Australian Bilby Appreciation Society
Mr Bilby can take you
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article by Peter McRae
One can ponder the significance of almost anything while relaxing in an old cast iron bath. Most people can only imagine what it's like to do so while sitting in the middle of 2,300 square kilometres of virtually treeless paddock, but take it from me, with a view of the vast Mitchell grass plains extending for 360o around you it's a wonderful experience. And this also happens to be one of the very few locations where the Greater Bilby survives in reasonable numbers. Rob Atherton, a fellow bather, friend and former colleague, dubbed the Bilby the 'gentleman of the inland plains' and, the pleasure of the bathing experience aside, it is this pretty little marsupial that has drawn us to this place.
The view from the bathtub is typical Queensland Bilby habitat. The romantic western towns of Birdsville, Betoota, Bedourie and Boulia surround seemingly endless, undulating plains of Mitchell grass and salt bush that stretch west from the flood plains of the Diamantina River to the fringes of the Simpson Desert dunefields. These plains are dissected by a myriad of drainage systems that form part of the channel country of south western Queensland.
Here Bilbies dig burrows up to two metres deep in the red-brown soils and in the process deposit a substantial amount of paler subsoil in a characteristic fan-shaped mound about the entrance. This feature is obvious from the air and may remain visible for years after the burrow has been abandoned. But to ascertain present occupancy one has to assess burrows on the ground. Those that are occupied are quite distinct and numerous faecal pellets, feeding scrapes and tracks generally indicate an animal's presence. Other mammals and reptiles that dig and utilize burrows in the same area are not as energetic and fastidious in their excavations.
An extensive former range
No substantial populations of Bilbies were located during the Diamantina Shire fauna survey, a massive and intensive search conducted between 1981 and 1985. This alarming situation prompted two detailed studies to discover its whereabouts and status and, with funding from Delhi Petroleum and the World Wildlife Fund, the Bilby's decline in approximately 90% of its former range was documented.
Evidence of extensive past occupation is provided in many ways: historical records 'from early explorers and settlers, museums and old burrows and depressions still visible in the landscape. Consider the words of H.H.Finlayson in 1936 "...in parts of the country thousands of acres of loamy mulga flats have been closely harrowed by its scratchings in search of beetle larvae, which occur there." Or of Baldwin Spencer, who in 1896 wrote of the Bilby ".. not uncommon, judging by the number of tails used by the natives as ornaments. They tie the white terminal tufts together in bundles of from twelve to twenty."
The local knowledge of long-term residents has also been invaluable. Gordon Robinson of Canary Station near Boulia recounts how, as a kangaroo shooter in the 1960s, he used to regularly see six to eight Bilbies a night on Springvale Station. Gordon's son Charles is a ranger at Diamantina Lakes National Park. A wily and observant character known to the world as 'Chook', he told me a similar story of Bilbies near Boulia in the 70s and 80s. These areas no longer support Bilbies and today tell-tale fans of differently coloured soils scattered across the plains are the sorry legacy of past occupation.
I have had the good fortune to be involved with the Queensland project since its inception in 1988. Our research has not only attempted to understand the Bilby's dramatic decline, but also to find out what can be done to arrest and perhaps reverse it. We have been gathering basic but valuable biological and natural history data which are sorely lacking. This is all the more surprising given the Bilby's former abundance.
About the size of a rabbit, Bilbies move with an unusual 'half-hopping' gait and, like rabbits, they have huge ears. We don't really know the function of this structural peculiarity. Is it for thermo-regulation? Or for very low or very high frequency communication that is inaudible to humans? Their ears do not seem to be important in locating food, but this is perhaps not surprising because they are omnivorous and half of their food doesn't make a noise anyway! On the other hand, their sense of smell appears to be well-developed and they move about with their long, pointed noses to the ground as they search for tasty subterranean morsels including spiders, bulbs and a variety of insects and their larvae. Once these are located, furious digging ensues and active burrows are usually surrounded with a pock-marked area of feed scrapes up to 25cm deep. Beetles and grasshoppers are frequently caught above the ground and one animal was seen chasing a moth.
Like many animals, they establish a home range where they carry out all the activities of being a Bilby, such as eating, sleeping and reproducing. The size of home ranges varies between sexes and they may even overlap, but 6-10 burrows are usually maintained in each. There is generally only one occupant per burrow, although females may share with young for a short period of time. Females tend to use only one or two for sleeping during the day, whereas males frequently use four or five, the others probably serving as escape refuges if a predator, such as a Dingo, upsets the nightly foraging routine. Greater Bilbies reportedly close off or back fill their burrows some 50-100cm from the entrance in response to predators, and the now extinct Lesser Bilby is said to have closed its burrow behind it at the surface. Whatever the case, it is unusual behaviour - I haven't observed them doing the former and I've seen the latter performed only once, by a radio-collared animal.
These beautiful little animals are strictly nocturnal. I have never seen them emerging from their daytime retreats until it is dark and most don't emerge until several hours after sunset. Similarly, 'bedtime' usually occurs a couple of hours before the first hint of light in the eastern sky. Strong winds, heavy rain and a full moon all reduce above-ground activity, but light rain appears to stimulate 'housekeeping' and it is a good time to observe animals as they clean out their burrows during showers.
What has caused the decline?
Steve attributes the decline of the medium-sized mammals in and areas mainly to the loss of mosaics of vegetation types that once provided refuge areas of high nutrients in hard times. This loss of 'habitat patchiness' was largely brought about by the explosive invasion of rabbits in the late 1800s. Rabbits reduced ground cover, plant availability and diversity, a situation that was exacerbated by grazing livestock and changing fire regimes -or a lack of fire. The CWR mammals ended up with no access to local refuges and, being less mobile than the larger mammals and birds, couldn't move further afield. The crunch came when the European Fox wandered inland, probably on the heels of the rabbit invasion, and cleaned up the remaining small populations of native mammals along the way. Feral cats have also had an impact on the smaller species and juveniles of the larger species.
But so far we have been unable to establish the precise cause of the Bilby's decline. A National Recovery Plan funded by the Australian Nature Conservation Agency (ANCA) is investigating Bilby conservation, applying different research and management actions in each area to reflect their different needs. Other actions include genetic analysis, disease and parasite screening and maintenance of captive breeding colonies. Meanwhile, we must apply the four R's to Bilby conservation:
Research. It is imperative that we continue and expand research on the population dynamics of the Bilby in all states where it still occurs. We must understand the processes involved in its decline with the aim of reversing them in areas where this is still feasible.
Reserve. In the Northern Territory Bilbies occur only on Aboriginal land. In Western Australia they are scattered in pockets over a wide area on Aboriginal land, and unknown numbers are protected by the Gibson Desert and Percival Lakes Nature Reserves and Rudall River National Park. In Queensland the handful that live in the Diamantina lakes National Park are not considered a viable population. Protracted negotiations over the past five years between Stanbroke Pastoral Company and the Queensland Government appear to be finally bearing fruit and it is hoped that part of Davenport Downs, a Stanbroke property straddling the Diamantina River and containing a substantial proportion of this population, will soon be gazetted as National Park.
Re-introduce. One of the aims of the National Recovery Plan is to re-establish Bilbies in areas where they formerly occurred. Plans are under way to re-introduce captive -bred animals into a number of national parks in western Queensland. The control of feral predators and competitors will be a vital part of management if these projects are to be successful.
Re-educate. If we are fair dinkum about saving and re-establishing Bilbies as an integral part of the rural landscape, we need to encourage people to think differently about the intrinsic value of our unique faunal and floral communities. People must re-evaluate their attitudes to the costs and benefits of primary production in certain areas and consider the importance of ecological sustainability and maintaining the integrity of these landscapes.
Baths, bunnies and Bilbies - a conundrum
Although a contributing factor, cattle alone haven't caused the decline of the Bilby. Rather, it is a combination of several factors, including overgrazing, rabbits, foxes and cats. Continual and heavy grazing just pushes the already delicate balance a little further. I guess in some ways the Bilby is one of the lucky ones. It survives precariously, thanks in no small part to its omnivorous diet, burrowing nature, reproductive output and the fact that foxes haven't yet managed to scour every square inch of inland Australia.
The Easter Bilby