General information

Kangaroos are marsupials and belong to the Family Macropodidae (i.e. big feet) that is grouped with the Potoroidae (potoroos, bettongs, rat-kangaroos) and Hypsiprymnodontidae (musky rat-kangaroo) in the Super-Family, Macropodoidea. This comprises around 50 species in Australia and a dozen or more in New Guinea.  Some of the smaller species, such as Yellow-footed Rock-Wallabies, Burrowing Bettongs, accompanied Pig-footed and Golden Bandicoots, Bilbies and possibly Hairy-nosed Wombats into extinction with the advent of pastoralism. However, the largest species remain in much of their original range with the grey kangaroos expanding inland as grazing habitat increased and coastal habitat was lost in clearance for agriculture. The defining feature of the kangaroo family is that they are the largest vertebrates to hop (both currently and from what we know from palaeontology).

 

The Rock-wallabies (Petrogale spp.) is the most diverse genus amongst the living macropods with 16 species ranging from 1 to 12 kg in size. They are found across mainland Australia and on some recently separated offshore islands but not on the Bass Strait Islands, Tasmania or New Guinea. The species diversified from a common ancestor about 4 million years ago and their closest affinity to other macropods is with the Tree-kangaroos. Diversification of species occurred in two waves. The first gave rise to the Short-eared Rock-wallaby, the Monjon, the Narbelek, the Yellow-footed Rock-Wallaby and the Proserpine Rock-wallaby. The second was about a million years ago and lead to species that are not all morphologically distinctive like those along the Queensland seaboard. All Rock-wallabies favour habitat with rocky outcrops and slopes, cliffs and gorges or are found on boulder piles and escarpments especially in the wet-dry tropics. Their ability to scale precipitous rock faces in leaps that appear to defy gravity comes from adaptations to the feet and tail. The feet are short relative to the majority of macropods that inhabit flat ground. The pads are thick, spongy and highly granulated so that they compress on the rock surface and maximise grip. The tail is long and cylindrical with little taper and great flexibility. The tail acts as a counterbalance and rudder in rapid hopping across uneven surfaces and allows changes of direction in mid-air.

Species

Brush-tailed Rock-wallaby

Petrogale penicillata ('brush rock-weasel')

Best place to see

Oxley Wild Rivers National Park, New South Wales

The Oxley Wild Rivers National Park is a major refuge for the once widespread Brush-tailed Rock-wallaby. The Parkcontains the largest remaining population of about 10,000 individuals. There has been a massive reduction in this Rock-wallaby's range as the southern NSW and Victorian populations have largely become extinct.  The Park is dispersed between several major towns - Armidale, Walcha and Dorrigo - in the New England area of NSW. Some of the gorges close to Armidale are likely sites to see the Brush-tailed Rock-wallaby. For example, Gara Gorge is 18 km south-east of Armidale along the Castledoyle Road. Dangars Gorge and Falls are 22 km south-east of Armidale along the Dangersleigh Road.  Dangars Gorge has 10 camp sites with drinking water, pit/composting toilets, picnic tables, electric/gas barbecues, wood barbecues.

The Park has a number of other macropod species including Eastern Grey Kangaroos, Common Wallaroos, Red-necked Wallabies, Red-necked Pademelons and small population of Parma Wallabies.

Identification

Males  to 10.9 kg (average 7.9 kg) and females to 8.2 kg (average 6.3 kg).  The Brush-tailed Rock-wallaby has long, dense fur with a coarse texture.  The general dorsal colour from mid back to rump is grey-brown. The rump is rufous brown. Individual hairs have dark grey bases with a brown mid-band, with either a pale or black tip on the back, and a paler tip on the rump.  The fur is longer towards the rump.  From the face to between the ears is dark grey-brown and from the crown to the shoulder area the fur is a paler grey-brown.  The nose is naked and black.  There is an indistinct broad dark stripe from the nose through the eye to the base of the ear.  The dark stripe is offset below by a broad white to pale buff stripe.  A narrow black dorsal stripe begins between the eyes and reaches to the back of the head.  The upper sides of the ears have a pale grey base and black tip. The posterior edge of the ear is yellow and the sparse hair inside the ear if a buff yellow.  The shoulders are marked by is a large black patch that may extend some distance down the side, bounded by a pale-grey stripe that extends down the side.  The arms and legs are grey-brown and the feet are dark brown to black.  The hands, fingers and the toes are black.  The base of the tail is yellow-brown with a paler underside.  The remainder of the tail is black and the length of the hair increases towards the tip, so that the tail terminates with a prominent brush.  Some individuals have a few white or pale-yellow hairs towards the tail tip.  The throat and upper chest are slate-grey and the abdomen is pale yellow-brown.  Many individuals have a central white throat patch, which is very small or extends in a blotchy manner to the chest.  Occasionally there may be small white patches on the base of the inner thigh. The Herbert’s and Brush-tailed Rock-wallabies are indistinguishable in the zone where they come together and hybridise. 

Habitat

The Brush-tailed Rock-wallaby has been distributed through rocky habitats embedded within a broad range of vegetation types indicative of the wide latitudinal range of its distribution. Vegetation types include temperate and sub-tropical rainforest, wet and dry sclerophyll forest, and open woodland. Within these habitats it shelters on ledges and in crevices and caves. This once abundant species is now extinct over most of its southern range. At the end of the 19th and into the early 20th Century it was classed as an agricultural pest and hunted for its skins. Around 500, 000 skins were officially traded. Predation by foxes is currently blamed for declining or extinguished populations but clearly unsustainable killing and habitat transformation for pastoral and agricultural enterprises set the course of most local extinction.

Foraging behaviour

Brush-tailed Rock-wallabies have the typical broad diet of their genus that includes short green grasses and herbs (forbs), along with significant browse (including a capability to hop into trees), and fruit, flowers and seeds when available and acessible. Native figs often grow out of rock faces and provide a fruit source in competition with possums, fruit-bats and frugivorous birds. Home ranges have been estimated from 2-30 ha and this variability likely reflects the quality of resources within the range and the flexibility to expand out from rocky habitat in times of paucity (e.g. drought). Brush-tailed Rock-wallabies rarely venture out of shelter during the day and are most likely seen late in the afternoon when they emerge to forage through the night. Inclement weather contraints foraging behaviour and they seek shelter from cold winds and rain.

Reproductive behaviour

Breeding occurs throughout the year but births may be concentrated in late summer and autumn so that young permanently leave the pouch in spring and early summer when rainfall peaks in temperature latitudes and grass germination and growth is highest. Polygamous mating occurs but there is some evidence of single males defending clusters of females.

Social organisation

Rock-wallabies are typically social and live in colonies varying from a few individuals to over 100. In the  Brush-tailed Rock-wallaby, females are philopatric (stay in natal home range) and so matrilines build up. Males disperse but do not necessarily leave the colony. Rocky day-time shelters are defended and used repetitively. Foraging ranges may overlap other individuals. The home range of males is typically larger than that of females.

Further readings

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

Eldridge MDB, Close RL (1997) Chromosomes and evolution in rock-wallabies, Petrogale (Marsupialia: Macropodidae). Australian Mammalogy 19, 123-135.

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

Eldridge MDB, Rummery C, Bray C, Zenger KR, Browning TL, Close RL (2004) Genetic analysis of a population crash in brush-tailed rock-wallabies (Petrogale penicillata) from Jenolan Caves, south-eastern Australia. Wildlife Research 31, 229-240.

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

Laws RJ, Goldizen AW (2003) Nocturnal home ranges and social interactions of the brush-tailed rock-wallaby Petrogale penicillata at Hurdle 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.

Wynd NM, Sigg DP, Pople AR, Hazlitt SL, Goldizen AW (2006) Factors affecting female reproductive success and the survival of pouch young in the threatened brush-tailed rock-wallaby, Petrogale penicillata. Australian Journal Of Zoology 54, 61-70.