Wildlife Australia, December 1996
ISBN 0 6422 1395 X
Conservation of Marsupials and Monotremes in Australia
This Action Plan reviews the conservation status of 209 taxa of Australian monotremes and marsupials: one species and three subspecies of monotremes and 112 species and 93 subspecies of marsupials.
For taxa with extra-limital distributions (e.g. Sminthopsis archeri and Phalanger intercastellanus) we have allocated conservation status only on the basis of their Australian distribution and abundance. (Allocation of IUCN categories to these taxa for the 1996 Red Book took account of their total range, see below.)
Australia accounts for about one third of the world's mammal species that have become extinct in modern times (Groombridge 1993). Within the marsupials, ten species and six subspecies are presumed to be extinct (Table 2) and many other taxa have declined drastically in range and abundance. Some 6.5% of marsupial species or 8% of marsupial species plus subspecies are extinct. Neither species of Australian monotreme is considered to be threatened; however, one subspecies of the echidna is listed in this Action Plan as Vulnerable.
|Thylacine, Thylacinus cynocephalus
Desert Bandicoot, Perameles eremiana
Pig-footed Bandicoot, Chaeropus ecaudatus
Lesser Bilby, Macrotis leucura
Broad-faced Potoroo, Potorous platyops
Desert Rat-kangaroo, Caloprymnus campestris
Eastern Hare-wallaby, Lagorchestes leporides
Central Hare-wallaby, Lagorchestes asomatus
Crescent Nailtail Wallaby, Onychogalea lunata
Toolache Wallaby, Macropus greyi
|Western Barred Bandicoot (mainland), Perameles bougainville fasciata
Eastern Bettong, Bettongia gaimardi gaimardi
Boodie (mainland), Bettongia lesueur graii
Brush-tailed Bettong (SE mainland), Bettongia penicillata penicillata
Rufous Hare-wallaby (SW mainland), Lagorchestes hirsutus hirsutus
Banded Hare-wallaby (mainland), Lagostrophus fasciatus albipilis
Australian mammal extinctions may have been worse than current statistics indicate, as some species probably became extinct before being recorded by naturalists and/or before their full geographic ranges had been delineated. The Kuluwarri or Central Hare-wallaby (Lagorchestes asomatus), for instance, is known to science from only a single skull but apparently had a widespread arid zone distribution within living memory (Burbidge et al. 1988). Sub-fossil deposits have revealed several mammal species that probably were extant at European settlement, including an unnamed potoroid marsupial from the Nullarbor Plain (Baynes 1987). At the subspecies level, taxa other than those listed in Table 2 may be extinct taxonomic boundaries within some of the extinct species are unclear and may never be fully elucidated because of lack of specimens. The Tasmanian Pademelon, for example, is extinct on the Australian mainland, but there have been no studies to clarify the taxonomic status of this population, and a number of mainland taxa of the Western Barred Bandicoot (Perameles bougainville) have been described, but the real number may never be known.
The above national estimates do not show the degree to which increasing numbers of species are under pressure regionally. Marsupial declines have occurred at different rates in different parts of Australia; this is discussed below.
Some taxa have suffered enormous changes in range and abundance. The Burrowing Bettong or Boodie (Bettongia lesueur), for example, once inhabited more than 50% of the Australian mainland but now occurs naturally only on three islands off the Western Australian coast, with a total area of only 330 km2. The mainland subspecies is extinct. Other declines have been similarly dramatic: Rufous Hare-wallaby (Lagorchestes hirsutus) from about 25% of the continent to two small islands (two separate subspecies), captive populations representing one of the mainland subspecies, and an experimental re-introduction, comprising very few animals, of the same subspecies; Woylie (Bettongia penicillata) from more than 40% to less than 1%; Chuditch (Dasyurus geoffroii) from about 60% to less than 2%; and the Numbat (Myrmecobius fasciatus) from about 25% to less than 1%.
Some taxa are now extremely rare: the Northern Hairy-nosed Wombat (Lasiorhinus krefftii) has been reduced to about 67 individuals, of which possibly only 15 are breeding females, while the central Australian subspecies of the Mala (Lagorchestes hirsutus central subspecies) became extinct in the wild in 1991 and now exists as about 150 animals in captivity and as one experimental re-introduction, which consists of only about 10 wild animals.
While marsupial conservation is currently a major cause for concern in Australia, there have been considerable advances in recent years. Taxonomic research, often using new genetic research technology, has improved our knowledge of conservation unit boundaries, knowledge of species' ecology is growing rapidly, there is a developing science of threatened species management and there is heightened interest in nature conservation in the country. Commonwealth, State and Territory nature conservation agencies are embarking on or coordinating Recovery Plans that include habitat management, population protection and management, exotic predator control and translocations. Research into the abatement of several threatening processes is underway and some research results have been applied, e.g. about 900 000 ha of conservation lands in the south-west of Australia are now subjected to routine fox control, mainly to protect threatened marsupials.
Historical causes of decline and extinction
Before successful management programs can be applied to a threatened species, the factors that caused the initial and/or continuing decline must be identified and counter methods devised. For many species there are insufficient biological and historical data currently available to identify confidently the reasons for their threatened status, and a recent trend has been to examine whole faunas rather than wait for detailed single species studies to be completed. Burbidge et al. (1988), Burbidge and McKenzie (1989), Johnson et al. (1989) and Morton (1990) all discuss the possible contributing causal factors, and how singly or in synergistic combination, they have led to the extinction or decline of marsupial species.
Critical weight range species
Many authors have noted that, in Australia, the non-flying, medium-sized mammals have been particularly affected since European settlement (e.g. Calaby 1971, Morton and Baynes 1985, Giles and Lim 1987, Morton 1990). Burbidge and McKenzie (1989) have shown that extinctions and declines are virtually confined to non-flying mammals with mean adult body weights between 35 and 5 500g (noting that the decline of the Western Brush Wallaby Macropus irma suggests that the upper limit should be extended to about 8 000 g). Variation in patterns of attrition within this critical weight range (CWR) can be explained almost entirely by a combination of regional rainfall and, to a lesser extent, species' habitat and dietary preferences. CWR mammals in greatest danger of extinction are from arid and semi-arid areas. Those species confined to the ground's surface are in most danger and herbivores and omnivores are more likely to become extinct than carnivores. CWR mammals that have declined or become extinct are not restricted to one phylogenetic group but include species from most families of marsupials as well as native rodents.
Eight of the ten extinct species and all six the extinct subspecies of marsupials were CWR species. Of the 56 marsupial taxa listed as Extinct in the Wild, Critically Endangered, Endangered or Vulnerable in this Action Plan, all but six lie within the CWR.
Causal factors in historical decline
Causal factors were discussed extensively in the 1992 Action Plan (Kennedy 1992). In summary, most authors agree that the introduction of exotic predators, especially the European Red Fox (Vulpes vulpes) and Feral Cat (Felis catus), the introduction of exotic herbivores, especially the European Rabbit (Oryctolagus cuniculus), Sheep (Ovis aries) and Cattle (Bos taurus), and changed fire regimes, particularly in the arid grasslands, have contributed to the decline and extinction of an array of species in Australia. There is little or no evidence to suggest that overkill by hunters (except on islands), disease, or drainage and salination have been the prime cause of extinction of suites of species.
Land clearing has been the major factor in the demise of one species and the decline of others. The Toolache Wallaby (Macropus greyii), one of two non-CWR species that is extinct, occurred in the south-east of South Australia and the south-west of Victoria. Robinson and Young (1983) have reported that swamps formed a significant part of its habitat and that most of them have now been drained in a series of schemes that commenced as early as 1862. They concluded that habitat destruction, including clearing of vegetation and drainage, was the major cause of the demise of the species. Land clearing has also greatly affected the Northern Hairy-nosed Wombat (Lasiorhinus krefftii), the Eastern Barred Bandicoot (mainland) (Perameles gunnii unnamed subspecies) and the Prosperpine Rock-wallaby (Petrogale persephone). Thus, while land clearing has reduced the range of many species and is contributing to current declines, it has probably been the primary cause of extinction of only one.
The other Extinct non-CWR species is the Thylacine (Thylacinus cynocephalus). Extinction in this case has been attributed to over-hunting and habitat destruction; although disease may have contributed (Smith 1981).
In summary, it appears that the interaction of three factors changes to habitat caused by introduced herbivores, homogenisation of habitat following changed fire regimes and, particularly, the spread of exotic predators has been mainly responsible for the high extinction rate of marsupials since European settlement of Australia. Habitat clearing has also affected the extent of occurrence of many species.
Regional differences in marsupial decline
Marsupial declines have occurred at different rates in different parts of Australia.
The greatest decline has occurred in the arid regions where approximately 33% of mammal species are locally extinct in sandy and stony desert ecosystems (Burbidge et al. 1988, Burbidge and McKenzie 1989), including six of the ten extinct marsupial species. This is the highest regional extinction rate in the country and it has occurred without significant impact by agriculture, pastoralism or mining on most of this very large region.
In semi-arid lands there have also been high levels of extinctions and decline. Heavily cleared semi-arid lands have been hard hit: in the Western Australian wheatbelt, for example, Kitchener et al. (1980) and Burbidge and McKenzie (1989) concluded that, from a total mammal fauna of 56 species (32 marsupials), 14, including nine marsupials, were locally extinct and 12, including 11 marsupials, were threatened with extinction. Some of the latter species are now recovering in remnant vegetation following fox control.
The marsupial faunas of the wet tropics are largely intact. Rainforests, which are of extremely limited extent in Australia, are of great importance to the conservation of a number of relict and endemic marsupial species, e.g. Atherton Antechinus (Antechinus godmani), Bennett's and Lumholtz's Tree-kangaroos (Dendrolagus bennettianus and D. lumholtzi), Green Ringtail Possum (Pseudochirops archeri), Daintree River and Herbert River Ringtail Possums (Pseudochirulus cinereus and P. herbertensis), Long-tailed Pygmy-possum (Cercartetus caudatus) and Musky Rat-kangaroo (Hypsiprymnodon moschatus).
The marsupial faunas of the moist temperate zones have suffered declines intermediate between those of the wet tropics and semi-arid lands. In the wetter temperate areas of the south-east and south-west the effects of introduced herbivores and fire have not been as marked as in arid or semi-arid lands. The loss of the Eastern Quoll and small macropods and potoroids and the decline of bandicoots in the south-east is most likely due to the combination of habitat change brought about by agriculture and exotic predators, possibly exacerbated by disease. In the south-west, CWR species have also declined considerably because of habitat change, but their decline has been buffered by the presence of vegetation containing natural fluoro-acetates, a powerful toxin, to which the local indigenous populations have evolved considerable tolerance, not shared by exotic predators. Several marsupials that are extinct in most of their mainland range have survived as relict populations in this area, e.g. Chuditch (Dasyurus geoffroii), Numbat (Myrmecobius fasciatus), Woylie (Bettongia penicillata), and Tammar Wallaby (Macropus eugenii).