The Threatening of Australia's Marsupials
By Amber Dilger, 1998
About fifty percent of all mammal species worldwide to have become extinct in the last 200 years have been from Australia, giving Australia the worst record for mammal conservation of any country or continent. Of a total 245 mammalian species, 59 are listed as extinct, threatened, or vulnerable (Short 1994). Most of these extinctions and declines come from two taxonomic groups--the rodents and the marsupials. Because marsupials are so abundant and diverse in Australia, I decided to research the endangerment and conservation efforts regarding marsupial species. Sixty percent of the extinct, endangered, and vulnerable Australian fauna are indeed marsupials; table 1 on the next page lists Australia's threatened marsupial species. Endangered is defined as a species in danger of extinction whose survival is unlikely if certain threats continue operating, vulnerable species are believed likely to move into the endangered category in the near future if threats continue, and to be considered extinct the species has definitely not been located in the wild during the last 50 years (ANPWS 1991).
Extinctions and declines have not uniformly affected marsupial species. Terrestrial, medium-sized marsupials in the weight range of 35.0 g to 5.5 kg have proven to be more vulnerable, and omnivores and herbivores have declined to a greater extent than carnivores. Arboreal species such as possums and gliders and species that use rock piles for shelter have been less affected. Most problems with extinction and endangerment occur in the southern arid zone and the wheat belt of Western Australia; while the tropical north of Australia, the mesic northeast and coast of New South Wales, Tasmania, and numerous offshore islands have remained relatively unaffected by local extinctions (Short 1994).
Seven main hypotheses have been put forward to explain why species have declined and/or disappeared from various parts of Australia, and they include: 1) clearing for agriculture, 2) draining and salination of wetlands, 3) grazing and browsing by introduce animals, 4) changed fire regimes, 5) introduced predators, 6) disease, and 7) overkill by hunters (Kennedy 1992). By studying the history of threatened fauna and patterns of decline, experts have come to the conclusion that some of these hypotheses can be dismissed as not being a primary cause of declining populations.
For instance, there is no direct evidence that disease has led to any mammal extinctions, though epidemics have been blamed for the decline of carnivorous marsupials in southeastern Australia and Tasmania at the turn of the century. Though Aborigines and early European settlers hunted many species for food, there is also no evidence that overkill by hunters caused any excessive declines or extinctions. Kangaroos once were one of the most widely hunted marsupials, but remain so abundant today to be considered a pest. The case of the thylacine (Tasmanian tiger) possibly presents a debatable exception because this carnivorous marsupial was treated as wolves once were in North America-with zealous overkill. It is presumed extinct, but there have been supposed sightings of it in Northern Tasmania.
Clearing for agriculture obviously leads to local declines and disappearances of several species, but it is not considered a primary cause. Clearing has been confined to relatively small parts of Australia and few mammals were restricted to those particular habitat areas. Likewise, few species were restricted to wetland areas that were drained or salinized. The one exception to that is the Toolache wallaby of SE South Australia and SW Victoria for which swamps did form a significant part of its habitat.
Of course, any of the aforementioned factors can compound other existing problems, therefore contributing to the endangerment process. The remaining three hypotheses for marsupial decline/extinction are grazing/browsing by introduced animals, changed fire regimes, and introduced predators. These are indeed thought to be the main causes threatening marsupial survival--past and present. Exotic herbivores such as rabbits, goats, cattle, sheep, donkeys, pigs, and camels are abundant in Australia. Pastoralism is the main land-use in the arid zone, and many feral species extend into conservation reserves and unoccupied deserts. Their effect on the habitats of indigenous mammals that depend on the vegetation for food and shelter has been quite negative. Many arid zone marsupials depend on small habitat areas of exceptionally high quality, especially in times of drought, but these areas are often degraded by exotic herbivores, primarily rabbits. Various control mechanisms have been tried in the past such as introducing a virus into rabbit populations, but it only worked to reduce numbers temporarily because populations soon shot back up to problem levels again.
A second problem facing marsupials is an altered fire regime. Fire is an important modifier of habitat in Australia, but since European settlement fire regimes have changed significantly. Pre-European times were marked by several small fires occurring throughout the year. After settlement, this pattern changed to large, infrequent summer fires that had a homogenizing effect on the vegetation. Smaller fires left small patches of land in different stages of recovery, offering more habitat and food variety for the wildlife, as opposed to one large, less diverse area that can not support as much wildlife. Mammals could more easily outrun smaller fires to find safety, but larger fires more often trap and kill mammals. Studies show that the disappearance of mammals from Western Australia, NW South Australia, and SW Northern Territory coincide with the depopulation of Aborigines from the area, which led to the subsequent change in fire practice.
Also responsible for extinctions/declines are three exotic predators currently widespread in Australia. The dingo, a wild dog-like animal, is thought to have been introduced 3,000 to 8,000 years ago. It replaced the thylacine and tasmanian devil and commonly fatally attacks marsupials. Feral cats probably arrived around the 17th century form shipwrecks or visits by Asian fishermen and proceeded to cause the demise of several small marsupials and some as large as the rufous hare-wallabies. A third predator, the fox arrived much later between 1845 and 1865 in Victoria where it soon spread, colonizing most of the continent except the wet tropics by the 1930's. Foxes have been implicated in the decline and extinction of many native marsupial species. Poison in meat baits is often used to control the introduced predator population. Sodium monoflouroacetate (1080) works well because there is a natural occurrence of floroacetate in native vegetation so the native Australian animals have developed a tolerance for it and will not be harmed by it. Other population control mechanisms, especially biological controls that would immunize foxes against their own reproductive cells, are being researched in hopes of reversing the negative effect of intoduced predators on the native marsupials
Several scientists believe that climatic change has been responsible for extinctions in the past. They think that an increase in aridity about 20,000 years ago probably led to the disappearance of some 50 species of large Australian marsupials, known as the megafauna (ANPWS 1992). Evidence suggests that there will be another major climatic change in the future. In the past, species and ecological communities could adapt by shifting along environmental gradients, but today that would present a problem for many species because there are so many artificial barriers like cleared farmland and cities.
Now that we know the general reasons for marsupial endangerment and extinction, let us concentrate on one species, Phascolarctos cinereus, and examine the dangers it faces. The koala is a special concern for many; they would like to see its classification changed to endangered so it would be offered a higher level of protection. It is not that the koala is in any more danger than any other marsupial species, but more popular attention is devoted to the koala--it is a national icon for Australia that draws tourists. Many people outside Australia have the idea that the country is heavily populated with koalas, but most Australians have never even seen a koala in the wild-only in zoos. No one really knows exactly how many koalas remain because of their secretive, nocturnal behavior. The Australian Koala Federation suggests that numbers have dropped from 400,000 in the mid 1980's down to between 40,000 and 80,000 today (Stix 1995). Humans are their principal predator.
With the arrival of Europeans, it became widely known how easily koalas could be caught because of their characteristic slowness. Millions were hunted and killed for their fur. By 1889, 300,000 skins a year were sent to London as "cheap and durable" fur. When it became known that some 500,000 koala furs were being sent to St. Louis every year, the U.S. public responded with outrage and disgust. In retaliation, President Herbert Hoover signed an order permanently prohibiting importation of koala and wombat skins (Phillips 1994). As demand gradually died down, most of the hunting stopped. The last open season for koala hunting was in 1927. In 1930 the koala had become extinct in South Australia, but thanks to reintroduction efforts it can again be found there today.
Now koalas face many other dangers such as cars, dogs, and deforestation. An estimated 80% of natural koala habitat has been destroyed (Anderson et al. 1998). Destruction of habitat and corridors creates significant stress and danger for koalas. They are extremely picky eaters, preferring less than a dozen of 650 native types of eucalyptus (Stix 1995). Usually they jump from tree to tree looking for choice leaves, but when the forests are thinned and destroyed they have to march along the ground searching for food trees, sometimes great distances. This presents the risk of being hit by automobiles. Because they are nocturnal they have poor eyesight when confronted with a bright light--like the headlights of a car, plus their gray coloring blends in well with the road. Out of 4,000 koalas reported killed yearly, 2,500 victims are hit by automobiles (Payne 1995).
Urbanization around koala habitats is a real problem. Dwindling colonies become separated by houses, fields, golf courses, shopping centers, and roads allowing for isolation which leads to inbreeding which threatens to impoverish the genetic stock of the species. Loud, abrupt noises frighten these marsupials and can lead to chronic stress which makes them unhealthy and more prone to disease. Swimming pools, another part of urbanization, are prove dangerous for koalas because when constructed in the path of former food tree corridors, they will maintain a straight path, falling right into the pool. Koalas are able to swim but usually end up drowning because they can not get out. Residents can help the situation by attaching a rope to poolsides so they have something to grip in order to climb out.
With urbanization one also finds pets. Dog attacks on koalas are a real problem and are often fatal. Physically, koalas are suitably equipped with claws to fight back, but they have no experience with the need for self-defense for lack of natural predators. Also, they have undersized adrenal glands so they do not have the strong fight-or-flight reaction typical of other mammals.
As if these problems were not enough, koala populations are plagued by a pathogenic intracellular bacteria known as Chlamydia psittaci. The major site of chlamydial infection is the reproductive tract, resulting in infertility for females. Other chlamydial lesions often lead to reduced life expectancy. In some cases chlamydia is the enemy because it reduces populations already on the edge, but on the other hand, it can act as an effective natural control among populations that have gotten too large to remain healthy.
It is interesting to note that saving dwindling koala populations is not a problem in all parts of Australia. Some koala populations have a high potential rate of increase. In continuous forest, koalas are able to disperse from defoliated sites, but on islands or isolated patches of forest the severe defoliation of food trees results in malnutrition and mortality. Since the 1920's it has been practice in Victoria to remove koalas from islands where trees show evidence of too much defoliation and release them in mainland forests (Lee 1991). This helps keep island populations under control while reestablishing koalas to some of their former range. But there are two problems with this translocation procedure. One, there is a shortage of suitable sites for the release of koalas; and two, introducing chlamydia-free koalas into populations with common cases of chlamydia is dangerous to their health. New approaches must be made. For example, on Kangaroo Island experts want to solve the overpopulation problem by developing sterilizing techniques instead of translocating the koalas. A few people are in favor of a culling technique, but it is unlikely that koala-lovers will allow that to happen anytime soon.
Today there are several groups working to save the koala. The Koala Hospital, founded in 1973, takes care of sick or injured koalas that people find. More and more research is being done on koala medicine and habitat thanks to fund-raising efforts of groups like the Australian Koala Federation (AKF), National Parks and Wildlife Service, and Koala Preservation Society of New South Wales. The AKF recently began a "Koala Habitat Atlas" project in which researchers use GIS technology to identify, map, and rank koala habitat so land-use planners can make informed decisions that will not hurt existing koala populations (Anderson et al. 1998).
In general, conservation efforts have increase dramatically this century in Australia. Islands are playing an important part in marsupial conservation. At least 62 marsupial species occur on 160 islands around the Australian continent; seven mainland species, the eastern quoll, carpentarian antechinus, western barred bandicoot, burrowing bettong, eastern bettong, banded hare-wallaby, and red-bellied pademelon, are now only found on islands. Though some of the islands have been affected by the same factors that led to mainland extinctions--exotic species, timber harvesting, changed fire patterns--most are unaffected and remain as refuges for threatened species.
Tasmania became a refuge for the Tasmanian devil and the thylacine when dingoes replaced them on the mainland. The red-bellied pademelon, eastern bettong, and eastern quoll also found a safe haven there when their mainland populations became extinct. The important thing about Tasmania is that foxes are not established there, though feral cats are present. The three Western Australia islands of Barrow, Bernier, and Dorre are of great conservation importance because four of the most threatened marsupials--western barred bandicoot, burrowing bettong, mala, and banded hare-wallaby are found there. Islands can be used to build a population back up in order to successfully return a species to the mainland someday; and surviving island populations can be used to study island biogeography, ecology, and threatened species biology.
Some marsupial species are part of management plans under the Commonwealth Wildlife Protection Act of 1982 or under separate state/territory legislation. Almost all marsupials are protected within all states and territories of Australia, though specimens can be taken with the proper permit. Five species of kangaroos and large wallabies and the common brushtail possum are currently allowed to be killed as pests to reduce damage or for use in commercial industry. At the Federal level, the government established an Endangered Species Program which includes a program termed "National Strategy for the Conservation of Species and Habitats Threatened with Extinction" (Kennedy 1992).
The Australasian Marsupial and Monotreme Specialist Group works to identify threatened species and causes and through cooperation with other concerned groups develops management strategies and priorities for conservation efforts. Two national organizations have also contributed to marsupial research and management programs-the Australian National Parks and Wildlife Service (ANPWS) and World Wide Fund for Nature Australia.
Zoos also support a range of endangered species programs through maintenance and breeding of mammals in captivity. Australian zoological institutions often collaborate with wildlife agencies on specific conservation programs. Also, the number of conservation reserves and wildlife parks is steadily increasing.
With ongoing education and conservation efforts, the future looks hopeful for Australia's threatened marsupials. "Because most Australian species are found nowhere else in the world, we have a social responsibility to conserve them" (ANPWS 1992). To lose any of these wonderfully unique species would be a tragedy. Ken Walker, Aborigine elder, says of today's conservation efforts, "The people of the earth are starting to wake up. They've taken enough away" (Payne 1995).
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