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

Tasmanian Bettong

Bettongia gaimardi cuniculus ('Gaimard's bettong')

Best place to see

Epping Forest, Tasmania

The Tasmanian Bettong can be seen in a number of reserves and national parks in Tasmania. We have chosen Epping Forest in the Midlands of Tasmania. The town of Epping Forest is about 45 km from Launceston and provides accommodation for the visitor. The original Epping Forest was about 21,000 ha. Little of that forest now remains but a reserve of about a thousand hectares, called the Tom Gibson Reserve, conserves the dry woodland and forest, which is relatively unique to the Midlands area. This dry vegetation type is favoured by the Tasmanian Bettong. The site has been used for many studies of the species and first interest in reserving parts of the original Epping Forest were prompted by knowledge of its importance to the Tasmanian Bettong.

Identification

The Tasmanian Bettong is the largest of the Bettongs averaging around 1.7 kg and reaching 2.2 kg. Apparently the mainland specimens which had been collected were smaller than the Tasmanian specimens but the former are of course now extinct. The colouration of the back and head is grizzled from pale to medium brown-grey. The ears are hairy in the back and of the same colour as the head. The nose, as is typical of Bettongs, is naked and brown in colour. The underside is a pale grey, with some hair having a white base. The tail has a weak crest, unlike be Brush-tailed Bettong, and the tip is often white. Both the fore legs and the hind legs are white or cream-white and a characteristic is that the central claws of the fore-paws are very long and curved, and presumably quite adept at digging.

Habitat

The typical habitat of the Tasmanian Bettong is dry sclerophyll forest. These forests are found in areas of low fertility in the northern, eastern and central parts of Tasmania. The general characteristic of these forests is that they are either heathy or grassy. Heathy forests are dominated by Allocasuarina, and the Eucalypts Black Peppermint and Silver Peppermint whereas the grassy forest is dominated by the Eucalypt, Swamp Peppermint.

Foraging behaviour

The Tasmanian Bettong eats seeds, roots and tubers, the bulbs and exudates of some plants, both hypogeous and epigeous fungi, and some invertebrates like insects and gastropods. The diet varies with season, but throughout the year about between 78% and 97% of faeces in a study in dry sclerophyll eucalypt forest contained fungi. The diversity of fungi is quite high in summer with about 46 spore types.

The ability of Tasmanian Bettongs to find buried fungi and the chemical nature of the compounds which alert them to these fungi have been studied in captivity. The Bettongs dug directly over the buried fungi more often than buried glass marbles or simply disturbed soil and the odour of the fungi were sufficient to attract them because they would dig over buried filter paper on which there was an extract of the fungus. It appears that Tasmanian Bettongs respond to volatile compounds in the fungi as a combination rather than individual compounds. If they are presented with separate volatile compounds then they have a poorer ability to discriminate where the fungi are buried than provided with a mixture of volatile compounds. The European commercial black truffle, which is so valuable to the restaurant and gourmet food trade also has this combination of volatile compounds. Amongst these compounds dimethyl sulphide, which gives them a powerful odour, mainly  attracts animals. The fungi tested in Australia didn't produce this particular compound, so it would seem that if you are going into a commercial truffle industry you would not have a particular problem with Tasmanian Bettong. Rather the Bettongs are important in dispersing the spores of fungi which form mycorrhiza with the roots of trees and shrubs and assist the plant to take up nitrogen for growth. Thus they are key to maintenance of forest health and productivity.

Tasmanian Bettongs survive low to moderate fire and there may be a transitory increase in population density on burnt areas. Trials to determine whether fire stimulates the production of fruiting bodies of fungi have been ambiguous. Fire clearly increases Bettong diggings and foraging activity and this may reflect exposure of a variety of buried food sources when fire strips off ground cover. Frequent fire is detrimental to fungal production which is highest in sites that have not been burnt for four or more years. Thus the Bettongs are advantaged by recent fire but not frequent fire.

Reproductive behaviour

The Tasmanian Bettong like most of the rat-kangaroos has a gestation period (21 d) just shorter than the oestrous cycle (23 d) and thus has a post-partum oestrus with mating taking place very soon after the current pouch young vacates the pouch permanently. They show embryonic diapause and breed continuously regardless of season. Pouch life is around 15 weeks and thus they are able to produce more than one young per year. Early in pouch life a watery protein-rich milk with high levels of carbohydrate but little fat is provided. Towards  the end of pouch life the amount of fat in the milk increases and carbohydrates drop.

The Tasmanian Bettong is not sexually dimorphic and ardent males are repelled by similar sized females with kicks from a sideways prone position if the female is unreceptive. As the female approaches oestrus (receptivity) she and her male consort hop around in tandem until the male mounts grasping the female around the flanks with his forelimbs. The male may grasp and bite the female's neck to hold the mounting position leaving a disturbed patch on the female's back as evidence of mating. Females are relatively intolerant of each other and males. Thus individuals appear to defend nest sites and foraging areas. Sexes associate only for mating purposes.

Social organisation

Tasmanian Bettongs are a small herbivore and might be expected to live in fertile habitat with high quality food. However, the opposite seems to be true with selection of habitat with infertile soils and open rather than dense undergrowth. Abundance is a function of vegetation communities with extensive mycorrhizal root development on soils of low fertility. The Bettongs are supported in the habitats by the fruiting bodies (sporocarps) of mycorrhizal fungi.

Home ranges of males are larger than females and encompass the nesting sites of multiple females. Home ranges size ranges from 35-45 ha and movements of 500-600 m in an hour are not unusual. Individuals have multiple nest sites which may be clustered in one end of their home range. They use a nest site for a few nights and then move on to another. Different sets of nests may be used in different months perhaps reflecting climatic conditions in their cool temperate environment. An individual may defend an occupied next against another Bettong but the nest sites of neighbouring individuals overlap. Activity is predominantly at night with a rest period in the middle of the night. Males may spend part of the night visiting females to detect oestrus. 

Further readings

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

Donaldson R, Stoddart M (1994) Detection of hypogeous fungi by Tasmanian bettong (Bettongia gaimardi: Marsupialia; Macropodoidea). Journal Of Chemical Ecology 20, 1201-1207.

Johnson CN (1997) Fire and habitat management for a mycophagous marsupial, the Tasmanian bettong Bettongia gaimardi. Australian Journal of Ecology 22, 101-105.

Rose RW (1986) The habitat, distribution and conservation of the Tasmanian Bettong, Bettongia gaimardi (Desmarest). Australian Wildlife Research 13, 1-6.

Taylor RJ (1993) Home range, nest use and activity of the Tasmania bettong, Bettongia gaimardi. Wildlife Research 20, 87-95.