It is nearing the end of the dry season on the Mitchell Plateau in the Kimberley of Western Australia. The vegetation of the woodlands and surrounding the exposed boulders is desiccated and expectant. The temperature on this afternoon is in the high thirties and the humidity is building daily.
Deep within a narrow vertical fissure of a huge sandstone boulder a female Scaly-tailed Possum lies sleeping. The climate in this fissure is relatively cool and damp, allowing a proliferation of ferns to reach full potential about the margins of this fissure.
The female Possum had been feeding the previous night on the blossoms and foliage of the Eucalypt and Terminalia trees that were growing adjacent to the nesting fissure. The feeding had been adequate, in that it provided for her needs and those of her single pouch young.
It is now late October, the male joey had been born some four and a half months previously and had first opened his eyes a month ago. Another three to four months will pass before this joey will be weaned and commence feeding on a diet of fruit and blossoms, leaves and insects. Her previous young had been lost when it ventured too far from the safety of her pouch and was taken by an Olive Python.
This male joey was well furred with a dorsal coat of fine pale grey hair not unlike that of his mother, which had a fully developed coat of pale grey tipped with black with a faint dark stripe running from her shoulders to her rump. The joey bore the hallmark of his kind – a finely developed scaly tail, the surface of which gave the appearance of a metal file. Like his mother, his ears were short and bore a close resemblance to those of his relatives, the Cuscuses.
When darkness descended the female Scaly-tail left the fissure which provided relative security during the daylight hours and commenced her evening foraging. The temperature and humidity were still high, unlike the atmosphere maintained in the depths of the King Leopold sandstone formation. This evening she began her search for fruits and blossoms in a large patch of deciduous vine thicket, the Kimberley equivalent of tropical rainforest. The boulder sandstone formation maintained the moisture levels of these thickets and allowed for a profusion of vines, shrubs and trees. The coming of the monsoon would bring about a more varied selection of
fruits and blossoms for the possum and other fauna of the plateau.
Although her primary task was to satiate her hunger, she maintained a watch for night predators, particularly for those with silent wings, the owls. Although other predators would attempt to take her kind in the night, namely the Dingo and the Northern Quoll, the female bore an instinctive fear for the owls. Some months ago she had emerged from the refuge at sunset and was about to scale a eucalypt when she saw about her a Barking Owl tearing a young male of her kind to pieces. On this occasion, she instinctively dived for the safety of her rock fissure, not emerging again until long after the owl had left the area.
The night passed without incident apart from meetings with other night foragers, namely a Woodward’s Rock-rat and a Northern Brown Bandicoot. On her return to the fissure in the early hours of the morning, the female Scaly-tail passed another denizen of the boulders – a Warabi, a rock-wallaby which had its day refuge in a horizontal crevice a short distance away.
Some hours after returning to the fissure, the female possum was startled by strange vibrations coming through the very rock itself. She had never experienced this sensation before and she was totally perplexed – whether to flee or remain still. Unknown to the Scaly-tail and unseen by her kind, members of another species of mammal had commenced their invasion of the ancient plateau. The vibrations had been caused by seismic explosions carefully laid on a bulldozed scar across the plateau. These humans were the forerunner of a multitude that would descend on the plateau to remove vast deposits of bauxite from the ancient formations of the Mitchell Plateau.
The History of Collection
The animal was first described in 1919 by the Keeper of Biology at the Western Australian Museum, Wilfred Backhouse ALEXANDER (1885 – 1965) based on a specimen from the Perth Zoo. This specimen was said to have come from Violet Valley Station in the East Kimberley, an Aboriginal reserve located between Wyndham and Halls Creek. The locality for this original specimen appears to be erroneous based on the low rainfall (600mm per annum) compared to known locations.
Alexander created a new genus for this animal which he gave the name WYULDA. This name seems to have been applied in error as Wyulda was the Aboriginal word for the Northern Brushtail, Trichosurus arnhemensis. The Aboriginal word for the Scaly-tailed Possum, according to a Worora legend narrated to H.H. Finlayson, the famed South Australian zoologist, was ILANGURRA (Burbidge (1983) gives the word as ILLUNGALYA in Strahan). The specific name “squamicaudata” includes two Latin words “squama’ for scale and “cauda” meaning tail. Alexander is to be forgiven for this error as he had only arrived at the W.A. Museum in 1912 after graduating in natural science from Cambridge University.
A second specimen was sent to Finlayson by the Reverend J.R.B. Love, collected at the Presbyterian mission at Kunmunya by the local Worora tribes people. Kunmunya Mission was situated about 400 kilometres along the coast from Derby. Further specimens were not obtained until 1954 when Ken Buller of the W.A. Museum collected a female with pouch young at Wotjulum Mission halfway along the coast between Kunmunya and Derby. Based on these scant records the Scaly-tailed Possum was thought to be a rare species. Another specimen taken by the local wharfinger at Broome on the Dampier Peninsula is now thought to be an erratic record, the specimen possibly transported to Broome from Kalumburu. In December 1965, however, the species was found to be locally common at Kalumburu in the north Kimberley by the now well-known media personality, Harry Butler (W.H. Butler). Butler trapped a total of eight specimens on this occasion on behalf of the American Museum of Natural History and the W.A. Museum. A juvenile female was the sole survivor of this collection and this lived for 6 years in the care of artist Ella Fry. Between September 1981 and December 1982, a total of 19 individuals were studied in situ on the Mitchell Plateau in the north-west Kimberley, an area where they were found to be locally common.
The Scaly-tailed Possum is endemic to the Kimberley in Western Australia.
Site records indicate that this possum is confined to coastal portions of the west, north-west and north Kimberley and a few islands adjacent to these coastal portions. Areas of particular importance in relation to present distribution appear to be the Prince Regent River Reserve and the Mitchell Plateau in the North-west Kimberley and the area around Kalumburu at the northernmost point in Western Australia. The Possum has been recorded on both Boongaree and Bigge Islands. A general rule appears to be that the Possum is restricted to areas receiving in excess of 900 mm rainfall.
Detailed descriptions of the Scaly-tailed Possum appear in Alexander (1919) and Finlayson (1942). In general terms, this possum bears a resemblance to both the Brushtail Possums and the Cuscuses, the latter by virtue of the naked, prehensile tail.
The maximum dimensions are as follows:-
Head and body length – 400 mm
Tail length – 300 mm
Weight – 2.0 Kg
There appear to be no difference in dimensions between, male and female, nor do there appear to be differences in coat colour. The body fur is described as being fine, dense and short and of a pale grey colour above and creamy white below with a yellowing of the fur about the pouch opening. There is a faint dark dorsal stripe running from between the ears to the rump. The head is described as being flat with small ears which are slightly longer than they are wide. The eyes are large, of a dark brown colour and protruding. The flattened head may be an adaptation to its living in rock fissures etc. as is a feature of the Planigales.
The part of this possum’s anatomy which gave rise to its specific name, the scaly tail, is of great interest. The fur at the base of the tail is of a rufous colour – four fifths of the tail is near naked. The scaly appearance of the tail is due to the raising of the skin into tubercles, each of which is surrounded by tiny, coarse, black hairs. The tail is said to have a ‘rasp-like appearance’. The underside of the tail extremity is described as being free of tubercles and prehensile.
Areas and populations studied seem to indicate that populations may reach a density of one animal per hectare with an equal spread of males and females. The Scaly-tailed Possum appears to be a slower developer than other possums. This possum appears to breed in its third year, whereas the Northern Brushtail will breed in its second. Indications are that females to be in breeding condition will exceed 1100 9 in weight, with males probably exceeding this weight. The breeding season appears to be restricted to the period from March to August. This indicates that there are restrictions imposed on breeding at the end of the dry season a time of particular stress, and throughout the height of the monsoon (December to March). Indications are that
young may not leave the pouch until they are 200-210 days old, with lactation possibly continuing until the young is at least 250 days old. The majority of the population and reproduction biological findings relate to work carried out during the 1981/1982 Mitchell Plateau study.
Deeply dissected boulders in the King Leopold Sandstone areas of the coastal Kimberley supporting deciduous vine thickets and open woodlands.
The Scaly-tailed Possum is referred to as being, ‘probably omnivorous, dominantly herbivorous’. The possum has been observed feeding on blossoms and foliage of Eucalyptus spp. (particularly Bloodwoods). Other sources of food are probably the fruits, blossoms and leaves of Ficus spp.; Terminalia spp.; Owenia vernicosa (the emu apple); Adansonia gregorii (the baobab) and Acacia spp. In captivity these possums have taken peanuts, fruit (banana, paw-paw, tomato, guava, apple) bread and honey, boiled egg, mealworms and blossom of the red-flowering gum. Also in captivity this animal has been observed to cache peanuts.
The Scaly-tailed Possum is predominantly nocturnal. The possibility exists that it may forage during the day when the wet season has set in due to heavy cloud cover (C. Kemper, S.A. Museum: pers. comm.). The animal appears to be solitary despite the fact that relatively large numbers occupy small areas of quality habitat. It is assumed that this Possum spends a fair proportion of its time on the ground, hence the modifications to the feet pads. When disturbed while feeding in trees, this animal will descend immediately and seek shelter in rock fissures, etc. This Possum has been heard to emit an alarm call – a ‘bird-like’ chittering, chirping noise. When handled the Scaly-tailed Possum is said to be extremely aggressive – it bites, hisses and scratches. Zoologist R. A. How has remarked that of a number of species that he has handled as part of field studies, this possum had been the most difficult to handle (C. Kemper: pers. comm.). It is noteworthy that although the geographical distributions of the Scaly-tailed Possum and the Northern Brushtail overlap, there appears to be a distinct habitat separation. T. arnhemensis on the Mitchell Plateau was only located in mangroves, one kilometre from the shoreline (C. Kemper: pers. comm.).
In relation to the prehensility of the tail, it is not known whether the tail would bear the full bodyweight of the animal. Previous work suggests that the proximal portion of the tail is prehensile, thus indicating a lack of fully prehensile capacity.
Based on previous observations and species lists the following vertebrate species may prey on either juvenile or adult Scaly-tailed Possums.
Dasyurus hallucatus : Northern Quoll (Juveniles only?)
Canis familiaris dingo : Dingo (Adults and juveniles)
Aquila audax : Wedge-tailed Eagle
Ninox rufa rufa : Rufous Owl
Ninox connivens connivens : Barking Owl
Morelia spilotes variegata : Carpet Python
Liasis olivanceus : Olive Python
Varanus gouldii : Gould’s Goanna
The first specimen of W. squamicaudata was held in captivity at Perth Zoo in 1917. In 1965 Mrs. Ella Fry received a juvenile female which thrived in her care for a period of six years. Animals have been kept as pets at the Kalumburu Missions and these in turn have been supplied to Perth Zoo. A pair of these possums was being maintained at this zoo in 1979. Problems have been encountered in relation to respiratory diseases (e.g. fibrinous and bronchial pneumonia) caused by lung mite. Tropical temperatures and humidity appear necessary for successful maintenance. The diet as previously stated with the addition of multi-vitamin and soft-bill mixture appears satisfactory.
Statements have been made to the effect that the Scaly-tailed Possum varies in status from rare to common in limited areas. It has also been stated that the habitat of this possum is secure. The habitat of this species is certainly remote but as displayed by the current range shrinkage of Isoodon auratus, the Golden Bandicoot, which shares a proportion of the Scaly-tailed Possum’s habitat, the remoteness of the habitat is no guarantee for species security. Current knowledge in relation to Wyulda squamicaudata is based on observations in relation to probably no more than 35 individual specimens, both living and deceased, according to the literature. All projections in relation to population size are based on these observations – a scant basis for species conservation. The population in the Prince Regent River Reserve would appear to be secure by virtue of habitat conservation, however, large populations do not appear to have been observed there. The Kalumburu habitat does not fall within a conserved area, nor does that of the Mitchell Plateau. A major conservation battle appears likely with respect to the Mitchell Plateau due to bauxite miming proposals. These appears to be no room for complacency in relation to this unique inhabitant of the King Leopold Sandstone of the Kimberley. Certainly this possum merits further behavioural and biological studies before conclusions can be drawn with respect to its conservation.
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Cogger, H.G. (1975). Reptiles and Amphibians of Australia. A.H. & A.W. Reed, Sydney.
Fairfax, R.A. (1982). Notes of the Scaly-tailed Possum, Wyulda squamicaudata, in captivity. In Evans, D-D. (Ed.). The Management of Australian Mammals in Captivity. pp, 73-4, Zoological Board of Victoria, Melbourne.
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