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

Narbalek (Kimberley)

Petrogale concinna monastria ('elegant rock-weasel')

Best place to see

Bonaparte Islands (Augustus), Western Australia

Augustus is a 17,952 hectare island in the Bonaparte Archipelago off the Kimberley coast. The island arose through the sinking of the coastline and so carries an intact flora and fauna from the mainland. The island may be reached by boat and from charter companies servicing the Kimberley coast. The Narbalek is also recorded from Borda Island to the north and Kalumburu on the mainland and in the nearby Drysdale River National Park. Access to the Drysdale River National Park is extremely difficult and through private property (Carson River Station) with permission. There are no visitor facilities in the Park. The Kimberley Narbalek can also be found at Wyulda Creek in the Prince Regent Nature Reserve in sympatry with the Short-eared Rock-wallaby but not the Monjon which is also found in this reserve.

Identification

Males and females average 1.3 kg in the dry season and 1.4 kg in the wet season. The maximum recorded weight is 1.7 kg. Thus the species is also known at the Little Rock-wallaby.

The fur is long and dense and the back is rufous overlain with white and dark brown to black marbling.   The marbled appearance arises from longer hairs which have a dark brown base, a long white central band and a dark brown to black tip.  The underfur is likewise dense and grey-white.  The cheeks and head are grey with an orange tinge and the head is dissected by a darker dorsal stripe from between the eyes to the nape.  There are indistinct broad stripes across the side of the face from the nose to the front of the eyes. The upper one is dark grey with an orange tinge and the lower one more yellow.  There is some variation in the colour of the nape and shoulders from rufous to rust-red.  The nose is naked and black. The  fur is relatively sparse on the upper half of the ears and the inside of the ears is is defined by sparse white hairs. The arms, legs and feet are fawn merging to grey on the hands and feet.  The undersides are yellow-grey.  The tail gradually darkens towards the tip as longer dark brown to black hairs increase.  About the distal third  of the tail has a pronounced brush.

Habitat

The habitat of the Kimberley Narbalek varies according to site in the region. A consistent feature is that it found in rugged King Leopold Sandstone boulder and gorge country. There is usually a hummock grassland of Plectrachne spp. with sparse figs. The rocky areas are typically bordered by low open woodlands of various Eucalypts and Emu Apple (Owenia vernicosa). On August Island it has been seen near mangroves along the coast.

Foraging behaviour

You are unlikely to make a dental examination of a Narbalek but it is something of a shark amongst marsupials. It has an unlimited number of molars which shuffle forward along the tooth row as the frontal ones are worn down and lost (the analogy with sharks is this repetitive tooth replacement). The Narbalek early dispenses with its pre-molars and usually has four to six molars in play in each quadrant of the mouth. This unique dentition is an adaptation to a diet of highly silaceous (15-20% dry weight of silica) grasses and the fern Marsilea crenata at least on the floodplain sites in the NT where Narbalek diets were studied. You are more likely to see Narbaleks during the day in the Wet season when they may bask on the rocks in the morning and forage in the late afternoon. In the Dry season foraging is predominantly nocturnal and body condition may diminish as the seasonal drought hardens.

 

Narbaleks may forage with other rock-haunting macropods, especially Short-eared Rock Wallabies. The Narbalek is only the size of a juvenile of the latter species and is much faster and more agile.

 

Reproductive behaviour

Narbaleks breed throughout the year but are more likely to have a large pouch young or young-at-foot in the core of the Wet season (February) than the Dry season (August). In captivity, embryonic diapause has been demonstrated with gestation lasting 30-32 d and an oestrous cycle of 32-35 d with a post-partum oestrus. Pouch exit is at about six months and sexual maturity is achieved after a year.

Social organisation

The social organisation of Narbaleks is not well-described. They forage well out from rock shelters and may associate together and with other rock-wallaby species. The sexes intermingle on foraging sites.

 

Further readings

Churchill S (1997) Habitat use, distribution and conservation status of the Narbalek, P. concinna, and sympatric rock-dwelling mammals, in the Northern Territory. Australian Mammalogy 19, 297-308.

Nelson JE, Goldstone A (1986) Reproduction in Peradorcas concinna (Marsupialia: Macropodidae). Australian Wildlife Research 13, 501-505.

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

Sanson GD, Nelson JE, Fell P (1985) Ecology of Peradorcas concinna in Arnhem Land in the wet and dry season. Procceedings of the Ecological Society of Australia 13, 69-72.