In December 1994 Gilbert's Potoroo, Potorous tridactylus gilberti, was rediscovered at Two Peoples Bay Nature Reserve east of Albany, Western Australia. This potoroo was thought to be extinct for 125 years prior to this discovery, and after further inspection, three more animals were captured. In total, two adult males, a sub-adult male, and two females, each with a pouch young, have been captured ( http://www.environment.gov.au/life/end_vuln/animals/potoroo.html 1997 and Strahan 1995). Other common names for P. tridactylus are the Long-nosed rat-kangaroo and the Wallaby Rat (Strahan 1995).
Perception Channels: tactile ; chemical
Potorous tridactylus is still quite common throughout Australia, although it and other rat-kangaroos have experienced population decreases attributed to the following: small size, competition with rabbits for succulent food, the spreading of poisoned bait meant for the population control of rabbits, predation by the introduced European fox and feral cats, and sport hunting (Hume 1982, Matthews 1971, Morris 1965). Most regional populations are relatively secure, since the species occurs in conservation reserves; however, one isolated population in the Grampians region of Victoria is at risk because most of its very localized habitat is outside the National Park boundary (Menkhorst 1995). The frequent occurrence of subfossil remains in cave deposits indicate that P. tridactylus was much more common in the past (Strahan 1995). It is not clear to what extent its decline is the result of human activities, but it is obvious that very large areas of suitable habitat along the eastern coast of Australia have been removed by land clearing (Strahan 1995).
IUCN Red List of Threatened Species: least concern
Potorous tridactylus and other rat-kangaroos have been regarded by farmers as pests because of their affinity for crops (Morris 1965).
The small number and large size of P. tridactylus chromosomes has led to the use of their cells - especially those of the kidney and the testis - in tissue culture studies (Tyndale-Biscoe 1973).
Potorous tridactylus is an omnivore and obtains much of its food by digging shallow holes with the claws of its fore feet (Hume 1982). Plant material - cranberries, fungi, grasses, juicy stems, roots, and tubers - constitute its main nutritional source throughout the year (Hume 1982, Matthews 1971, Morris 1965). Of these fungi are the most commonly eaten, while grasses are eaten only during winter when total food availability is at its lowest levels (Hume 1982). Insects and their larvae compose a meager 1-2% of the winter diet of P. tridactylus, but this can increase to 21% during the summer when insect abundance augments (Hume 1982 and Strahan 1995). Finally, it is interesting to note that in order to obtain a sufficient amount of fungi, potoroos are forced to use a variety of widely scattered feeding areas (Hume 1982).
Potorous tridactylus is widely distributed in southeastern Australia and Tasmania and can be found in coastal New South Wales, southeastern Queensland, coastal, near-coastal, and northeastern areas of Victoria, and the southwestern corner of Western Australia (Census of Australian Vertebrate Species 1995 http://www.erin.gov.au/life/species/fauna/cavs81_mammals.html, Menkhorst 1995, Morris 1965, Strahan 1995, and Walker 1975).
Biogeographic Regions: australian (Native )
Relatively thick ground cover is an essential component of a potoroo habitat; therefore, these animals inhabit forests and woods where above-ground nests of dry vegetation can be built among grass tussocks, under bushes, and in low, thick shrubs (Kowalski 1976, Matthews 1971, Morris 1965, Strahan 1995, Walker 1975). In addition, potoroos utilize a wide variety of wet forest and wet scrub habitats developed on sandy loam soils where annual rainfall exceeds 760 mm (Menkhorst 1995). Finally, P. tridactylus are usually found at altitudes between sea level and 250 m, but they has been observed at altitudes up to 650 m (Menkhorst 1995).
Terrestrial Biomes: scrub forest
Average lifespan
Status: captivity: 14.5 years.
Potorous tridactylus is a rabbit-sized rat-kangaroo with an elongated muzzle (Matthews 1971 and Morris 1965). The length of its head and body is approximately 300-400 mm, while its tail is about 150-260 mm long (Strahan 1995 and Walker 1975). Its pelage is straight, soft, and loose with a grey or a light chestnut brown coloration of its upper parts, a grayish or whitish underside, and often a white tipped tail (Matthews 1971, Morris 1965, and Walker 1975). The median claws of its manus (fore foot) - well adapted for scratching and digging - are very long and sharp (Hume 1982, Matthews 1971, and Morris 1965). Potorous has a downward-curving, semiprehensile tail used for carrying bundles of nesting materials (Matthews 1971 and Morris 1965). Its dental formula is 3/1, 1/0, 2/2, 4/4; it also has well-developed canines and bunodont molars (Morris 1965 and Myers 1997). Potoroos have enlarged hind feet and powerful hind limbs which bestow them with adept hopping abilities at high speeds and a rabbit-like gait at slower speeds (Myers 1997). Finally, P. tridactylus has a well-developed marsupium that opens anteriorly and contains 4 mammae (teats) (Myers 1997 and Strahan 1995). It is interesting to note that P. tridactylus populations show considerable morphological variation (Strahan 1995). Over a distance of only 200 km from the western to the eastern coast of northern Tasmania, the average size of these creatures nearly doubles and their coat color changes from rufous brown to grey-brown (Strahan 1995). In addition, the snout is relatively short in animals from Queensland and increases proportionally in size in more southern populations, being most elongate and narrow in Tasmania (Strahan 1995). Finally, the proportion of individuals with a white tip on their tail increases from zero at the northern extremity of the range to 80% in Tasmania (Strahan 1995).
Potorous tridactylus, or the "three-toed potoroo," is one of the first mammals recorded from Australia (Strahan 1995). Its name comes from an erroneous description in Surgeon-General White's Journal of a Voyage to New South Wales in which he referred to the foot of this creature as having only three toes (due to the conjoining of its second and third digits) (Strahan 1995). Therefore, the syndactylous condition found in P. tridactylus is responsible for the misnomer that has stuck with this animal ever since (Strahan 1995).
Range mass: 0.7 to 1.8 kg.
Other Physical Features: endothermic ; bilateral symmetry
Average basal metabolic rate: 2.556 W.
In eutherian mammals the optimum temperature for spermatogenesis is several degrees cooler than deep body temperature (Tyndale-Biscoe 1973). Therefore, these mammals have developed a scrotum as an adaptation for removing their testes from a region of deep body temperature to one that is cooler and closer to the optimum temperature for spermatogenesis (Tyndale-Biscoe 1973). Potorous tridactylus is a non-eutherian mammal; yet, male potoroos have adopted the above eutherian adaptation. Female potoroos are polyoestrus such that periods of oestrus and progestation alternate cyclically and provide the opportunity to conceive at a second or subsequent oestrus if the first is infertile (Tyndale-Biscoe 1973). The 42 day oestrus cycle of P. tridactylus is at the upper limit of that observed in marsupials, while its gestation period is about 38 days (Menkhorst 1995 and Tyndale-Biscoe 1973).
Sexual maturity among males and females is reached at about 12 months, and reproductive potential is about 2.5 young/year (Menkhorst 1995). Both sexes mate promiscuously, and breeding is continuous throughout the year with peaks in early spring and early summer (Menkhorst 1995).
Females give birth to a single newborn weighing nearly 300 mg . The young suckles in the mother's marsupium for up to 120-130 days (Menkhorst 1995 ; Tyndale-Biscoe 1973). Birth is often followed by a post-partum oestrus; mating at this time results in an embryo which remains dormant until the existing young leaves the pouch naturally or dies (Menkhorst 1995). After the existing young vacates the marsupium or dies, the quiescent embryo resumes development and is born approximately 30 days later (Menkhorst 1995). Interestingly, newborn offspring of P. tridactylus and other marsupials are much less developed at birth than placental offspring, and in fact, they resemble a human fetus after the first trimester of gestation (Myers 1997). After the young potoroo leaves the pouch, it will continue to suckle and finally be weaned after about 170 days (Menkhorst 1995).
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
Average birth mass: 0.333 g.
Average gestation period: 30 days.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (female)
Sex: female: 400 days.
