National Recovery Plan for the Brush-tailed Rock-wallaby

Habitat

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  Loose piles of large boulders containing a maze of subterranean holes and passageways.
  
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  Cliffs with many mid-level ledges and with some caves and/or ledges covered by overhangs.
  
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  Isolated rock stacks, usually sheer-sided and often girdled with fallen boulders.
  

Prior to European settlement, the Brush-tailed Rock-wallaby may have also occurred in non-rocky forests and woodlands, especially those on steep slopes and with cover in the form of dense vegetation and large fallen logs or trees (Jarman & Bayne 1997). The apparent restriction of Brush-tailed Rock-wallabies to rocky habitats may be relatively recent, and is probably a consequence of threatening processes operating on the species.

Important Populations

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  Grampians Range – a reintroduced population (East Gippsland provenance) comprising 11 animals at Moora Moora Creek (Grampians National Park).
  
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  East Gippsland – about 20 wild and two released captive-bred animals (East Gippland provenance)in Little River Gorge area, south-east of Wulgulmerang (Snowy River National Park).
  

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  Warrumbungle Range (outlying population; loss would cause substantial range contraction).
  
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  Mt Kaputar (outlying population; loss would cause range contraction).
  
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  Wollemi National Park and Jenolan Caves [stronghold populations where fox control may be most effective (due to distance from agricultural land) and so populations have the greatest chance of persisting into the long term].
  
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  Nattai National Park population (loss would create a large range gap between the Shoalhaven population and populations further north).
  
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  Shoalhaven (southernmost population in NSW).
  
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  Macleay Gorges region (largest known populations).
  

Decline and Threats

In Victoria (S-ESU), the Brush-tailed Rock-wallaby occurred in the Grampians in the west of the State, and in Gippsland in the east, from Mt Kent to near Deddick (Menkhorst 1995) and probably was contiguous with populations in southern New South Wales. The species was once widespread in the Grampians (Close et al. 1988), but by 1986 only four colonies remained (Norris & Belcher 1986). This decline continued until extinction; with the last known wild animal captured and taken into captivity in 1999. The species disappeared from almost all of its former distribution in Gippsland, and now survives in a few isolated colonies in the upper Snowy River area comprising perhaps 20 animals (Waldegrave-Knight & Stevens 2003).

In New South Wales, the species once occurred from the Victorian border north to the Queensland border (including the ACT) and west as far as Bourke and Mt Hope. The species is no longer found south of Nowra/Goulburn, including the ACT (where it was last recorded in 1959; EACT 1999); and from virtually all sites west of the GDR, including Coombie, Gundabooka, Mt Oxley and the Weddin Mountains (Short & Milkovits 1990; Dovey et al. 1997; DECC 2008). In this region small populations still occur in the Warrumbungle Range near Coonabarabran, and on Mt Kaputar. Remaining colonies are now almost entirely scattered along the GDR, from the few small, isolated colonies in the Shoalhaven area in the south to the numerous colonies close to the Queensland border. The species has generally disappeared from the GDR tablelands, but remains relatively common in the valleys and gorges of the eastern scarp of the GDR in north-east NSW. Many colonies still occur between that scarp and the coast.

Little is known of the extent of the decline in Queensland. A survey in the late 1990s found evidence of Brush-tailed Rock-wallaby presence at 131 sites (Capararo 1998). Half of these sites (65) were primarily on private land and 48 (74%) of these were occupied by rock-wallabies at the time of the survey. Fifty-four sites (41%) occurred in conservation reserves and 46 (85%) of these were occupied. None of the 12 (9%) sites in State Forest were shown to be occupied. The species is now apparently extinct on the western scarp of the GDR in the Stanthorpe district (Murray 2009).

The naturally fragmented nature of refuge habitat results in many distinct, separated colonies that are effectively isolated from one another. Many colonies consist of just a few animals and, even in the parts of their range where the species remains locally common, many colonies (perhaps most) number less than 12 adults ( Jarman and Bayne 1997). While colonies as small as 2–4 adults can persist for some years, at this size they are very prone to demographic stochasticity and probably ultimately become extinct. However, in the Central and Northern ESU, some colonies contain 30–50 adults (Piggot et al. 2006b; P. Bayne unpubl. data 1994; A. Goldizen unpubl. data 2005).

The principal threats to the Brush-tailed Rock-wallaby are not well understood, and further investigation is required to clarify which of the likely threatening processes are the key ones. While some declines happened decades ago, the decline is continuing in some areas, as evidenced by the ongoing loss of individual colonies. Remaining populations are generally highly fragmented and isolated from one another. The disjunct nature of its distribution makes populations particularly susceptible to local extinction from stochastic events such as fire, drought and disease. However, the direct causes of any colony’s extinction have never been established. There are several historic and current threats that have undoubtedly contributed to the decline of the Brush-tailed Rock-wallaby, as summarised in the following sections:

The initial decline of the Brush-tailed Rock-wallaby, especially from locations in the south and west of its range, may well have been caused by large numbers of animals being killed for fur and meat, and as a supposed agricultural pest. Over half a million rock-wallabies were killed in NSW between 1884 and 1914 (Eldridge & Close 1995), while in East Gippsland (Vic), over 1,200 animals were killed during one winter alone near Suggan Buggan (Rogers, cited in Menkhorst 1995). By the time this persecution ceased, the species was already rare in the west and south of its range.

Degradation of the Brush-tailed Rock-Wallaby’s habitat has been caused by a number of factors. Since European settlement, the effective isolation of many colonies has probably increased because the habitat between colonies has been degraded through vegetation clearance, livestock grazing and timber harvesting. This has probably reduced the frequency of successful dispersal between colonies and thus increased the isolation of colonies and populations (Jarman & Bayne 1997), leaving them even more vulnerable to inbreeding and loss of genetic diversity. Habitat modification continues due to rural residential and tourist developments adjacent to some colonies (especially in northern NSW), and the current trend of locating these developments near escarpments and cliff lines to maximise scenic opportunities. Such sites are often core Brush-tailed Rock-wallaby habitat and development increases the risk of colony fragmentation, permanent changes to potential dispersal corridors, an increase in the numbers of domestic animals and the removal of tree cover. The impacts of wildfires and managed fires on the animals and their habitat (especially food supply) are not known. Temporary abandonment of a colony site at Mount Wallerawang after a fire, and subsequent recolonisation several years later, has been anecdotally reported (DECC 2008).

The Brush-tailed Rock-wallaby faces a range of both native and introduced predators, including the Dingo/wild Dog (Canis lupus), Red Fox (Vulpes vulpes), feral Cat (Felis catus), Wedge-tailed Eagle (Aquila audax), Spotted-tailed Quoll (Dasyurus maculatus) and Carpet/Diamond Python (Morelia spilota) (Bayne 1994; Menkhorst 1995; Jarman & Bayne 1997). Predation by introduced predators, especially the Red Fox and possibly feral Cat, poses a significant threat to small mammals (Risbey et al. 2000), including the Brush-tailed Rock-wallaby (Hill 1991; EACT 1999; Waldegrave-Knight & Stevens 2003; DECC 2008). Because of their reliance on particular secure refuges, Brush-tailed Rock-wallabies are susceptible to predators that can learn the location of refuges, and movement pathways to and from them (Jarman & Bayne 1997). A single feral Cat on an isolated population of the Allied Rock-wallaby Petrogale assimilis (weight to 4.5 kg), killed five (45.5%) of the young, one (14.2%) of the sub-adults and at least two (4.6%) of the adult population (Spencer 1991). The current restriction of rock-wallabies to rocky habitat is possibly relatively recent, and may well be an artefact of fox predation (as well as habitat destruction), with foxes able to prey more easily on rock-wallabies in structurally less complex habitat. In forest areas in eastern NSW, proximity to cleared freehold land or intensive logging was associated with increased abundance of the Red Fox (Catling & Burt 1995). Therefore, distance to cleared land, or highly disturbed land, including vehicle tracks and logging coupes, may be an important variable in determining the persistence of Brush-tailed Rock-wallaby colonies.

Other native and introduced herbivores may compete with Brush-tailed Rock-wallabies for food and shelter. Rock-wallabies frequently share their foraging habitat with European Rabbit (Oryctolagus cuniculus), feral Goat (Capra hircus), feral Horse (Equus caballus), Eastern Wallaroo (Macropus robustus), Eastern Grey Kangaroo (Macropus giganteus), Whiptail Wallaby (Macropus parryi), Red-necked Wallaby (Macropus rufogriseus), Black Wallaby (Wallabia bicolor), Mountain Brushtail Possum (Trichosurus cunninghami) and Common Brushtail Possum (Trichosurus vulpecula). If competing species reach high densities they could pose a threat to the Brush-tailed Rock-wallaby, through reduced food supply, reduced condition, breeding success and survival. Goats have been observed to displace rock-wallabies from their refuge areas, and monitoring in Warrumbungle Range demonstrated a negative correlation between the density of goat pellets and rock-wallaby pellets in both foraging and refuge areas (Moss et al. 1997). Goats were also speculated to have been the cause of the extirpation of the Dingo Creek colony in Warrumbungle National Park (Moss et al. 1999). Short and Milkovits (1990) suggested that goats have had more of a detrimental impact on Brush-tailed Rock-wallabies west of the Great Dividing Range than in the coastal ranges.

In most parts of its range the Brush-tailed Rock-wallaby probably always occurred as a metapopulation comprised of colonies centred on areas of high-quality rock habitat that provided adequate refuges within reach of reliable food resources. Although adults show high fidelity to refuge sites, sub-adults (mostly males) did move between colonies, which probably overcame genetic problems associated with isolation of small populations. However, since European settlement of eastern Australia, the isolation of many colonies has probably increased because the habitat between colonies has been degraded and as a consequence of a high level of predation. When this isolation is coupled with decreased population size, as is the case with the Victorian and many NSW populations, the rate of loss of genetic diversity due to founder effects and genetic drift is greatly increased, and this variation is not readily replenished in isolated populations. Small isolated populations are also often subject to increased rates of inbreeding (Charlesworth & Charlesworth 1987). The loss of genetic variation in a population reduces the ability of the population to respond to environmental change and increases the risk of extinction, through increased inbreeding and genetic drift causing increased homozygosity (Charlesworth & Charlesworth 1987). Increased homozygosity can have negative effects on individual fitness both because there is an intrinsic advantage to heterozygosity for some genes and gene complexes (Ferreira & Amos 2006) and it can lead to an increase in the frequency of expression of recessive deleterious alleles (Charlesworth & Charlesworth 1987).

Areas occupied by Brush-tailed Rock-wallabies that are under threat have not been precisely defined. However, sites on private land (about 40% of current or recently occupied sites are on private land: DECC 2008) are probably more at risk than those in parks and reserves (although the generally rugged nature of rocky habitat reduces options for land use). The expansion of rural residential and tourist developments adjacent to some colonies, especially in northern NSW, and the current trend of locating these developments near escarpments and cliff lines to maximise landscape views, is probably a threat. Such sites are often core Brush-tailed Rock-wallaby habitat and development increases the risk of colony fragmentation, permanent changes to potential dispersal corridors, an increase in the numbers of domestic animals and predators, and the removal of tree cover.

There is some information to enable identification of populations under threat. Both populations of the Southern ESU (Grampians reintroduced and East Gippsland), and most (if not all) remaining populations in the Central ESU are under threat and require active, ongoing management. Little is known of which Northern ESU populations are under threat.