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

Black-footed Rock-wallaby (Recherche Archipelago)

Petrogale lateralis hacketti ('Hackett's notable-sided rock-weasel')

Best place to see

Recherche Archipelago, Western Australia

The Recherche Archipelago is a group of 105 islands of the southern coast of Western Australia out from the port of Esperance. Woody Island is a nature reserve accessible by ferry and has some accommodation. The Black-footed Rock-wallabies are found on Mondrain (820 ha), Wilson (90 ha) and Westall (70 ha) Islands. Interestingly, the mainland and nominate subspecies Petrogale lateralis lateralis is found on Salisbury Island (320 ha) which is also part of the Recherche Archipelago.

Identification

Males and females to 5.3 kg (average 5.0 kg). The Recherche Archipelago Black-footed Rock-wallaby is similar in appearance to the mainland Western Australian subspecies but is a little larger on average. The Black footed Rock-wallabies have a long and soft fur and is woolly around the rump.  The back is coloured grey with a red-brown tinge over most of the back.  The colouration is lighter and browner in the summer coat. The shoulders are silver-grey changing to dark grey on the top ahead, with black tips to the individual hairs.  The face is a dark grey and has a well-defined dark stripe from the front of the upper lip through the eye to the base of the ear, highlighted below by a white stripe from the lower lip, passing below the eye to below the ear.  A narrow dark brown to black dorsal stripe runs from between the ears to the centre of the back.  The outer ear is yellow at the base with the remainder brown except for yellow at the very tip.  The inner ear is sparsely haired.  A prominent broad brown to black stripe starts behind the elbow and extends down the side to the inside of the thigh.  This is defined above by a narrower white stripe from the shoulders to the hip.  The arms, legs and feet are grey, like the back, and the fur on the fingers and toes is black.  The fur on the inside of the arms is brown.  The first half or more of the tail is grey, like back, and terminates in a modest black brush.  The underside of the chin, body and tail is yellow-grey.

Habitat

The Recherche Archipelago subspecies occupies granite outcrops and rock crevices that extend down to the sea. The principle substrate is migmatite which is deeply cracked. The islands differ in size and thus diversity of habitats. Mondrain Island is covered by low Eucalypt woodland with a thick scrubby understorey. There is some heath on sandy soil overlying outcropping rock. Westall Island is treeless and covered by a chenopod shrubland of saltbushes (Atriplex spp.), spiny saltbushes (Rhagodia spp.) and Ruby Saltbush (Echylaena tormentosa). Fresh water seepages occur along the shoreline and support grasses like Sporobolus virginicus, sea-heaths like Frankenia tetrapetala and low forbs like Lobelia anceps that are grazed by the Rock-wallabies. Wilson Island is mainly low heath.

Foraging behaviour

The diet of the Recherche Archipelago subspecies comprises mainly succulents, forbs and grasses.

Reproductive behaviour

Reproduction has been studied in a sample of Black-footed Rock-wallabies held in captivity. The  characteristics are an oestrus cycle of 30 d, post-partum oestrus, embryonic diapause, a pouch life of 6-7 months, with weaning at 11 months. Breeding is continuous but tends to a spring peak in southern populations like those in the Recherche Archipelago.

Social organisation

Rock-wallabies are typically social and live in colonies varying from a few individuals to over 100. In the closely related 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.

Further readings

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

Eldridge MDB, King JM, Loupis AK, Spencer PBS, Taylor AC, Pope LC, Hall GP (1999) Unprecedented low levels of genetic variation and inbreeding depression in an island population of the Black-footed Rock-wallaby. Conservation Biology 13, 531-541.

Eldridge MDB, Kinnear JE, Onus ML (2001) Source population of dispersing rock-wallabies (Petrogale lateralis) identified by assignment tests on multilocus genotypic data. Molecular Ecology 10, 2867-2876.

Pearson DJ, Kinnear JE (1997) A review of the distribution, status and conservation of rock-wallabies in Western Australia. Australian Mammalogy 19, 137-152.