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

Purple-necked Rock-wallaby

Petrogale purpureicollis (' purple-necked brush rock-weasel')

Best place to see

Boodjamulla (Lawn Hill) National Park - Lawn Hill Gorge, Queensland

Lawn Hill Gorge is located 340 km north-west of Mt Isa and 220 km south-west of Burketown. The access from Burketown and 215 km of the road from Mt Isa is unsealed and inaccessible after rain (the Wet season is November-April). The best road conditions are found via Cloncurry along a sealed road to Gregory Downs with 100 km of gravel road thereafter. Lawn Hill Gorge is formed by Lawn Hill Creek, which is spring-fed from the limestone plateau to the west. The gorge is lined by sandstone cliffs as part of lthe ancient sandstone of the Constance Range and forms an oasis is a typically arid surrounding landscape. There is a campground with toilets and showers Access to the Park around the Gorge is along 6 marked walks varying from 1 - 4 hours of walking time.

Identification

Males  to 7.1 kg (average 5,4 kg) and females to 5.7 kg (average 3.6 kg).   The Purple-necked Rock-wallaby is pale grey with dorsal brown marbling.  The fur is short, dense and soft. The undersides are a pale grey with a brown tinge.  The rump and base of the tail are red-brown. The face is predominantly brown with a black muzzle and dark-brown nose. The upper lip is marked by a light strip. The head is dissected by dark stripe from the eyes back to the ears.  The common name derives from purple-mauve pigmentation over the face, head, throat, neck and on some individuals across the chest and shoulders.  The colour varies from faint pink to deep red-purple according to season and individual variation. The back of the ears are dark to red brown. The fingers and hind feet are dark brown. There is a dark patch in the armpit but no side stripe.  The anterior part of the tail is a lighter grey than the body but terminates in dark hairs with some elongated gold-brown hairs forming a slight brush.

Habitat

In common with other Rock-wallabies, the Purple-necked inhabits rock outcrops, boulder piles, cliffs and gorges. These are formed from limestone, sandstone or quartzite and generally covered with dry Eucalypt (e.g. Coolibah,  Kalumburu Gum, Boxes, Bloodwoods and Ghost Gum) and Acacia woodland, with an understorey of spinifex (Triodia) and with Figs (Ficus spp.) and a diversity of species in moister gorges. Its arid habitat constrains activity during the day and it usually only emerges from cool, deep shelter sites after dark. In winter, they may be visible sunbathing in the early morning after a night's foraging.

Foraging behaviour

Purple-necked wallabies eat grass and browse although there diet has not been well-studied. They gain water from drinking, dewfall and forage. They may ultimately be dependent on permanent water with the suggestion that more remote colonies die out in extended drought without access to free-water.

Reproductive behaviour

Reproduction has been studied in a sample of Purple-necked Rock-wallabies held in captivity. The  characteristics are an oestrus cycle of 36-38 d, post-partum oestrus, embryonic diapause, a pouch life of 6-7 months, with weaning 3-6 months after permanent emergence from the pouch. Females are sexually mature at 18 months and males at 22 months. Breeding is continuous. Courtship and mating are typical of rock-wallabies with males associating with females, following them and sniffing the pouch and cloaca.

Social organisation

Rock-wallabies are typically social and live in colonies varying from a few individuals to over 100. The social organisation of the Purple-necked Rock-wallaby has not been thoroughly studied but it typically lives in small groups ranging to more than 20 individuals.

Further readings

Eldridge MDB, Johnson PM, Clancy TF, Bell JN, Close RL (1993) Identification of a rock-wallaby from "Lawn Hill", north-west Queensland as Petrogale lateralis purpureicollis: a significant range extension. Australian Mammalogy 16, 59-60.

Eldridge MDB, Wilson ACC, Metcalfe CJ, Dollin AE, Bell JN, Johnson PM, Johnston PG, Close RL (2001) Taxonomy of rock-wallabies, Petrogale (Marsupialia: Macropodidae). III. Molecular data confirms the species status of the purple-necked rock-wallaby (Petrogale purpureicollis Le Souef). Australian Journal Of Zoology 49, 323-343.

Johnson PM, Delean S (2002) Reproduction in the purple-necked rock-wallaby Petrogale purpureicollis Le Souef (Marsupialia: Macropodidae) in captivity, with age estimation and development of pouch young. Wildlife Research 29, 463-468.

Johnson PM, Eldridge MDB, Kiernan V, Cupitt RJ (2001) Significant range extension of the purple-necked rock-wallaby Petrogale purpureicollis. Australian Mammalogy 23, 71-73.