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 Bettongs, Potoroos and Musky Rat-Kangaroo are collectively known as the Rat-kangaroos. In fact, they form two families, the Potoroidae, which includes all the potoroos and bettongs, and, the Hypsiprimnodontidae, whose sole living representative is the Musky Rat-kangaroo. They are observationally distinguished from the kangaroos and wallabies by their diminutive body size but the largest species, the Rufous Bettong, eclipses the smallest Rock-wallabies, the Monjon and Narbelek. In general, they retain more 'primitive' ancestral characteristics with a partly prehensile tail to entrap grasses and sticks for nesting and a simpler stomach (and consequently richer diet). The forelimbs and hindlimbs are more similar in size than the gross differences in the kangaroos and wallabies, and so bounding as well as hopping is a mode of progress. Perhaps possum-kangaroo is more accurate but the first European observers were more familiar with rats than possums.

If you find an intact skull on your exploration of rat-kangaroo habitat then the dentition is clearly distinguishable from the kangaroos. They are more buck-toothed with the second and third incisors smaller than the first and more lateral in the upper jaw. The upper canines are well-developed whereas they are lost in the Macropdodidae. The premolar is large and blade-like and the molars are retained rather than lost anteriorly through wear and progress along the tooth row.

The rat-kangaroos have fared very poorly with the advent of agriculture and pastoralism compounded by the introduction of competitors (European rabbits and hares) and predators (Red foxes and domestic cats). The Potoroids generally have much reduced ranges relative to the first settlement of Australia by Europeans and two of the 10 species are extinct. The most dramatic of the declines is the Boodie (Burrowing Bettong) which was widespread across the rangelands of Australia and ended up marooned on a few offshore islands in Western Australia. Reintroductions are in progress and this species is on the first hops to making a comeback on the mainland. Like the Potoroids, the Musky Rat-kangaroo has lost much of its habitat in the highly prized real-estate of the tropics.

Species

Musky Rat-kangaroo

Hypsiprymnodon moschatus ('high rump and musky odour')

Best place to see

Crater Lakes National Park, Queensland

The Crater Lakes National Park has two sections - Lake Barrine and Lake Eacham. Both Lakes are within the Wet Tropics World Heritage area. The Lakes are fringed by rainforest where the Musky Rat-Kangaroo and Red-legged Pademelon can be seen by day. At night, Lumholtz's Tree-kangaroo may be viewed along the various walking trails at each Lake. The Park does not have accommodation or camping but is near Cairns and other locations in the Atherton Tablelands of Queensland that have a full range of accommodation.

Identification

Musky Rat-kangaroos are the smallest of the macropods and average 0.5 kg and reach a weight of 0.7 kg. The Hypsiprymnodontidae is the most primitive Family in the Macropodoidea and the Musky Rat-kangaroos is the sole surviving member of the Family and its genus. The key characteristics of the Family are almost equally long fore- and hind-limbs so that the gait is generally bounding and quadrupedal rather than hopping. The first toe of the hind foot is mobile and functional but does not have a claw (digit 1 is absent in all other macropods). The largest toe (digit 4) is not as elongated as in other macropods. The general colour of the Musky rat-kangaroo is a rich, dark red brown with dark brown guard hairs. The fur is soft and dense and the back but shorter on the face and head where it tends to be more grey in colour. The hair on the fore- and hind-limbs is similar to on the back and sides becomes very short near and across the ankles and wrists which are covered in dark-brown hair. The undersides have very soft and dark brown fur unlike the light undersides of most macropods. However, patches of white fur may be present along the centre line of the throat, chest, and upper part of the abdomen but this character is highly variable and may be absent. The body hair ends abruptly about 10 mm long from the tail base and the remainder is covered with scales and thus appears to be naked. However, there are very short hairs scattered rather sparsely amongst the scales. The tail is dark brown and the dorsal surface is somewhat darker than the under surface. In contrast to Potoroos and Bettongs, the claws on the fingers are relatively short.

Habitat

The Musky Rat-kangaroo inhabits tropical rainforest with a diverse overstorey of trees that supply its mainly frugivorous (fruit-eating) diet. The main vegetation type is a complex mesophyll vine forest in both tablelands and coastal areas. Habitat fragmentation through clearing for livestock grazing and agriculture and horticulture has severely reduced its habitat. In the tablelands fragmentation leads to local extinction and persistence in only very large fragments of intact forest.

Foraging behaviour

The diet of the Musky Rat-kangaroo diverges from the other rat-kangaroos as they eat mainly  fruit.  These are supplied by a number of trees such as Figs (Ficus spp.), Quandongs (Silver Quandong - Elaeocarpus augustifolia), Walnuts (Boonjie Blush Walnut - Beilschmiedia volcanii, Hairy Walnut - Endiandra insignis), Lilly-pillies (Watergum - Syzygium gustavioides), and vines like Austrobaileyana scandens).  They also eat seeds with soft coats, roots and tubers, the fruiting bodies of hyopeous and epigeous fungi, and some invertebrates. Unlike other Rat-kangaroos, they forage mainly in the day.

Reproductive behaviour

The Musky Rat-kangaroo like most of the rat-kangaroos has a gestation period (19 d)  shorter than the oestrous cycle (26 d) but has no post-partum oestrus (i.e. mating taking place very soon after the current pouch young vacates the pouch permanently) and no embryonic diapause.  The do not breed continuously but rather males' testes enlarge dramatically in October in advance of the Wet season and shrink (recrudescence) after April when the Dry season commences. Females carry pouch young from March until October with a 5-6 month pouch life so that permanent pouch exit is in the Wet season. They can raise 1-3 young in a single litter. Other Rat-kangaroos can have two young in the pouch from separate oestrous events but rarely raise the smaller of the two to pouch exit.

 

With the increase in testes size and testosterone production, males become more aggressive in the breeding season. They chase other males off but the competition may be resource-based (over fruit) as much as for mates. Fighting is usually a strike with the forepaw and thus relatively less damaging than the other Rat-kangaroos.

 

Social organisation

Musky Rat-kangaroos live at relatively very high densities of 140 - 450 per km² compared to other Rat-kangaroos. Home ranges are thus very small with a mean of 2.1 ha for males and 1.4 ha for females. Both the foraging ranges of individuals and the location of nest sites overlap. This packs more individuals into the habitat allowing high densities. Musky Rat-kangaroos may form small aggregations of 2-3 individuals foraging on fallen fruit.

 

Further readings

Claridge AW, Seebeck JH, Rose R (2007) 'Bettongs, Potoroos and the Musky Rat-kangaroo.' (CSIRO Publishing: Melbourne).

Dennis AJ, Marsh H (1997) Seasonal reproduction in musky rat-kangaroos, Hypsiprymnodon moschatus: A response to changes in resource availability. Wildlife Research 24, 561-578.

Dennis AJ (2002) The diet of the musky rat-kangaroo, Hypsiprymnodon moschatus, a rainforest specialist. Wildlife Research 29, 209-219.

Lloyd S (2001) Oestrous cycle and gestation length in the musky rat-kangaroo, Hypsiprymnodon moschatus (Potoroidae: Marsupialia). Australian Journal Of Zoology 49, 37-44.