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Petrogale penicillatabrush-tailed rock wallaby

By Kathleen Bachynski

Geographic Range

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; Taggart, 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; Taggart, et al., 2005)

Habitat

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)

  • Other Habitat Features
  • caves

Physical Description

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)

  • Sexual Dimorphism
  • male larger
  • Range mass
    4.0 to 10.9 kg
    8.81 to 24.01 lb
  • Range length
    45 to 58.6 cm
    17.72 to 23.07 in

Reproduction

Brush-tailed rock-wallabies breed year round. The few matings that have been observed among Petrogale penicillata involve only females and males who are established on refuges. A notable feature of brush-tailed rock-wallabies, as well as other Petrogale species, is close and regular association between the refuge-guarding male and the females who use his refuge. Association involves mutual grooming and unusually high tolerance of proximity. (Jarman and Bayne, 1997)

Though details are unavailable on brush-tailed rock-wallabies, most species of Macropodidae are promiscuous. Brush-tailed rock-wallabies have a different mating system than most related species in three respects: 1) a higher proportion of adult males are likely to take part in breeding and may do so for many years, 2) variance in male reproductive success is relatively low, and 3) only some weaned females, those able to establish themselves on a refuge, are likely to breed at all. (Jarman and Bayne, 1997)

Females are sexually mature by 18 months, and males by 20 months. They breed all year, mating soon after giving birth. Development of the embryo is delayed until the pouch is vacated. Pregnancy lasts 31 days, after which a single young is born and attaches to one of the 4 teats in the pouch. The young remains in the pouch for about 29 weeks, then suckles at foot for about three months. In captive animals, post-partum estrous was typically observed on the same day as birth, even sometimes appearing within a few hours. (Cronin, 2000; Johnson, 1979)

The process of birth has been observed on one occasion in the rock-wallaby Petrogale penicillata inornata. The female sat on the base of her tail, her body leaning forward in order to bring the head close to the urogenital opening and pouch. Birth was accompanied by a small amount of clear fluid and blood, which the mother cleaned as the newborn young went toward the pouch opening. It took 45 seconds for the infant to reach the pouch opening from the urogenital opening. The mother remained in the birth position for 10 more minutes, licking around the urogenital opening. (Johnson, 1979)

  • Breeding interval
    The breeding interval is unknown, but females can enter estrous shortly after giving birth and breed throughout the year.
  • Breeding season
    Brush-tailed rock-wallabies breed throughout the year.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    31 days
  • Average gestation period
    30 days
    AnAge
  • Average weaning age
    7 months
  • Average time to independence
    7 months
  • Average age at sexual or reproductive maturity (female)
    18 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    540 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    20 months
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    590 days
    AnAge

There are few details about parental investment in Petrogale penicillata. Young remain in the mother's pouch for around 29 weeks, where they receive protection and milk. After leaving the pouch, the evicted young continue to suckle for about 3 months. (Cronin, 2000)

  • Parental Investment
  • altricial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

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

Behavior

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)

  • Range territory size
    6 to 30 cm^2
  • Average territory size
    15 cm^2

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)

Communication and Perception

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, et al., 1997; Jarman and Bayne, 1997)

Food Habits

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)

  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit

Predation

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)

Ecosystem Roles

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)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

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)

  • Negative Impacts
  • crop pest

Conservation Status

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, et al., 1997; Dovey, et al., 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, et al., 1997; Dovey, et al., 1997)

Other Comments

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)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Kathleen Bachynski (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

embryonic diapause

At about the time a female gives birth (e.g. in most kangaroo species), she also becomes receptive and mates. Embryos produced at this mating develop only as far as a hollow ball of cells (the blastocyst) and then become quiescent, entering a state of suspended animation or embryonic diapause. The hormonal signal (prolactin) which blocks further development of the blastocyst is produced in response to the sucking stimulus from the young in the pouch. When sucking decreases as the young begins to eat other food and to leave the pouch, or if the young is lost from the pouch, the quiescent blastocyst resumes development, the embryo is born, and the cycle begins again. (Macdonald 1984)

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Bulinski, J., D. Goldney, J. Bauer. 1997. The habitat utilisation and social behaviour of captive rock-wallabies: implications for management. Australian Mammalogy, 19: 191-198.

Carter, K., A. Goldizen. 2003. Habitat choice and vigilance behavior of brush-tailed rock-wallabies (Petrogale penicillata) within their noctural foraging ranges. Wildlife Research, 30: 355-364.

Cronin, L. 2000. Australian Mammals. Annadale, NSW: Envirobook.

Dovey, L., V. Wong, P. Bayne. 1997. An overview of the status and management of rock-wallabies (Petrogale) in New South Wales.. Australian Mammalogy, 19: 163-168.

Eldridge, M., R. Close. 1995. Brush-tailed rock-wallaby. Pp. 383-385 in R Strahan, ed. The Mammals of Australia. Chatswood, NSW: Reed Books.

Jarman, P., P. Bayne. 1997. Behavioural ecology of Petrogale penicillata in relation to conservation. Australian Mammalogy, 19: 219-228.

Johnson, P. 1979. Reproduction in the plain rock-wallaby, Petrogale penicillata inornata Gould, in captivity, with age estimation of the pouch young. Australian Wildlife Research, 6: 1-4.

Lavery, H., T. Kirkpatrick. 1985. Kangeroos as pests. Pp. 103-132 in H Lavery, ed. The Kangeroo Keepers. St. Lucia, Queensland: University of Queensland Press.

Laws, R., A. Goldizen. 2003. Noctural home ranges and social interactions of the brush-tailed rock-wallaby Petrogale penicillata at Hurlde Creek, Queensland. Australian Mammalogy, 25: 169-176.

Short, J. 1989. The diet of the brush-tailed rock-wallaby in New South Wales. Australian Wildlife Research, 16: 11-18.

Short, J., G. Milkovits. 1990. Distribution and status of the brush-tailed rock-wallaby in south-eastern Australia. Australian Mammalogy, 17: 169-179.

Taggart, D., D. Schultz, C. White, P. Whitehead, G. Underwood, K. Phillips. 2005. Cross-fostering, growth, and reproductive studies in the brush-tailed rock-wallaby, Petrogale penicillata (Marsupialia: Macropodidae): efforts to accelerate breeding in a threatened marsupial species. Australian Journal of Zoology, 53: 313-323.

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