This is a story of arid Australia. It is part of the harsh, desert beauty of red sand and of weather-beaten rock, of spinifex, saltbush and of desert sheoak. Some parts of the story are like tracks in sand. We know some of what has passed but already the full story is lost. It is a story of earth, fire and water; of the scarce nutrients in ancient, eroded soils, of the pattern of fires and of rain and the vegetation that these produce. It is the story of foxes and cats, of lack of water, food and shelter, death and extinction. It is the story of the last 200 years in arid Australia where there has been a massive loss of native animal species.
About half the land mass of Australia is arid land. Twenty-eight non-flying arid species of mammals are endangered or extinct. To this can be added other species, such as the brush-tailed possum, which are still common in coastal areas but which have become extinct or endangered in the arid areas. This catastrophic decline has no modern parallel in other continents. It is a uniquely Australian event which has taken less than 200 years - a millisecond in geological time. Aboriginal people have been aware of this decline but have been fighting their own battle for survival. Other Australians are only now beginning to understand the extent of the arid lands tragedy.
Prolonged droughts are normal in arid regions. At the end of long droughts surface water and food are restricted to isolated refuge areas. In times of prolonged drought many desert mammals are thought to have either died or retreated to refuge areas.
One theory is that these refuge areas were special because there was extra run-off water from rocky hills. In some cases refuges were formed where the ground water tables were close to the surface. Often, because of the runoff, the soil in refuge areas was slightly richer in nutrients. Extra water and nutrients create small oases where mammals could survive during droughts. With the return of the rains, desert dwellers would radiate from the refuge areas. In this way desert animals survived hundreds of severe droughts over many thousands of years.
Unfortunately, cattle, donkeys, camels and rabbits were also attracted to refuge areas. They ate the vegetation and what they did not eat, they often trampled. They fouled the waterholes. Their hard hooves cut up the soil and created erosion, filing the waterholes. The delicate balance between desert plants and plant eaters, forged over millennia, was shattered.
One fire looks much the same as the next but the similarity often hides significant differences. The difference between fires, and patterns of fires is the difference between survival and extinction for many desert mammals. Animals depend on plants and many Australian plants depend on fires of a certain temperature, or fires at a certain time of year in order for seeds to germinate. Too frequent fires can cause some plants to disappear. Mulga, a very important arid plant, is an example. This shrub dies when burnt. The seeds germinate after fires and new stands of mulga appear. If another fire occurs before the young stands of mulga have had the chance to develop seed, then mulga disappears from the area. Fires which are too infrequent enable fire sensitive plants to crowd out other plants thus reducing species diversity in a particular area. It is now considered likely that much of the pattern of vegetation which existed in Australia in 1788 was the direct result of a pattern of fires which Aboriginal people lit deliberately as well as those caused by lightning.
In arid areas, the complex pattern of patch burning developed by Aboriginal people created a patchwork of areas of older vegetation and areas of vegetation with different food plant species, fresh shoots and vigorous young growth. The desert animals frequently used patches of older vegetation for shelter and fed on the patches of young vegetation.
The patch burning ceased when Aboriginal people were driven from their traditional country. Fuel built up and huge wildfires swept over vast tracts of the arid country. Mammals which had developed a delicate balance with a patchwork of vegetation were either destroyed by the huge fires or found that the huge tracts of single-age vegetation no longer provided the variety so necessary for their continued survival.
Some of the desert species are still struggling for survival. Although extinct on the mainland, some species survive on small isolated islands off the coasts of Western Australia and South Australia. They have not had to deal with introduced foxes, cats, cattle, donkeys, camels and rabbits. The burrowing bettong and the banded hare- wallaby are examples.
Other species survive on the mainland, often in small isolated populations, which have somehow escaped a fatal combination of circumstances.
Some mammals have had an assisted passage to survival. The mala, or rufous hare- wallaby, has been bred in captivity by the Conservation Commission of the Northern Territory (CCNT). Its habits and habitat have been studied by scientists. Aboriginal people have given vital information on behaviour, habitat needs, and the appropriate fire patterns required to maintain suitable habitats. Based on this information, a cooperative attempt is being made between the Commission and Aboriginal people to re-establish the mala in the Tanami Desert. Partly funded through the Federal Government's Endangered Species Program, it is too early to tell how successful this recovery project will be.
In the 1970s there was increasing concern that the range of the numbat was dwindling. Scientists from the Western Australian Department of Conservation and Land Management studied the biology of the and showed that a big threat to the survival of this species is predation by foxes. Despite adequate food and shelter, despite breeding amble young to reproduce the species, the numbat could not replace the large number of individuals being taken by foxes. The species was in decline. Experiments with fox control showed that numbat numbers climbed quickly once foxes were removed.
In less than two hundred years since 1789 there has been a catastrophe. We are unsure exactly why each of the extinct species died out. For some the only traces are in museums and in the memories of old Aboriginal men and women... the last people to know them from seeing them alive in the wild.
We do know that mala, the rufous hare-wallaby, can survive in the desert provided the area is burnt in the traditional Aboriginal way; and there are no rabbits and foxes. We are becoming increasingly certain that the availability of nutritious food during times of drought stress has also been critical.
We know that some of these mammals are gone forever. Some of them were ordinary and some beautiful but each was a unique part of our natural heritage.
On the other hand we know that some mammals which are on the brink of extinction can be saved.
Scientists believe thatdingoes were brought to Australia at least 15 000 years ago by Aboriginal people. Although it is not certain, it is believed that dingoes had an impact on the native animals. For example, thethylacine (Tasmanian tiger) and the Tasmanian devil disappeared from mainland Australia but survived for much longer in Tasmania where dingoes were absent. The surviving desert animals have had about ten thousand years to adjust to dingoes. By 1788, a new balance had been achieved.
The introduction of cats and foxes fatally altered this balance. Some species simply fell off the scales and disappeared forever. Others maintain a precarious grip. Some mammals which have become extinct on the mainland survive quite well on islands. These islands do not have introduced foxes, cats and rabbits.
It is painful to think about some of the arid mammals which have become extinct in our lifetime. For some we have beautiful illustrations by the early naturalist John Gould. The illustrations capture the light earthy colours so typical of many of the arid animals; their bright eyes and alert stance give a hint of quick, sure movement. But now they exist only in books. Examples of extinct desert mammals are the lesser bilby, the pig- footed bandicoot, and the central hare-wallaby.
A feature of the story is that 90 per cent of all mammal species with adult body weights between 35 and 5 500 grams are either extinct or endangered. It has paid desert mammals to be big or small but not medium. Why? The short answer is that we do not know for sure. One theory is that mammals which weighed less than 35 grams could survive in smaller-scale habitats and somehow missed the general destruction created by introduced animals and alterations to the fire patters. Larger mammals have the capacity to move along distances to surviving patches of habitat, as well as being too large for foxes and cats to attack.
Extinct: Species not definitely located in the wild during the past 50 years.
Endangered: Species in danger of extinction and whose survival is unlikely if the causal factors continue operating.
Vulnerable: Species believed likely to move into the‘Endangered’ category in the near future if the causal factors continue operating.
For many desert mammals there is no happy ending to this story. They are gone. The quality of our lives has been diminished by the loss of the rich variety of animals. For the survivors, it is now a story of a race against time and circumstances. We are in a position to alter those circumstances. We can tip the scales one way or the other.
Whether desert mammals survive, depends on the choices we make. We can make choices through governments by making laws to protect and conserve; through conservation agencies by making and carrying out management choices; through non-government organisations by increasing awareness and support for appropriate action;
and as individuals by choosing to consume less in order to put less pressure on the environment. We know that the choices are often difficult to make but we also know that all choices count.
We can choose:
In response to the crisis, the Commonwealth Government has taken a number of steps:
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