35.
Gilbert’s potoroo
(Potorous gilbertii)
CR
Overview
This small marsupial is one of the most fungi-dependent mammals anywhere in the world. A mere 40 years after its discovery in 1840, Gilbert’s potoroo disappeared completely, leading researchers to fear it had become extinct, another victim of the changes brought about by European colonisation of Australia. More than a century later, in December 1994, the species was rediscovered in a small area of heath on the slopes of Mt. Gardner, Western Australia. With a global population of less than 100, Gilbert’s potoroo is Australia’s most threatened marsupial, and one of the world’s rarest mammals.
Urgent Conservation Actions
Continuation of existing conservation actions.
Distribution
Australia
Media from ARKive
ARKive image - Gilbert's potoroo standing on its hind legs
ARKive video - Gilbert's potoroo - overview
ARKive image - Gilbert's potoroo
ARKive image - Gilbert's potoroo
ARKive image - Gilbert's potoroo
ARKive image - Gilbert's potoroo feeding
ARKive image - Conservation biologist working with a Gilbert's potoroo
Evolutionary Distinctiveness
Order: Diprotodontia
Family: Potoroidae
Gilbert’s potoroo is a small macropodoid marsupial in the family Potoroidae (potoroos, bettongs or rat-kangaroos). These species 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. Fossil members of this family are known from the middle Miocene of Australia (16 million years ago). 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.

Four species of potoroo are currently recognised: the long-nosed potoroo P. tridactylus from southeastern Australia and Tasmania; the long-footed potoroo P. longipes from the wet forests of Gippsland in Victoria and southern New South Wales; the broad-faced potoroo P. platyops (thought to be extinct since no living animals have been recorded since the 1870s); and Gilbert’s potoroo P. gilbertii.
Description
Size: 
Head and body length: 270 mm
Weight: 900 – 1,100 g
Gilbert's potoroo is a compact marsupial that resembles a cross between a bandicoot and a small wallaby. It is slightly smaller than a rabbit and has a dense coat of soft grey-brown fur. The face is long and pointed with a slender snout that curves downwards. The ears are rounded and almost hidden by the long, soft fur. The tail is lightly furred, and curls up tightly when the animal is at rest.

The forefeet have long curved claws which are used for for digging. The hind feet 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 hind feet when moving rapidly. Males and females are similar in body size.
Ecology
Gilbert's potoroo one of the most fungi-dependent mammals anywhere in the world. Over 90% of its diet is made up of the fruiting bodies of underground fungi (sometimes called "truffles"). Other food items, such as berries, fleshy seed-pods and insects are sometimes eaten but only in small quantities. More than 44 different species of fungi have been identified in faecal samples, many of which are thought to form symbiotic (mycorrhizal) relationships with forest trees and shrubs. These fungi supply nutrients to their host trees and help prevent disease. Thus, by spreading the fungal spores throughout the forest in its faeces, the potoroo plays an important role in maintaining the health of the forest.

Gilbert’s potoroos live in small groups of between three and eight individuals that are generally isolated from one another, although dispersing sub-adult animals and some older males move between them. Within these groups, males have home ranges of 15-25 ha, whereas females, juveniles and sub-adults of both sexes move within only 3-6 ha. There is little overlap in home range between animals of the same sex, but there is strong overlap between males and females.

There is little evidence of seasonality in reproduction of this species, with small pouch young having been recorded in all months of the year. Females begin having young (called “joeys”) at nine months of age. A single young is produced and stays in the pouch for three to four months. Like other Australian marsupials, the females are able to delay the development of the fertilised egg (called “embryonic diapause”) if they have a joey in their pouch. The embryo is ‘reactivated’ if the joey dies, or is almost old enough to leave the pouch. The species is relatively long lived, with maximum longevity of both sexes exceeding 10 years.
Habitat
Gilbert’s potoroo appears to be restricted to regions where rainfall is greater than 1,000 mm a year, probably due to their specialised fungal diet and their habitat preference for dense vegetation. They inhabit dense, low heath on the slopes of Mt. Gardner. The vegetation consists mainly of shrubs between 1.5 and 2 metres tall (dominated by Melaleuca striata). A dense layer of sedges (including Lepidosperma spp. and Anarthria scabra) grows beneath this canopy.

The vegetation that forms potoroo habitat at Two Peoples Bay Nature Reserve has not been burnt for over fifty years. It is likely that long-unburnt areas are necessary to support the species.
Distribution
Gilbert's Potoroo is endemic to the south-western part of Western Australia. It was believed extinct until its rediscovery in 1994. The precise location of its former range is unclear, but remains have been found in the vicinity of King George's Sound (Albany) and between Cape Leeuwin and Cape Naturaliste. It is currently restricted to a small area of approximately 1,000 ha in the Two Peoples Bay Nature Reserve on the Mt. Gardner promontory, near Albany, Western Australia. Within that small area, it occurs in at least five separate patches of long, unburnt, dense shrubland on the valley slopes.
Population Estimate

Fewer than 40 in Two Peoples Bay Nature Reserve plus an additional 40 to 50 animals in two translocated conservation colonies on Bald Island. 

Population Trend
Stable.  All suitable habitats in this species’ tiny range appear to be occupied.
Status
Classified as Critically Endangered (CR D) on the 2010 IUCN Red List of Threatened Species.
Threats
Gilbert’s potoroo was believed extinct for over a century until its rediscovery in 1994. The reason for the species’ decline are unclear, although habitat clearance and changed fire regimes may have destroyed the dense vegetation cover, leaving the species exposed and more vulnerable to predation to introduced predators such as foxes and feral cats.

Today, the greatly reduced and restricted population is at high risk of extinction from stochastic events such as wild-fire and disease. The vegetation at Mt. Gardner is extremely fire prone and a single fire event could potentially wipe out the species (except for the few individuals in captivity and on Bald Island). The species is also in the prey size range of both feral cats and foxes, both of which are known to exist in the Two Peoples Bay area. A further potential threat is dieback disease caused by Phytophthora cinnamomi, which eliminates the plant symbionts of the hypogeal, mycorrhizal fungi, the principal food of Gilbert's potoroos. This has the effect of both removing a food source and altering the vegetation structure. Indeed, potoroos are believed to be present only in areas of the within Two Peoples Bay Nature Reserve that are free of Phytophthora infection.
Conservation Underway
Gilbert’s potoroo has been the subject of a recovery program since the discovery of the only known wild population of about 40 animals at Two Peoples Bay Nature Reserve in 1994. Recovery efforts are co-ordinated by the Gilbert’s Potoroo Recovery Team which includes representatives from Western Australian Department of Environment and Conservation (DEC), Perth Zoo, universities, conservation organisations and community groups.

The recovery programme encompasses managing and protecting the extant population and its habitat (including fire exclusion measures), protecting and rehabilitating bushland corridors in areas adjacent to the reserve (to aid with dispersal), eradicating feral predators (foxes and cats), and captive breeding and reintroduction.

Between 2005 and 2007, DEC translocated 10 potoroos from the original colony at Two Peoples Bay to the 809 ha predator-free Bald Island, located off the south coast of Western Australia. The population appears to be thriving, with 49 individuals being recorded in 2010, several of which were carrying pouch young.  In 2010, a further nine potoroos were released into a specially built 308ha enclosure in Waychinicup National Park, 25km east of Albany. These new populations serve as insurance against extinction of the Two Peoples Bay population, and will significantly boost the chances of the species surviving in the long term.

A captive breeding facility was established adjacent to the wild population in 1994–1996, with six adults and three pouch young taken from the wild population. Few animals, however, have been successfully reared. Problems with captive propagation have not been resolved, and contributing factors may include illness, old age, immaturity, and as yet unspecified reasons. A major issue is that founder animals of the colony have died or are reaching reproductive senescence and the wild population is too small to continue withdrawing animals.

Research actions include studying the species’ ecology and biology, undertaking assisted reproduction techniques, regular monitoring of known populations plus surveys to search for additional populations.Further understanding the biology and ecology of Gilbert's potoroosResearch Project Partners

SCNRM (South Coast Natural Resource Management Inc)
previously known as SCRIPT (South Coast Regional Initiative Planning Team) Zoos South Australia Perth Zoo FAME (Foundation for Australia's Most Endangered Species Inc) Gilbert's Potoroo Action Group Inc Post Graduate students from Western Australian universities
Conservation Proposed
Most of the conservation recommendations made in the 2003-2008 Gilbert's Potoroo Recovery Plan are being implemented (see above), and these efforts should continue. Controlling the rate of Phytophthora infection in the habitat of this species is also important.
Links
References

Courtenay, J. and Friend, T. 2004. Gilbert’s Potoroo Recovery Plan. Wildlife Management Program No. 32. Government of Western Australia, Dept. Conservation and Land Management.

Friend, T. & Burbidge, A. 2008. Potorous gilbertii. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 15 November 2010.

Stead-Richardson, E. et al. 2009. Monitoring Reproduction in the Critically Endangered Marsupial, Gilbert’s potoroo (Potorous gilbertii): Preliminary Analysis of Faecal Oestradiol-17b, Cortisol and Progestagens. Endocrinology article in press.

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