently known fatal disease known as Chlamydia which is of unknown origin but which has caused significant mortality throughout much of the koala's distribution.

Lunney and Leary offer a detailed account of the koala's decline in Bega, in the south-east of New South Wales. In the mid-19th century the animals were so common that in 1865 it was possible to catch a koala in the main street. From the 1870s through to around 1905 there was a thriving fur trade in the area, but as the region's vegetation was cleared, koala numbers steadily fell. The koala's final decline in Bega is attributed to a combination of habitat loss and a 15-year drought, from 1895

to November 1910, with the spring of 1907 being one of the most drought-affected in memory.27 Disease also appears to have been an important factor, as one record suggests that koalas were still numerous in 1905 and the real decline occurred between 1905 and 1909. During this time koalas were seen 'very sick and dejected in the trees before they were found in their hundreds dead at the foot of trees'. By 1910 the koala had all but disappeared, especially in the open country and it appears that ever since this time koalas have been rare in the Bega region.28

In their study of koala survival in New South Wales, Reed and Lunney include a letter from David Stead of the Wildlife Preservation Society. Dated 6 May 1929, the letter has a postscript from a Mr D.P Evans:

When I was a boy at Bega from 1880 to 1885 almost every tree had its bear, and when I paid visits to the district for several years later I found the bears still very common up to 1892. I returned again in 1895 and found that hardly a bear was to be seen; and now one may ride all day through the paddocks without even seeing one bear where once they were plentiful. I have been told that the sudden (not gradual) disappearance of the bears was due to some disease which killed almost every bear in Gippsland and NSW South Coast.29

Gordon and McGreevy have proposed that despite the numbers slaughtered in 1919 and 1927, koalas were still common in parts of Queensland. After the last open season, koalas were observed to suffer a drastic decline, due to the effects of 'disease'. Koalas were seen sitting, ill and weak, or lying, dead, at the base of trees, in what observers considered an abnormal phenomenon. It is difficult to put a precise date on the outbreak, but anecdotal reports suggest that it spread from one district to another over a period of years during the late 1920s and early 1930s.30

Many diseases are known to impact upon the koala, but the exact nature of the most significant, those which appear to have caused the epidemics mentioned above, remained unknown until the mid-1970s. The Chlamydiae family of bacteria spend most of their lives inside their hosts' cells. Two vets at Armidale's Colin Blumer District Veterinary Laboratory, Frank Cockram and Alan Jackson, were the first to associate the bacteria Chlamydia with keratoconjunctivitis in koalas.31 Cockram and Jackson observed that many wild koalas in northern New South Wales were suffering an acute form of conjunctivitis, also called 'pink eye' because the area of sensitive skin beneath the eyelid, the conjunctiva, becomes inflamed and granular. In acute cases the conjunctiva becomes so swollen that it protrudes out of the eyelid. Cockram and Jackson found Chlamydia bacteria in 29 out of 35 koalas suffering from keratoconjunctivitis and in 1981 they confirmed that it was indeed the causative agent.32 Many animals recover from this disease, but in acute cases it can lead to blindness in one or both eyes.33

The possibility of koala cystitis or 'dirtytail' being caused by the Chlamydia bacteria was proposed in 1978;34 the possible link to koala infertility in 1984.35 In 1984 Brown and Grice confirmed Chlamydia to be the cause of female infertility and other diseases such as rhinitis, cystitis and conjunctivitis.36

Initially, it was thought the diseases associated with Chlamydia were the result of a strain called Chlamydia psittaci, the strain associated with parrots, however subsequent research identified two different species (C. pecorum and C. pneumoniae) of Chlamydia as being responsible.37

Three main syndromes of disease are associated currently with the different species of Chlamydia:

1. Keratoconjuctivitis or 'pink eye' causes a chronic and purulent discharge from both eyes. In severe cases there can be inflammation of the conjuctiva (delicate membranes that line the inside of the eyelids) with keratitis (inflammation of the cornea) and occasionally inflammation of the entire tissues of the eye (panopthalmitis). Koalas affected by this syndrome often fall prey to dogs due to vision impairment.

2. Urogenital Tract Disease generally results in a severe inflammation of the urinary bladder (cystitis), and sometimes can include the urinary tract. This can be seen by a constant urine dribbling and generally results in a red brown stain on the fur of the rump (hence the names 'dirty tail'

or 'wet bottom'). Koalas with this condition often become weak, lose their appetite and may die from malnutrition.

3. Reproductive Tract Disease occurs in females where one or both of the ovarian bursae (that surround the ovary) may distend with inflammatory exudate. Although the ovaries themselves are not cystic, this causes infertility. This syndrome is usually associated with a chronic low-grade cystitis (an inflammation of the urinary bladder).38

Chlamydia-infected koalas. Left: 'pink eye'; and right: 'dirty tail'. (Photos: David Obendorf (left) and S. Brown (right))

Chlamydia is sexually transmitted, however it now appears there may be other means of infection. The bacteria may be transmitted by direct contact, such as that between a mother and her young, or between courting or fighting adults. It is even possible that it can be transferred via tree branches or leaves, via urine or faeces, or potentially via arthropod vectors such as flies, midges and ticks.

Various researchers have considered the role of Chlamydia in the koala's overall population biology. Chlamydia is found throughout most of the koala's distribution and has been proposed as threatening the koala's ultimate survival. Roger Martin and Kathrine Handasyde suggest, however, that as koalas probably have had a long association with Chlamydia the bacteria should be regarded as a normal part of the species' biology and managers should not attempt to establish Chlamydia-free populations. Martin and Handasyde also admit that, based on present knowledge, Chlamydia is the most significant koala pathogen.39

Studies throughout the koala's range reveal that between 70 and 98 per cent of Queensland and Victoria's wild koalas are infected with Chlamydia.40 Despite the bacteria's high occurrence, overt symptoms of disease are comparatively low—9 per cent in south-east Queensland and less than 5 per cent in Victoria. Other studies confirm that a relatively undisturbed koala population can support chlamydial infection without showing overt signs of disease.41 Further support for this hypothesis is provided by the National Koala Survey of 1986-1987, which found the incidence of koalas with overt symptoms of chlamydial infection to be less than 5 per cent.42 Despite the low occurrence of overt disease, the fertility rates for different koala populations appear to be governed by the presence of Chlamydia and vary considerably—from 0 per cent to 84 per cent in infected populations, and from 50 per cent to 83 per cent in uninfected populations.43 The zero fertility rate was the result of the 1963 introduction of infected animals from Wartook Island into a Grampians National Park koala population previously free of Chlamydia.44 The introduction of the infected animals caused most females to become infertile almost immediately and fail to breed the following season. Such a drastic reduction in the fertility rate is unusual, however, and these studies show that the observed fertility rates generally are high enough to sustain population growth.

It is important to highlight that while Chlamydia infection can cause the three disease syndromes described above, the overt expression of disease is not inevitable. It is possible that it is triggered by high stress depressing the koala's immune system, although there is no direct evidence to support this hypothesis.45 Some researchers claim that koalas tolerate chlamydial infection until something such as stress, habitat loss or overpopulation disturbs the host—parasite relationship. Indeed Phillip Reed and his colleagues have argued convincingly that most of the disease outbreaks around the turn of the 20th century followed on from land clearing episodes and were probably exacerbated by adverse climatic conditions such as prolonged drought.46 Ian

Hume proposed that animals living in fragmented habitats are probably nutritionally stressed and therefore more likely to be susceptible to Chlamydia.47 His observations are supported by studies of koala populations with low fertility rates which have been linked to the nutritional stress caused by overbrowsing and high population densities.48

After habitat loss and disease, natural disasters have the biggest impact, of which the most dangerous is fire. Captain James Cook saw fires continually while sailing along the east coast of Australia in 1770.49 The frequent low-intensity fires lit by the Aborigines generally burned along the lower storey of the forest and thus had a limited impact on arboreal mammals such as the koala that live high in the upper tree canopy.50 Falling Aboriginal numbers put an end to a regular burning programme, which allowed the forests' fuel load to accumulate quickly. This resulted in less frequent but more intense fires, a pattern which continues today. Various high-intensity fires are known to have occurred in the 19 th century, including those in south-east Australia in 1851 and 1898.51 The devastating impact of high-intensity fires on koalas is supported by Fred Lewis, who suggested in 1934 that:

Apart from the shooting which so greatly reduced their numbers, I firmly believe that the next most important factor was the bush fires which, during the last twenty or thirty years have ravaged practically the whole of this State [Victoria].

Most birds and animals in the Australian bush can escape, in various ways, from the average bush fire, but the koala falls an easy victim.52

The deliberately-lit Black Friday Fires of 13 January 1939 extended from Victoria to South Australia and must have killed thousands of koalas. More recently, between Boxing Day 1993 and mid-January 1994 the New South Wales Department of Bushfire Services registered some 800 fires. These fires affected 37 of the state's National Parks and nature reserves—more than 90 per cent of the Royal National Park was burned. This high-intensity fire appears to have caused the local extinction of a number of species, although it is not known for certain that koalas were present in the Royal National Park before the fire. If koalas had been present in the Royal National Park it would not be easy for them to recolonise the habitat, because of its relative isolation from other large areas of natural vegetation containing koalas.53

In January 2003 fires of an extraordinary ferocity destroyed over 500 homes in the Australian Capital Territory, and laid waste to an area stretching from southern New South Wales to Wilson's Promontory, in Victoria. Some of these fires were so hot they could be described as 'fire balls'. The heat and the volatility of the natural oils in the eucalypt leaves cause the trees literally to explode into flames. Koalas have no chance of surviving these canopy fires. Unlike other arboreal mammals such as possums, the koala cannot retreat inside a hollow that might offer it some protection because of their large size.

Current fire management practices in vulnerable areas of eastern Australia are based on regular 'hazard reduction' burning via low-intensity fires. This keeps fuel loads to a manageable level, and its importance can be seen in the fact that eucalypt woodlands can register potentially 'severe' fire hazards (that is, fuel loads greater than ten tonnes per hectare) only 2—4 years after low-intensity fires. Despite their efficacy in reducing fuel loads, frequent fires have a significant impact on the forests' species composition by wiping out long-lived woody shrub species that are not fire tolerant. This reduces the area's biodiversity.54

The koala's ability to go for long periods without water is so well-known that drought is not often considered a natural disaster with regard to koalas. It can, however, play an important role within koala populations, especially those that have become isolated within fragmented habitats. In the summer of 1979—80, observers noted a sharp decline in the koala population along Mungalalla Creek in south-eastern Queensland. The region was in the grip of a heatwave and drought, which caused extensive leaf-fall and/or browning of the foliage in food trees along the dry creek. Where the creek and foliage had dried out, the animals were in poor condition, had high tick loads, and it was estimated that some 63 per cent of the local population died. Interestingly, at sites with large, permanent water holes, where the trees were unaffected, the koalas maintained good

Was this article helpful?

0 0
Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

Get My Free Ebook


Post a comment