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Pseudocheirus occidentalis 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Diprotodontia Pseudocheiridae

Scientific Name: Pseudocheirus occidentalis (Thomas, 1888)
Common Name(s):
English Western Ringtail Possum, Ngwayir, Western Ringtail
Taxonomic Notes: Pseudocheirus occidentalis has been synonymised with the Common Ringtail Possum P. peregrinus of eastern Australia by some authors, (e.g. Ride 1970, Groves 2005), or proposed as a subspecies of P. peregrinus. However, its distinctiveness is widely accepted, despite no published analyses of comparative morphology or molecular profiles (Woinarski et al. 2014)

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2bce+3bce+4bce ver 3.1
Year Published: 2017
Date Assessed: 2014-03-09
Assessor(s): Burbidge, A.A. & Zichy-Woinarski, J.
Reviewer(s): Hawkins, C.
Contributor(s): How, R., Jones, B., Morris, K., Start, T. & Wayne, A.
Justification:

The Western Ringtail Possum has an area of occupancy of <500 km², small and severely fragmented subpopulations, and is continuing to decline, being threatened particularly by a drying climate, urban development, inappropriate fire regimes, and predation by Red Fox (Vulpes vulpes) and feral cat (Felis catus). The subpopulation in the Upper Warren (Perup) was the largest prior to 2002 and underwent a severe decline of >95% (probably >99%) between 1998 and 2009. Remaining fragmented subpopulations in coastal habitats are also declining rapidly, equating to a population decline of >80% in the past 10 years. With rainfall in the south-west of Western Australia predicted to decline further and continuing urban coastal development, there is a projected continuing decline of >80% within the next 10 years.

Previously published Red List assessments:

Geographic Range [top]

Range Description:The extent of occurrence of Western Ringtail Possums has contracted in the past and severely contracted in the recent past. Formerly it was patchily distributed across much of south-western Western Australia from 120 km south-east of Geraldton (where it is known from surface cave deposits) to the southern edge of the Nullarbor Plain (where it is also known from surface cave deposits), with the most inland recent records being from Tutanning Nature Reserve east of Pingelly (Shortridge 1909; Sampson 1971; Christensen et al. 1985; How et al. 1987; Baynes 1987; Jones et al. 1994a,b; Jones and Hillcox 1995; Burbidge and de Tores 1998).

By ca 1980, about 80% of the original range was no longer occupied (Jones 2004). It persisted in the coastal strip between Bunbury and Albany (with the range extending inland in riparian habitat between the Collie and Blackwood Rivers), and in the Upper Warren region (Perup Nature Reserve, Greater Kingston National Park and adjacent State forest: Burbidge and de Tores 1998, Wayne et al. 2006). There are a few post-2000 Western Ringtail Possum records across some inland areas in south-western Australia from Yornup in the north to Northcliffe in the south, near Vasse Highway, near Carey forest block in the west and Lake Muir in the east (B. Jones pers. comm).

Currently, it occurs patchily in coastal areas from near Bunbury to the Leeuwin-Naturaliste National Park (with a small isolated translocated subpopulation further north near Dawesville) and near Albany (B. Jones pers. comm). Most of these fragmented habitat remnants are on private land. The largest recent inland subpopulation in the Upper Warren had declined to near extirpation by the mid- to late-2000s (Wayne et al. 2012), so there are now only two subpopulations.

It has been reintroduced to Lane-Poole Conservation Park near Dwellingup, Yalgorup National Park south of Mandurah and Leschenault Conservation Park near Bunbury. However, apart from some Yalgorup translocated animals establishing away from the release site near Dawesville, these reintroductions have failed due to poor-quality food resulting from a drying climate (B. Jones pers. comm.) and to feral cat predation (K. Morris pers. comm). There is a small subpopulation of <50 mature individuals (and therefore not included in this evaluation) in the Karakamia mainland island (Australian Wildlife Conservancy), near Perth.

There are five subpopulations: 'Southern Swan Coastal Plain', 'Cape to Cape' (Cape Naturaliste to Cape Leeuwin), 'Other Forest Rivers', 'Upper Warren' and 'Around Albany'.
Countries occurrence:
Native:
Australia (Western Australia)
Additional data:
Estimated area of occupancy (AOO) - km2:300-500Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:40000
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:How et al. (1987) found that subpopulations between Busselton and Albany were small and rapidly diminishing. In the Upper Warren area, Western Ringtail Possums have declined severely in abundance (>95%, probably >99%) between 1998 and 2009 (Wayne et al. 2011, 2012) from an inferred pre-decline abundance of >10,000 individuals (A. Wayne pers comm). Jones et al. (2007) found high-density remnant subpopulations varying between <2 and 20 adults/ha in the Siesta-Kealy area west of Busselton, and Harewood (2009) found densities of ca 13 animals/ha in Busselton urban bushland reserves in 2008 and 2009; however, these high densities are exceptional—many remnant areas now harbour few animals. Scat scores at Ludlow National Park and nearby sites revealed a 30-55% site decline between 2002 and 2012 (B. Jones pers. comm). The results of surveys carried out by consultants for developers are generally unavailable; however, anecdotal and observational evidence indicates that other remnant subpopulations have recently undergone significant decline (B. Jones pers. comm). The major cause of the decline is thought to be climate change (drying and warming) leading to declining food quality: Western Ringtail Possums require relatively high quality food to recruit successfully due to their specialized digestive system. Other implicated factors include continuing habitat loss and fragmentation due to urban development, and predation by introduced Red Foxes and feral cats.

Recent (2015) estimates by Dr B. Jones for each of the five subpopulations are:
  • Southern Swan:  2,000
  • Cape to Cape:  500
  • Other Forest Rivers:  300
  • Upper Warren:  100
  • Around Albany:  500
This implies a probable 2015 total of about 3,400 adult Western Ringtail Possums.

The most recent estimate of numbers at Karakamia, made in 2010, was 38 animals, and spotlighting since then suggests a stable subpopulation (S. Legge pers. comm).

The Upper Warren subpopulation was estimated to be at least 11,000 mature individuals in 2006. Numbers in other regional areas were also significantly higher in 2006, with a total estimate of the population in 2006 being at least 18,000. Thus, available information strongly implies a population size reduction of >80% over the past 10 years. Because rainfall is projected to decline further in south-western Australia, and habitat destruction is likely to continue, this reduction is expected to continue.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:3400Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:Yes
No. of subpopulations:5Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:YesAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:The Western Ringtail Possum is an arboreal marsupial with a maximum body weight of 1,330 g for both sexes (Wayne et al. 2005a). It formerly occurred in a variety of vegetation types including coastal Peppermint (Agonis flexuosa) forests and woodlands and Peppermint / Tuart (Eucalyptus gomphocephala) associations, eucalypt associations of Jarrah (E. marginata) / Marri (Corymbia calophylla) / Wandoo (E. wandoo) (Christensen et al. 1985), Wandoo / Casuarina (Allocasuarina huegeliana) woodland in the wheatbelt, and presumably eucalypt woodland, mallee and mallee heath from the Hampton Tableland (Baynes 1987) and other areas. It is now almost exclusively restricted to coastal and near coastal Peppermint woodland between the Australind - Eaton area and Waychinicup National Park (Burbidge and de Tores 1998). The Upper Warren area had the only known sites where Western Ringtail Possums recently persisted in significant numbers in the absence of Peppermint.

In coastal Peppermint habitat, Western Ringtail Possums build dreys as nesting/resting sites and uses tree hollows where available (e.g., Tuart and Marri). Where protection from introduced predators is provided, a wide range of nest sites on or near the ground has been recorded, including low shrub thickets (e.g., Basket Bush (Spyridium globulosum), Orange Wattle (Acacia saligna), Summer-scented Wattle (A. rostellifera)), sedges and rushes (ringtails have been commonly recorded nesting on the ground under sword sedge (Lepidosperma gladiatum) (How et al. 1984, Jones et al. 1994a). In the absence of predator control and in the absence of Peppermint or other nesting/drey material, or where fire is frequent, tree hollows and hollow logs are used almost exclusively, although urban animals will use roof spaces and other shelter. At translocation sites in the Jarrah forest near Dwellingup, where foxes are controlled, 20% of over 400 recorded day rest locations were at or below 1.5 m in height. These sites included hollow logs on the ground, fallen branches and debris on the ground, coppicing jarrah stumps, in and under Grass Tree (Xanthorrhoea sp.) leaf ‘skirts’ and in Water Bush (Bossiaea sp.) and Karri Hazel (Trymalium sp.) In Jarrah forest near Manjimup, where foxes are also controlled, up to 70% of diurnal refuges were sites other than tree hollows, including the skirts of grass trees (Xanthorrhoea sp.), stump hollows and hollow logs (Burbidge and de Tores 1998, Wayne et al. 2000).

The diet of the Western Ringtail Possum is variable. When available, Peppermint leaves form the majority of the diet. In their absence, the dominant myrtaceous species are preferred (Jones et al. 1994b). In urban areas (e.g., Bunbury and Busselton), they are known to feed on a variety of garden species, including rose bush leaves and flowers and a variety of fruits. The digestive system reflects adaptation to myrtaceous and other foliage of low nutritional value. Western Ringtail Possums are caecum fermenters having a large caecum where fine digestive material is retained. Larger, coarse, less nutritious material is passed more rapidly. Ringtail Possums are also caecotrophic (i.e., during the day they ingest softer, finer faecal material to assist in returning bacteria to the caecum to aid digestion: Hume and Sakaguchi (1993), Hume et al. (1994)). Successful recruitment depends on seasonal availability of high-quality foliage. When food quality is poor, the sex ratio of young is biased towards males, and recruitment may fail (B. Jones pers. comm). Wayne (2005) reported that 84% of monitored deaths (mostly linked to predation) occurred between April and September, when both male and female body condition was significantly lower than October-March.

Wayne et al. (2006) investigated associations between the relative abundance of the Western Ringtail Possum and anthropogenic disturbances at local and landscape scales within the publicly-managed Jarrah forests of south-western Australia. Logging, fire, fox control and forest fragmentation were investigated in relation to the relative abundance of ringtails at 90 sites within an area of 285,000 ha of the Upper Warren east of Manjimup; the location of the last remaining substantial population of the Western Ringtail Possum in jarrah forest. Overall, abundance was greatest in areas with limited anthropogenic disturbance. At the local scale, abundance was negatively associated with greater fire intensity. At the landscape scale, it was positively associated with fox control and negatively associated with forest fragmentation and distance from non-remnant vegetation (i.e., agriculture and tree plantations). Abundance was also greatest in predominantly unlogged landscapes and in forests that had been regrowing for an average of 40 years since the landscape was most recently logged; in other words, where logging was historically least intense.

Western Ringtail Possums are often killed in moderate or high intensity fires (Inions 1985) and by logging (Morris et al. 2000). Both impacts also expose survivors to elevated predation. Where most resident possums use predominantly low shelter sites, or dreys in the mid-storey, even low intensity fires can severely reduce numbers. Most resident subpopulations appear to require some substantial or dominant proportion of their local habitat to have remained largely unburned and unlogged for periods of at least 2-4 decades (Wayne 2008, Jones et al. 2007). By 2012, it was clear that drey-using fragmented subpopulations (in habitat with only rare, small fire events) were more resilient and persistent than subpopulations in habitat subject to broad-scale fire effects (wildfires or low-intensity prescribed fires).

Young have been recorded as being born throughout the year, with peaks in April to July and September to November (Jones et al. 1994b, Wayne et al. 2005a), but the breeding season can vary. Sexual maturity is reached at about one year. Litter size is usually one, with litters of two being rare, unlike the Common Ringtail Possum (P. peregrinus). Sex ratios can vary, depending on food quality: females predominate when food quality is high, males when it is low. Longevity is unknown. Life spans of P. peregrinus to eight years have been recorded (Jones et al. 1990) and longevity in captivity for that species is up to 10 years (AnAge 2012). Available information suggests that most Western Ringtail Possums do not survive in the wild beyond 3-6 years. Generation length for the Western Ringtail Possum is here assumed to be ca 3 years.
Systems:Terrestrial
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):3
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s):

Current threats are:

  1. The drying climate, affecting the nutritional quality of food and hence survival and recruitment. Rainfall has declined and continues to decline throughout the south west of Australia. T2014 and 2015 have been the, or close to the, driest on record near Albany. Albany mean rainfall (1877 to 2014): 929 mm; 2014: 638 (no data from December, mean is 30 mm, if 30 mm added = 668 mm); 2015: 621 mm (lowest on record). Busselton mean (1877 to 2014): 813.6 mm; 2014: 591 mm; 2015: 568 mm. Western Ringtail Possums ‘are among the species most likely to be impacted by predicted climate change in the south-west because they have very specific habitat and dietary requirements, have a poor ability to migrate and have lost large areas of habitat. In addition they are sensitive to drought-induced stress. Over the past 30 years there has been an approximate 20 per cent decline in rainfall in the south-west of WA, with more reductions in rainfall and increased temperatures predicted due to global climate change (Timbal 2004). These changes could result in further contraction of the species to the most fertile and mesic remnants of their extant range (Wayne 2005, Jones and Francesconi 2007)’ (Recovery Plan p. 10). Almost all remaining occurrences are associated with older-growth Peppermint, but few stands now seem to provide suitable nutrition for the species to survive and recruit
  2. Increasing temperature. ‘Western Ringtail Possums are known to be susceptible to heat stress and can easily overheat at temperatures of 35°C (Yin 2006). Western Ringtail Possums have been observed to use evaporative cooling in hot weather by applying saliva to the forelimbs or panting (Jones et al. 1994b). Jones et al. (1994b) observed that in areas where dreys were used, Western Ringtail Possums went to the ground over several hot days. Western Ringtail Possums are the smallest of the specialist marsupial folivores indicating that they live close to the ecological and physiological limits of viability (B. Jones pers. comm. 2002)’ (Recovery Plan pp. 6-7). As well, increasing temperatures exacerbate soil moisture reduction and further affect the nutritional quality of food.
  3. Land clearing. Land clearing for urban development remains a threat in the Busselton – Augusta near coastal strip and near Albany. Land clearing continues despite application of the EPBC Act guidelines that aim to assist in determining whether a proposed action is likely to have a significant impact on the Western Ringtail Possum on the southern Swan Coastal Plain. Most remaining habitat is on private land; thus the major land management is via planning controls, not via biodiversity legislation.
  4. Feral predators. Translocation experiments in the past and other data demonstrate that Red Foxes and feral Cats are major threats, especially where the canopy becomes more open due to ‘parkland clearing’ and after fire. Native predators also impact the species.
  5. Fire. Fire reduces food availability and opens up the canopy causing ringtails to spend more time on the ground where they can be predated by foxes and cats.
  6. Tree decline and insect outbreaks. Coastal Peppermint decline, gum leaf skeletoniser and Phytophthora dieback in Jarrah, Tuart decline and other tree declines have resulted in extensive but mainly localised reductions in food and habitat quality.
  7. Competition for tree hollows. Increased numbers of Brushtail Possums where fox baiting occurs leads to competition for hollows: brushtails are more aggressive and will evict ringtails. Hollow loss is also caused by logging and feral bees.
  8. Logging. Western Ringtail Possums are more abundant in unlogged forest or where logging has been least intense; logging leads to local mortality including via increased feral Cat predation. However, current WRP distribution does not now significantly overlap areas to be logged to a significant degree.
  9. Domestic dogs. ‘In urban environments predation or injury by domestic dogs can be frequent (de Tores et al. 1998). High levels of dog ownership within the City of Busselton create dog densities at four to eight times greater per hectare than the average fox density in the south-west forests (K. Williams pers. comm. 2006)’ (Recovery Plan, p.8). Ravens are a threat in urban areas where their numbers have increased.
  10. A plausible future threat is myrtle rust, which significantly affects peppermint (Agonis flexuosa), in eastern Australia where it is planted horticulturally, noting that peppermint is now the main habitat and food tree for WRPs.

Note that some threats are synergistic.

Conservation Actions [top]

Conservation Actions: Recovery goals, objectives, criteria for success and failure, and recovery actions are described in the Recovery Plan (Department of Parks and Wildlife 2014); however, this was drafted when the species was listed as Vulnerable.

The Recovery Plan includes >30 actions. The most urgent ones are:

Monitoring. It is clear that there is insufficient monitoring, especially noting the short-term crash that happened at the Upper Warren where the subpopulation went from >10 000 (probably many tens of thousands) to near zero in about 10 years, and average species’ longevity of c. 3 years. Of particular concern is declining rainfall and increasing temperatures and resulting effects on survival and recruitment, not only in the Bunbury to Augusta area, but also near Albany where there has been a series of dry years and severe, lightning-caused fires in the conservation estate.

Research into effects of drying climate, nutritional status of food and how it relates to survival and recruitment. This should include research into the effects of rainfall and artificial watering on the nutritional quality of food and hence recruitment.

Predation. Conduct experiments with Eradicat (registered feral cat bait) in key Western Ringtail Possum habitat and measure prey response.

Captive breeding. If the species continues to decline at rates seen in the past, captive breeding may be needed at some future time. A pilot study to develop husbandry techniques is indicated.


Citation: Burbidge, A.A. & Zichy-Woinarski, J. 2017. Pseudocheirus occidentalis. The IUCN Red List of Threatened Species 2017: e.T18492A21963100. . Downloaded on 12 December 2017.
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