Potorous gilbertii 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Diprotodontia Potoroidae

Scientific Name: Potorous gilbertii
Species Authority: (Gould, 1841)
Common Name(s):
English Gilbert's Potoroo
Potorous tridactylus ssp. gilbertii (Gould, 1841)
Taxonomic Notes: No subspecies are recognised. In the past, some authors considered Gilbert’s Potoroo to be a subspecies of the Long-nosed Potoroo Potorous tridactylus. Mitochondrial DNA sequencing has shown that it is a distinct species (Sinclair and Westerman 1997; Frankham et al. 2012) and more closely related to P. tridactylus than P. longipes.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered D ver 3.1
Year Published: 2016
Date Assessed: 2016-06-27
Assessor(s): Woinarski, J. & Burbidge, A.A.
Reviewer(s): Johnson, C.N. & Hawkins, C.
Contributor(s): Start, T., Friend, T. & Pacifici, M.
Gilbert’s Potoroo occurs naturally as a single, very small subpopulation on Mount Gardner in Two Peoples Bay Nature Reserve, Western Australia. It has been successfully introduced (assisted colonisation) to Bald Island Nature Reserve (8 km2) and is being reintroduced to a 3.8 km2 mainland island at Waychinicup National Park. The main factors that are the cause of the species being eligible for listing in the Critically Endangered category are its small population size and its precarious geographic distribution. In 2012 there was estimated to be 100 individuals (Woinarski et al. 2014) but it has approximately halved in 2015, mostly due to fires.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Gilbert’s Potoroos probably never had a large geographic range, as subfossil and modern data reveal a past distribution near the south coast of Western Australia from near Margaret River to near Albany. Three early collectors found it in the vicinity of King George Sound (Albany) between 1840 and 1879, but exact locations are unknown. John Gilbert, who collected specimens for John Gould, reported that he had not heard of it being found anywhere else but King George Sound (Gould 1863). Gilbert’s Potoroo was, for a long time, thought to be extinct, despite targeted searches (Kabay and Start 1976), until it was rediscovered on Mount Gardner, Two Peoples Bay Nature Reserve, in 1994 (Sinclair et al. 1996). In November 2015 wildfire caused the near loss of this population. It has been successfully introduced (assisted colonisation) in 2005-2007 to Bald Island Nature Reserve (8 km2).  This population was estimated to exceed 65 individuals in 2012 but is currently estimated to be around 40 individuals (DPaW pers comm. 2016), and has been reintroduced, in 2009, to a fenced mainland island at Waychinicup National Park (Bougher and Friend 2009). Despite regular supplements from Bald Island, this population has failed to thrive, and now comprises less than 20 individuals. A captive colony was maintained for 15 years but captive breeding was not successful with no offspring provided for translocations and all remaining captive animals were released into the Waychinicup fenced enclosure in 2010 (Woinarski et al. 2014).
Countries occurrence:
Australia (Western Australia)
Additional data:
Estimated area of occupancy (AOO) - km2:10Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:10
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Gilbert’s Potoroo was rediscovered on Mount Gardner within Two Peoples Bay Nature Reserve in 1994 after the implementation of a fox baiting program. Currently, there are an estimated 30-40 individuals in the Mount Gardner subpopulation and this appears to be the maximum that can be supported by the available habitat (Friend 2008b, 2009). Ten Gilbert’s Potoroos were translocated from the wild population on Mount Gardner to Bald Island in six separate releases between 2005–2007 (Friend 2009, Finlayson et al. 2010). Recent estimates suggest a current (2012) population on Bald Island of around 60 (T. Friend pers. comm.). In 2009, six Bald Island animals were removed in the first of a series of transfers, along with captive animals, to start a new semi-captive population in a 380 ha fenced area in Waychinicup National Park, in 2012 comprising more than 20 animals. In late 2007 (five years prior to this evaluation) there were c. 40-45 mature individuals, and the number may have exceeded 50 mature individuals of Gilbert’s Potoroo by the end of 2009 (T. Friend pers. comm.). However, recent data (2014) suggest that the species has declined at some sites.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:49Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:

Gilbert’s Potoroos inhabit dense, long-unburnt heathland. At Two Peoples Bay, the heaths they inhabit are about 1.5-2.5 m high and are dominated by Melaleuca striata and M. thymoides with a dense layer of sedges underneath. The area has not been burnt for more than 50 years (Courtenay and Friend 2004). In the past, local colonies were probably wiped out by fire, as the general area is fire prone, but would have moved back into regenerating vegetation from nearby colonies (Friend 2009).

The diet consists almost entirely of fungi. A study of dietary composition based on faecal analysis (Nguyen et al. 2004) found that fungal material made up more than 90% of the scat contents, the remainder comprising sand and root material that had apparently been ingested incidentally, as well as invertebrates and occasionally seeds from fleshy fruits. While 44 species of fungi were consumed in total, five species were found to be consumed by over 60% of animals in all seasons of the year. Gilbert’s Potoroo is one of the most fungi dependent mammals in the world.

Trapping and radio-tracking has 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 (Courtenay and Friend 2004).
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):3-4
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): Predation by introduced red foxes and feral cats are the major threats. Fire is also a major threat at Two Peoples Bay as the subpopulation there is highly restricted and dependent on old vegetation. A large fire would eliminate most habitat and exacerbate predation by feral cats and red foxes. Bald Island is thought not to have burnt for hundreds of years. 
In November 2015 a bushfire burnt through the Mt Gardner headland of Two Peoples Bay Nature Reserve, near Albany, Western Australia and severely impacted the habitat of the original wild population of Gilbert’s Potoroo. In January 2016 this species was identified as one of the 20 mammals within the Australian Government’s Threatened Species Strategy for priority conservation. This conservation advice has been updated in consultation with the Western Australia government to reflect the current status of this species and any proposed changes to conservation actions (Woinarski et al. 2014).

Conservation Actions [top]

Conservation Actions:

Recovery is guided by the Gilbert’s Potoroo Recovery Plan (Courtenay and Friend 2004), which superseded an interim recovery plan prepared within a few weeks of the species' rediscovery (Start and Burbidge 1995). Actions are:

·         Protect the existing wild population and habitat.

·         Increase understanding of ecology and population biology of Gilbert’s Potoroo to underpin management strategies.

·         Search for new populations of Gilbert’s Potoroo outside Two Peoples Bay.

·         Establish a self-sustaining captive breeding colony of Gilbert’s Potoroos for security, breeding, research and reintroduction.

·         Develop techniques to enhance the reproductive potential of Gilbert’s Potoroo.

·         Enhance breeding capacity of Gilbert’s Potoroo.

·         Extend the range of Gilbert’s Potoroo through translocation of animals to suitable habitat outside Two Peoples Bay. This has been successful by translocation to Bald Island and the establishment of the subpopulation within a fenced area on Mt Manypeaks.

·         Secure ongoing funding for the implementation of the Recovery Actions.

All actions are completed or are ongoing, except captive breeding: a captive colony was maintained for 15 years but captive breeding has not been successful enough to provide surplus animals for translocations and all remaining captive animals were released into a 380 ha fenced ‘mainland island’ in 2010. Cross fostering was carried out over on an experimental basis with limited success (Taggart et al. 2010). Considerable research has been conducted into the biology, ecology and reproduction of Gilbert’s Potoroo and is ongoing. Extensive searches using hair-trapping have been carried out in suitable habitat along the coast from Two Peoples Bay to Northcliffe and in the Margaret River area. Less targeted surveys have been carried out to the east of Albany, especially in the Fitzgerald River National Park, but no new populations have been discovered. The majority of ongoing funding has been provided by the Western Australian Department of Environment and Conservation and the Australian Government through the Natural Heritage Trust, with contributions from the Gilbert’s Potoroo Action Group, WWF-Australia Threatened Species Network, and the Foundation for Australia’s Most Endangered Species Ltd (FAME).

Following rediscovery of Gilbert’s Potoroo, there was extensive research into the species’ biology and ecology (e.g. Sinclair et al. 1996, 2000, 2002; Sinclair and Westerman 1997; Nguyen et al. 2004; Cochrane et al. 2005; Vaughan et al. 2007; Austin et al. 2009; Friend 2009; Bougher and Friend 2009; Lee et al. 2009; Taggart et al. 2010; Stead-Richardson et al. 2010) and a captive breeding facility was constructed in the hope that captive-bred potoroos could be reintroduced to other conservation reserves. Captive breeding, however, has proved to be difficult (Friend 2009), even with cross-fostering (Taggart et al. 2010), and the decision was taken to introduce wild potoroos from Two Peoples Bay to Bald Island Nature Reserve, the only island in the region that had suitable habitat. Monitoring of the Bald Island subpopulation shows that it has expanded to occupy most available habitat.

The Western Australian Department of Parks and Wildlife manages Two Peoples Bay Nature Reserve, Bald Island Nature Reserve and Waychinicup National Park. Management of Two Peoples Bay is conducted in accordance with a management plan (Orr et al. 1995, amended in 2004). Management includes aerial and ground baiting to control the Red Fox, trapping to control feral Cats, fire management including exclusion of prescribed fire from Mt Gardner (which also protects threatened bird taxa including the Noisy Scrub-bird Atrichornis clamosus), and monitoring of Gilbert’s Potoroo and other threatened species. In 2009, a 380 ha area within Waychinicup National Park was fenced to exclude foxes and feral Cats. Potoroos were transferred to this mainland island from Bald Island and Mount Gardner between 2010 and 2012 (Friend et al. 2012). Management of the enclosure involves regular inspection and maintenance of the fence, fire management, monitoring for sign of foxes and cats and a program of fox baiting inside and outside the enclosure.

Citation: Woinarski, J. & Burbidge, A.A. 2016. Potorous gilbertii. The IUCN Red List of Threatened Species 2016: e.T18107A21960726. . Downloaded on 22 January 2017.
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