The Brush-tailed Rock-wallaby Petrogale penicillata was once abundant in NSW and Victoria. Between 1880 and 1914 thousands were killed as vermin and for their beautiful skins. They may never have been abundant in the Warrumbungle Mountains. In the 1920s and 1930s only small isolated colonies existed and they were considered a novelty by landowners.

Over the last two centuries the environment of the Warrumbungles has been altered. Sleeper cutters removed many large trees and many more trees were ring-barked to encourage grass growth. Sheep and rabbits made sure that the understorey was kept open. In recent decades some parts of the bush has responded to less canopy, less sheep and less rabbits by thick regrowth of young trees and shrubs. It is not known how these changes have affected the Rock-wallaby population.

The Warrumbungle population of Brush-tailed Rock-wallabies was considered extinct by 1991. Then, from 1993 extensive survey work by NPWS officers located 7 small colonies in remote rocky areas on the northern and western side of the National Park. (in some cases in the same locations as remembered by 90yo Ted Morrissey from his youth). There is some concern that some of these colonies are no longer active (as indicated by scats) and the rock-wallabies may have died out or moved. It is not known how much the Brush-tailed Rock-wallabies move around and there is concern about the level of interchange between colonies as they appear to be isolated from each other.

Genetic studies have indicated that the Brush-tailed Rock-wallabies from the Warrumbungles are most closely related to other populations inland from the Central Coast of NSW