Guarding vulnerable Australian species
In Ronald Strahan’s revised edition of The Mammals of Australia, C. H. S. Watts describes the plains rat as among “the loveliest of Australian rodents”. While its loveliness might be in the eye of the beholder, it’s certainly among the most tenacious, being adapted to some of the driest, most inhospitable country: the stony gibber deserts and cracking clay soils of the Lake Eyre Basin.
There, it can survive without drinking, obtaining water from food starches, aided by its highly concentrated urine and absence of sweat glands. During the day, colonies shelter from predators and the intense heat in complex burrow systems that can be more than 40 kilometres long, yet separated from each other by only a matter of metres, interconnected by runways on the surface.
Not that water is a problem for the plains rat right now. Surveys at Andado Station, a cattle property in the south-east of the Northern Territory abutting the western edge of the Simpson Desert, are showing a spike in numbers following unseasonal winter and spring rains. And it’s places such as Andado, and animals like the plains rat, that are helping prompt a rethink of how we might save what is left of our desert fauna.
It’s well known that Australia has one of the worst mammal extinction rates in the world, with 30 species – more than 10 per cent – lost since European settlement. Many more are at imminent risk of extinction. What might seem unusual is that most of those extinctions have occurred in our remote areas, far from the major urban centres of the eastern seaboard.
Cats and foxes take much of the blame, but the causes of the ecological catastrophe are multifaceted. Changed fire regimes are a big problem, so too overgrazing, not only by cattle but feral herbivores including rabbits, goats and camels. But there’s another, more subtle factor at play: in a country of climatic extremes, our native fauna often rely on small pockets of the landscape in which to take refuge during drought.
Once, the plains rat (Pseudomys australis) was thought to be far more widespread, from the western slopes of the Great Dividing Range straddling Queensland and New South Wales, and from the Nullarbor east all the way to the mouth of the Murray. It’s thought to have declined by up to 90 per cent since European settlement, and it’s nationally listed as vulnerable under the Environment Protection and Biodiversity Conservation Act.
Andado – where the gibber plains of the Lake Eyre Basin, the sand dunes and spinifex of the Simpson Desert and the runout of the Finke River all intersect – is a plains rat refuge, a place where it has always survived through the bleakest times. It booms and busts according to prevailing conditions; at least some of the historic records from further afield were probably never an indication of stable populations.
Many of our arid-zone animals and birds have existed this way forever. The flock bronzewing, a pigeon that still occasionally darkens desert skies in aggregations of hundreds of thousands, is one. The long-haired rat is another, and the letter-winged kite – the world’s only nocturnal hawk – follows its periodic irruptions: as the rats spread, only to die off as conditions return to normal, so too do the kites.
It follows, then, that if a refuge is excessively degraded or disturbed, we go a long way to wiping out the animals that depend upon it, too. The difficulty is in identifying these areas. A refuge may be not much more than a dot on the map. It has taken a century, for example, to locate a stable, apparently sedentary population of the night parrot, long believed extinct. And refuges vary from species to species.
Dr Diana Fisher, a fellow at the University of Queensland’s school of biological sciences, is trying to map where these areas are. She points out that a species refuge “might not look much different to the rest of the landscape, but there’s something about it that protects them, not just from the dry conditions, but also predators and disease”.
Finding out where feral predators themselves eke out a living during bad times is helpful, too. “Cats are very good at surviving in the desert, but they have some limitations where they don’t do as well with very hot conditions,” Fisher says. “They have to find a refuge themselves, so finding where [they are] might enable us to use that information to control them.”
Non-government organisations such as the Australian Wildlife Conservancy have had some success creating their own wildlife refuges: heavily fenced areas, purged of feral animals, with surviving populations of native fauna such as the woylie, a species of bettong, reintroduced from other areas, in miniature simulacrums of what the Australian landscape might once have looked like.
“There is now consensus at a policy and scientific level that a network of feral predator-free areas are required,” says Atticus Fleming, chief executive of the conservancy. He points to the bilby. “The bilby now lives in less than 5 per cent of its original distribution and the population’s estimated at less than 10,000,” he says. “About 15 per cent of the world population is on AWC land in feral predator-free areas.”
Again, feral predators are only one part of a more complex picture. While the bilby needs all the help it can get to survive in Queensland’s Channel Country, it seems to be comfortably outlasting cats in the even more inhospitable Great Sandy Desert of Western Australia.
Different stressors on different species rarely work in isolation. “We’ve already lost a lot of things – [many of] the bandicoots [including the bilby] and that sort of range of animals have gone, but defining what the disturbance would have to be to make those things disappear is the tricky one,” says Alistair Stewart, a fauna scientist with the Northern Territory’s Department of Environment and Natural Resources.
Occasionally, it might be more straightforward. “There is potential for mining to be so selective that it could have a devastating effect – the footprint size of an open-cut mine could encompass one of these entire refuges,” Stewart says. Generally, though, that’s a bigger danger for our microfauna – hidden, less mobile invertebrates such as land snails – than it is for mammals and birds.
Refuges also might not function as well as before. They may be degraded by overstocking. In drought, the better-watered parts of the landscape support livestock as well as wildlife, putting pressure on smaller, less genetically diverse populations. And animals that disperse after rain are more easily wiped out by predators elsewhere. The result is that the booms aren’t as big and the busts are longer lasting.
The letter-winged kite is one species that has suffered, undergoing an almost imperceptible decline over the past 30 years. This graceful raptor breeds in colonies mostly in the Strzelecki and Diamantina River systems, dispersing across the continent during boom times. Now it is rarely seen outside its core range: cats have been observed in the bird’s nest trees, wiping out chicks and stifling population growth.
Not all of our fauna operates like this and not all refuges are climatic. Mountains and areas of rocky scree serve the same function. Fire doesn’t spread so quickly and it’s easier to make a quick escape from predators. In the MacDonnell Ranges west of Alice Springs, the black-footed rock wallaby is locally common, whereas a subspecies in the West Australian wheat belt is in dire trouble.
Mark Carter, an Alice Springs-based ecologist and guide, says animals such as the long-tailed dunnart – which truly is one of our loveliest marsupial mice, with a jauntily crested tail more than twice its body length, thought to be used as a balancing rod – might once have been far less strict in terms of its habitat requirements, but now survives in only the most rugged parts of the landscape.
Fisher backs this, saying there is evidence that there are few predators in rocky areas. “That’s a protective thing, perhaps, for things like rock wallabies and northern quolls. And also maybe it’s a better fire environment. But we’re not sure yet if it’s just the rugged habitat – there are fewer cats, and it’s easier for the animals to escape – or if there’s more vegetation, because the fire doesn’t get in there as much.”
The key point, Carter says, is that these safe havens are often not in the form we imagine and not where we might imagine them to be. “The one thing they’ve all got in common is that they’re extremely vulnerable. It wouldn’t take much to just completely wreck them for the animals that are so dependent on them.”
This article was first published in the print edition of The Saturday Paper on Dec 3, 2016 as "Know an ark ". Subscribe here.