Brush-tailed rock-wallaby (Petrogale penicillata) - endangered species listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Brush-tailed Rock-wallaby Petrogale penicillata (Gray, 1825) as an ENDANGERED SPECIES in Part 1 of Schedule 1 of the Act, and as a consequence, omit reference to the Brush-tailed Rock-wallaby, Petrogale penicillata (Gray, 1852) Warrumbungles population from Part 2 of Schedule 1 (Endangered Populations) of the Act, and also omit reference to the Brush-tailed Rock-wallaby, Petrogale penicillata (Gray, 1825) from Schedule 2 (Vulnerable Species) of the Act. Listing of endangered species is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Brush-tailed Rock-wallaby Petrogale penicillata is a highly agile and distinctively marked medium-sized wallaby, which occupies rocky habitats.

2. The Brush-tailed Rock-wallaby was once abundant and ubiquitous throughout the mountainous country of south-eastern Australia (Short and Milkovits 1990). Their distribution roughly followed the Great Dividing Range for 2 500 km from the Grampians in western Victoria to Nanango in south-east Queensland, with outlying populations in the coastal valleys and ranges to the east of the Divide, and the slopes and plains as far west as Cobar in NSW and Injune (500 km NW of Brisbane) in Queensland (Short and Milkovits 1990).

3. The Brush-tailed Rock-wallaby has declined significantly in the west and south of its former range, and populations have become more fragmented throughout. Most populations are now small and isolated. The species has become increasingly restricted to isolated cliffs scattered throughout parts of its former range. Habitats occupied by this species tend to take one of three forms: loose piles of large boulders containing a maze of subterranean holes and passageways; cliffs (usually over 15m high) with many mid-level ledges and with some caves and/or ledges covered by overhangs; and isolated rock stacks, usually sheer-sided and often girdled with fallen boulders (Short 1982). These habitats are likely to be a subset of those occupied by the species prior to European settlement, and may represent refuge sites in which competition and predation pressures are reduced. Vegetation forms a vital habitat component (especially in refuge sites in association with rock outcrops), but its importance has been largely overlooked in many areas. It appears to be a vital shelter and food resource (Paul Bayne, pers. comm.).

4. Three genetically distinctive groups of Brush-tailed Rock-wallabies have been identified on the basis of mitochondrial DNA analyses. Due to a lack of taxonomic resolution, these groups are referred to as Evolutionary Significant Units (ESUs):

1. Central ESU: a well-defined group consisting of closely related populations in the region from central NSW, including Kangaroo Valley, Jenolan Caves, Broke and the Warrumbungles;
2. Northern ESU: a less well-defined group comprising locations in north-east NSW and south-east Queensland, which extends as far south as Armidale. At the northern end, there exists a narrow hybrid zone between P. penicillata and  P. herberti);
3. Southern ESU: a highly divergent lineage from Victoria, and previously south-east NSW (NSW NPWS 2002).

5. The exact boundaries between the ESUs are yet to be determined. Interpretation of results obtained to date is that the three ESUs are likely to reflect historical population patterns, with each deriving from a single (possibly refuge) population. Up until quite recently (~100 years ago) it is likely that there was a low level of gene flow across all populations within each ESU, predominantly due to infrequent movement of individual males, with little movement of females (Mark Eldridge pers. comm.). This pattern is reflected in the results from preliminary microsatellite analyses, which indicate that each individual population also differs slightly from each other population.

6. Brush-tailed Rock-wallabies typically exhibit low migration rates between colonies and low recolonisation rates, further impeding persistence and recovery of colonies affected by threatening processes. Recent human induced changes have almost certainly disrupted the natural process of low level gene flow. As colonies are isolated and restricted, migration is likely to be impeded, and the long-term future of any population that is now completely isolated is questionable.

7. The initial decline of the Brush-tailed Rock-wallaby can be attributed to three factors: hunting for bounty and fur, predation by introduced predators (e.g. foxes and dogs), and competition with introduced herbivores (e.g. feral goats, rabbits and stock). Patterns of decline reflected historical land use and hence climatic, soil and vegetative patterns, in combination with the persistence of the dingo (which kept goats and foxes in check). Ongoing predation and competition continue to threaten this species, as does habitat modification by fire, floods invasion by exotic weeds and clearing. Drought, inbreeding, human disturbance, illegal shooting, road kills, disease transmission by feral carnivores (toxoplasmosis and hydatidosis), and synergistic effects, such as interactions between habitat fragmentation and fox predation, also threatened populations of the Brush-tailed Rock-wallaby.

8. Brush-tailed Rock-wallabies differ in status between the three ESUs. All populations within the Southern ESU are believed to be extinct in NSW. In contrast, few populations within the Northern ESU are known to have declined to extinction. The persistence of extensive high quality habitat, large populations comprising many colonies with good gene flow, and reduced predation pressure typify this region. Within NSW, Brush-tailed Rock-wallaby distribution and population declines have occurred principally in southern and western areas. The Central ESU contains one population that is currently listed, many populations in decline and an increasing number of extinct populations.

9. In view of the above the Scientific Committee is of the opinion that Brush-tailed Rock-wallaby Petrogale penicillata (Gray, 1825) is likely to become extinct in nature in New South Wales unless the circumstances and factors threatening its survival or evolutionary development cease to operate.

Associate Professor Paul Adam
Chairperson
Scientific Committee

Proposed Gazettal date: 4/07/03
Exhibition period: 4/07/03 - 15/8/03

References

NSW NPWS. 2002. Brush-tailed Rock-wallaby (Petrogale penicillata) Recovery Plan. Draft for public comment. Hurstville.

Short, J. 1982. Habitat requirements of the Brush-tailed Rock-wallaby,Petrogale penicillata, in NSW.  Australian Wildlife Research. 9: 239 - 46.

Short, J. and Milkovits, G. 1990. Distribution and status of the Brush-tailed Rock-wallaby in south-eastern Australia. Australian Wildlife Research.17: 169 -79.