Petrogale penicillata
brush-tailed rock wallaby

Native to Australia, brush-tailed rock-wallabies are distributed along rocky escarpments of the Great Dividing Range from southern Queensland to western Victoria. Although common in south-eastern Queensland and northern New South Wales, populations in the southern and western parts of the range have declined. Remnant populations in Victoria and western New South Wales are endangered. Only three colonies in south-eastern Australia remain, and estimates of the total wild population in this region are at fewer than 12 individuals. (Eldridge and Close, 1995; Phillips et al., 2005)

Petrogale penicillata was introduced to Hawaii and New Zealand. In Hawaii, a small population of rock-wallabies, descended from two animals, has existed on the island of Oahu since 1916. In New Zealand, brush-tailed rock-wallabies were introduced in the 1870s and can be found on Kawau, Rangitoto, and Montutapu islands. On some of these islands rock-wallabies are regularly culled because they have reached pest proportions. (Eldridge and Close, 1995; Phillips et al., 2005)

Brush-tailed rock-wallabies live on rock faces close to grassy areas and often in open forests. They prefer sites with numerous ledges, caves, and crevices. They typically occupy sites with a northerly aspect, in order to sun themselves in the morning and the evening. Originally widespread and abundant, brush-tailed rock-wallabies were found in suitable rocky areas in a wide variety of habitats, including rainforest gullies, wet and dry sclerophyll forest, open woodland, and rocky outcrops in semi-arid country. (Cronin, 2000; Eldridge and Close, 1995)

Petrogale penicillata has a dull-brown back, paler chest and belly, a rufous rump and black, furry feet. They have a black axillary patch often extending as a dark stripe to the margin of the hindlegs. Their tail darkens distally with a prominent brush. Their pelage is long and thick, especially about the rump, flanks and base of tail. Animals from the northern part of the range tend to be lighter and have a less prominent tail brush. They have long tails, slightly longer than their head and body length. Head and body length averages 55.7 cm in males and 53.6 cm in females, while tail length averages 61.1 cm in males and 56.3 cm in females. (Cronin, 2000; Eldridge and Close, 1995)

Captive brush-tailed rock-wallabies have lived over 11 years. (Lavery and Kirkpatrick, 1985)

Brush-tailed rock-wallabies are social animals that form small colonies with dominance hierarchies. Individuals have overlapping home ranges with exclusive den sites. Females are gregarious; they often share den sites with their female relatives and they regularly groom each other. Rock-wallabies maintain an attachment to a precisely defined habitat with a strict social organization. One observed population of brush-tailed rock-wallabies maintained, during both good and bad years, an adult population of five to seven individuals by violently evicting young soon after weaning. In captivity, this means that weaned young may be killed if they are unable to escape from the enclosure. Males are rarely within 5 meters of another male. When males are in close proximity, there is almost always a violent interaction. Females are more tolerant of the close proximity of other females than are males of other males. Females do, however, commonly displace one another and engage in agonistic interactions. Additionally, females have been seen driving away female and sub-adult male intruders from the vicinity of their refuges.

Due to the difficulties of nocturnal observations, much more remains to be learned about the behavior of brush-tailed rock-wallabies. (Carter and Goldizen, 2003; Cronin, 2000; Jarman and Bayne, 1997; Lavery and Kirkpatrick, 1985)

Home Range

Adult males have been found to have significantly larger nocturnal ranges than females, possibly due to their greater energetic requirements or in order to increase their mating opportunities. Range size is likely affected by the productivity and nutritional value of vegetation at different sites. High levels of home range overlap are probably due to patchy distributions of resources, which leads to aggregation at sources of shelter or food. (Laws and Goldizen, 2003)

Petrogale penicillata engages in allogrooming, where one animal bites and licks the fur of another animal, which may serve a role in reinforcing dominance status. Other examples of communicative behaviors include making vocalizations (a hissing cough sound), staring intensely, and aggressive behaviors such as nose jabbing (one animal thrusting its nose toward another animal). Males may examine potential female mates by approaching the female and sniffing her rump or cloaca.

Additionally, some evidence suggests that adult males deposit scent marks within their area of control. (Bulinski, Goldney, and Bauer, 1997; Jarman and Bayne, 1997)

Petrogale penicillata feeds largely on grasses, which comprise 35-50% of its total diet, but will supplement its diet with leaves, sedges, ferns, roots, bark, fruit, seeds and flowers. Brush-tailed rock-wallabies choose to forage in locations with more forbs and short green grasses. There is little seasonality of diet. Also, the relative proportions of different food types in the diet are vary little among regions, despite varying vegetation. This sugests definite food preference with little or no seasonal shortages of preferred foods. Since brush-tailed rock-wallabies eat a wide range of food items, they are likely buffered against drought and against competition with more specialized herbivores. (Carter and Goldizen, 2003; Cronin, 2000; Short, 1989)

Since brush-tailed rock-wallabies exhibit very high fidelity to diurnally used sites, predators may find it easy to learn where to find them. Furthermore, because colonies are small (due to declining population size), fewer individuals are available to be alert in order to detect and warn of approaching predators. Since Petrogale penicillata has been observed to maintain a relatively constant level of vigilance regardless of surrounding vegetation, however, it has been suggested that these animals rely on early detection of predators. Additionally, brush-tailed rock-wallabies are much more agile than their predators. (Carter and Goldizen, 2003; Jarman and Bayne, 1997)

When they were more widespread, brush-tailed rock-wallabies substantially affected agricultural plant species. In 1880, legislation was passed in New South Wales declaring kangaroos and wallabies as vermin. A bounty was offered on brush-tailed rock-wallabies, suggesting that they threatened agricultural production. They apparently invaded orchards and vegetable gardens with their ability to jump on top of fences, and fed heavily on the plants there. Additionally, it is possible that brush-tailed rock-wallabies help disperse the seeds of the fruit they eat. For instance, large numbers of the seeds of Persoonia linearis were found in the wallabies' faecal pellets collected in the spring. (Short and Milkovits, 1990; Short, 1989)

When brush-tailed rock-wallabies were more widespread in Australia, they were shot as agricultural pests. They were able to enter and feed in orchards, and vegetable gardens required fences several meters high to exclude them. (Short and Milkovits, 1990)

Captive populations of Petrogale penicillata are the focus of behavioral, management and genetic research. (Dovey, Wong, and Bayne, 1997)

In many parts of New South Wales, Petrogale penicillata populations have been reduced to small, isolated colonies. Predation, notably by red foxes (Vulpes vulpes), an introduced species to Australia, appears to be the current major threat to Petrogale penicillata. Habitat degradation through vegetation and fire changes, competition with goats, rabbits and sheep, and vulnerability to drought and disease may also be involved. Brush-tailed rock-wallabies have been observed to leave properties where sheep were introduced, suggesting that the habitat-specific rock-wallabies were starved out by the much more ubiquitous sheep. (Bulinski, Goldney, and Bauer, 1997; Dovey, Wong, and Bayne, 1997; Lavery and Kirkpatrick, 1985)

The observation of the dramatic decline of a wild colony at the Jenolan caves in central New South Wales led to the first concerted management response to the continuing decline of Petrogale penicillata. The colony was of unknown size but supplemented by the release of 88 locally enclosure-bred animals in 1988. Late in 1992, the remaining wild animals at Jenolan were trapped and transferred to a nearby enclosure with the goal of establishing a captive breeding program. Such captive breeding programs generally allow for a far greater degee of direct control than can be exercised with wild animals. The NSW National Parks and Wildlife service (NPWS) has responded to the ongoing decline of Petrogale penicillata by initiating a program incorporating: 1) A survey to locate all sites where Petrogale penicillata> is extant; 2) a community awareness and involvement campaign; 3) the development and implementation of Population Management Plans (PMPs) for extant sites; 4) on-going research into threats and impacts. (Bulinski, Goldney, and Bauer, 1997; Dovey, Wong, and Bayne, 1997)

An apparently narrow hybrid zone has formed between Petrogale penicillata and Petrogale herberti. In this zone, at the north of Petrogale penicillata's range, some female hybrids are fertile, which allows limited gene exchange between the two populations. This exchange is not widespread, however, allowing each species to retain its genetic identity. (Eldridge and Close, 1995)