GILBERT'S POTOROO - AUSTRALIA'S MOST ENDANGERED MAMMAL
Potoroo Facts - The Biology and Ecology of Gilbert's Potoroo
What are Potoroos
Potoroos belong to a small family called the Potoroidae (rat-kangaroos), within the large superfamily Macropodoidea. The rat-kangaroos are small marsupials which hop on their hindfeet, dig for much of their food with well-developed forefeet, and have a complex stomach that allows them to extract nutrition very efficiently from their diet. The Potoroidae contains several small genera, including Bettongia, (the bettongs, such as the burrowing bettong and the brush-tailed bettong) and Potorous, containing the potoroos.
Altogether, five types of potoroo have been described. Two of these, Potorous tridactylus apicalis, from Tasmania, and Potorous tridactylus tridactylus, from South-eastern Australia, are regarded as subspecies of the Long-nosed Potoroo P. tridactylus. In wet forests of Gippsland in Victoria and southern New South Wales, a few hundred Long-footed Potoroos Potorous longipes hang tenuously onto existence. The Broad-faced Potoroo Potorous platyops was the only potoroo known to live in semi-arid habitats, but no living animals have been recorded since the 1870s, although the sub-fossil remains that have been found show that it was widely distributed in southern and western coastal parts of Australia. Gilbert's Potoroo Potorous gilbertii is the fifth member of this exclusive group.
A medium-sized mammal slightly smaller than a rabbit and bearing some resemblance to a bandicoot, Gilbert's Potoroo has a dense coat of soft grey-brown fur. The tail is lightly furred, and curls up tightly when the animal is at rest. When standing, the animal has a hunched appearance and its eyes appear to look obliquely upwards. The sides of the face are furred giving the appearance of heavy jowls and the snout is slender, curving slightly downwards as in other potoroos. The ears are rounded and almost completely buried in the fur.
The forefeet have long curved claws, forming strong digging appendages that are also able to handle food items with great dexterity. The hindfeet are long, as in the other members of the kangaroo family. Gilbert's Potoroos place their fore-feet on the ground when moving slowly, but hop on their hindfeet when moving rapidly.
Gilbert's Potoroo is now known only from the Mount Gardner headland at Two Peoples Bay. Within that small area (1000 ha), it occurs in at least five separate patches of long-unburnt, dense shrubland on the valley slopes. The number of known individuals depends on both the actual population and the trapping effort. Trapping is conducted in all the major sites of suitable habitat on Mount Gardner and it is likely that the majority of Gilbert's Potoroos have access to established trap sites. It is very unlikely that there are more than 30 to 40 animals in the only known wild population.
Trapping and radio-tracking have shown that Gilbert's Potoroos live in small groups in the patchy habitat. These colonies are isolated from each other but dispersing sub-adult animals and some older males move between them. Amongst resident animals there is little overlap in home range between animals of the same sex, but there is strong overlap between males and females. Gilbert's Potoroo males have home ranges of 15-25 ha (measured over two weeks in summer), whereas females, young-at-heel and sub-adult animals of both sexes move within only 3-6 ha.
Found today in dense long-unburnt shrubland on the flanks of Mount Gardner, Two Peoples Bay Nature Reserve. Preferred habitat is tall shrubland dominated by Melaleuca striata between 1.5 and 2 metres tall, forming a 70-100% canopy cover over dense sedges including Lepidosperma and Anarthria. This grows on deep sandy soil on the slopes of valleys running between the granite ridges on this rocky headland.
The only detailed historic account records the species living in dense vegetation of different species composition lower in the landscape. The original collector, John Gilbert (quoted by Gould, 1863) reported that the Potoroo was found in "the dense thickets of spearwood and rank vegetation bordering swamps and running streams" and that it was "the constant companion" of the Quokka Setonix brachyurus. Quokka populations occur in all areas on Mt Gardner where potoroos have been found and it is likely that many of the runways used by Gilbert's potoroo are 'dual-use pathways' maintained by the larger quokka. Vegetation that forms potoroo habitat at Two Peoples Bay has not been burnt for at least fifty years and it is likely that long-unburnt areas are necessary to support the species.
The potoroos nest during the day and at times during the night in bowl-shaped depressions beneath the spreading sedges, generally well hidden beneath the shrub canopy.
The fruiting bodies of underground fungi (sometimes called "truffles") make up over 90% of the diet of Gilbert's Potoroo, all year round. Other food items, such as berries, fleshy seed-pods and insects are sometimes eaten but only in small quantities. This diet makes Gilbert's Potoroo one of the most fungi-dependent of mammals anywhere in the world. Truffles contain the spores of the fungus but do not open to disperse them, like mushrooms, toadstools and puff-balls. Instead, these fungi disperse their spores by placing them underground in attractive nutritious morsels to be dug up and eaten by mammals. The spores pass through the gut and are dispersed far from their origin in the faeces of the truffle-eater. Gilbert's Potoroos feed by digging truffles mostly from the upper 10 cm of the soil. In doing this, the potoroos leave small diggings but these are hard to tell apart from those of bandicoots.
A recent study by Honours student Vinh Nguyen found spores from 44 species of fungi in the faeces of Gilbert's Potoroos at Two Peoples Bay. Five of these spore-types were found to be consumed by over 60% of animals in all seasons of the year.
The age of sexual maturity for Gilbert's Potoroo is known only approximately. Females can produce young at 750g, when they are less than 12 months old, but males apparently do not mature until they reach around two years of age.
Female Gilbert's Potoroos can produce young at any time of year. Young are born 4-6 weeks after mating and are approximately 1 cm long at that stage. They spend three to four months in the pouch before coming out for the first time at around 150g body weight. Within a week, at around 190g, they have permanently left the pouch, although for around a month they will still suckle from the mother. Young potoroos begin to eat solid food as soon as they leave the pouch and over the next few months they gain, on average, 6g/day. They remain in their mother's home range for another month or two but at about six months of age, when their weight reaches 500-600g, they will leave.
Gilbert's Potoroos exhibit embryonic diapause, whereby the young conceived can develop normally or can be kept in a temporarily suspended state of development. A female brought into captivity with a small pouch young, which was subsequently lost, produced a new young without having contact with a male. A second female, which had been separated from the male shortly after giving birth, produced another young immediately after the first exited the pouch, again without having any further contact with a male.
Gilbert's Potoroos are relatively long-lived. One female, at least one year old when brought into captivity, is still alive nine years later and so is at least ten years old. One wild male, first captured as a mature adult at least two years old, was last recaptured seven years later and so was then at least nine years old.
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