Justification
Listed as Vulnerable because the few ongoing monitoring programs demonstrate decline in population size and/or area of occupancy that exceeds 30% over a three generation period (15-18 years), because it is likely to face ongoing decline due to legacy impacts of habitat fragmentation, recent increases in land clearing in the Queensland parts of the distribution, and because habitat quality continues to be affected by inappropriate fire regimes and/or logging. The causes of decline (fire, logging, habitat clearing and fragmentation and climate change) have not ceased and may not be reversible. For these reasons, the species meets the requirements for listing as Vulnerable under criteria A2bc+3bc+4bc.
Geographic Range Information
The Yellow-bellied Glider occurs in forest and woodlands in a distribution concentrated in coastal areas and adjacent ranges of eastern Australia. There are two major disjunct areas of distribution, separated by a gap of ~400 km: one in a restricted part of the Wet Tropics region of northeastern Queensland, and the other which covers a much larger area of southeastern Australia, from central Queensland in the north to southeastern South Australia in the south.
Animals from these two areas of distribution are genetically distinct (Brown et al. 2006). The isolated Wet Tropics population has been described recently as P. a. brevirostrum (Cooper et al. 2023). It is restricted to a narrow and discontinuous strip of tall eucalypt forest on the western margins of wet tropical rainforests between the Herbert River in the south and the Windsor Tableland in the north. The total linear extent of this distribution is about 260 km. DERM (2011) noted that there are three disjunct subpopulations within this distribution.
The distribution of the nominate subspecies extends from a northern limit around Mackay in central Queensland to include much of southeastern Queensland, eastern New South Wales and eastern Victoria, as well as restricted areas of western Victoria reaching just over the border into South Australia. Most occurrences are near the coast and on the eastern side of the Great Dividing Range, but the distribution extends to the western slopes of the Great Dividing Range in parts of Queensland and New South Wales. There are isolated inland subpopulation in the Blackdown and Carnarvon Ranges of central Queensland. Through its distribution, the Yellow-bellied Glider occurs patchily, reflecting habitat preferences and the effects of land clearing.
Population Information
There is no reliable estimate of population size of the Yellow-bellied Glider. Maxwell et al. (1996) considered it ‘uncommon throughout range’. It typically occurs at low densities (0.05-0.14 individuals/ha: Kavanagh 1984, Henry and Craig 1984, Craig 1985, Goldingay and Kavanagh 1991, Goldingay and Jackson 2004). Woinarski et al. (2014) suggest there are over 100,000 mature individuals of the Yellow-bellied Glider (south-eastern), but due to ongoing decline, and in particular the effects of the 2019-20 bushfires that affected large areas of the subspecies' distribution, the current population size is likely to be fewer than 100,000 mature individuals. Woinarski et al. (2014) estimate the population size of the Wet Tropics subspecies Petaurus australis brevirostrum at 5,500 mature individuals. Goldingay et al. (2023) estimated the population size in Richmond Range NP (156 km2) in north-eastern New South Wales to be 323-808 adults.
Some isolated subpopulations are small. Carthew (2004) estimated that there were (then) only six individuals present in South Australia, in a single 200 ha forest patch. Many subpopulations have been extirpated (e.g. Carthew 2004) and the key threats causing local declines are likely to continue.
Habitat and Ecology Information
The Yellow-bellied Glider occurs in eucalypt-dominated forests and woodlands. Habitat suitability is determined in part by floristics. The species shows a clear preference for forest types dominated by gum-barked and winter-flowering eucalypts and a diversity of tree species(Kavanagh 1987, Eyre and Smith 1997, Eyre 2004, Goldingay 2021). Also, it prefers forest stands that are sufficiently mature to provide trees suitable for shelter (i.e. that contain hollows) and foraging (Milledge et al. 1991, Incoll et al. 2001, Eyre and Goldingay 2003).
The Yellow-bellied Glider is social. Pairs or larger family groups (of varying age and sex composition) occupy an exclusive large home range of 30-65 ha (Henry and Craig 1984, Craig 1985, Goldingay 1992, Goldingay and Kavanagh 1993, Goldingay et al. 2021). Home ranges need to be large because foraging substrates are widely dispersed and are variable through space and time (Goldingay and Kavanagh 1993, Goldingay 2000). Microhabitat preferences of Yellow-bellied Gliders may change seasonally according to patterns of flowering, bark-shed and availability of other food resources (Kavanagh 1984).
Yellow-bellied Gliders feed on sap drawn from incisions in large trees, usually eucalypts (Wallis and Goldingay 2014). Incisions are made using enlarged lower incisor teeth, and consist of characteristic V-shaped cuts on the tree trunk. Often, certain individual trees are heavily used as feed trees, while other nearby trees of the same species may be unused (Goldingay 1991). The factors that determine which individual trees are used are not understood. As well as sap-feeding, Yellow-bellied Gliders feed on insects, spiders, eucalypt nectar and pollen, insect exudates, and manna (Carthew et al. 1999, Eyre and Goldingay 2003, Goldingay 2008). This species is a pollinator of the trees it takes nectar from (Goldingay 1990, Quin et al. 1996).
The species is nocturnal, feeding at night and sheltering by day in hollows found in large old trees (Goldingay et al. 2018). Large hollow-bearing trees are a critical habitat resource for the species.
The Yellow-bellied Glider is reliant on large areas of mature forest (Milledge et al. 1991, Eyre and Smith 1997, Lindenmayer et al. 1999a, Incoll et al. 2001, Eyre 2002, 2004, 2007, van der Ree et al. 2004, Eyre and Buck 2005, Lindenmeyer et al. 2024). In south-eastern Queensland, Eyre (2002) considered that forest fragments needed to be at least 320 km2in order to be occupied by Yellow-bellied Gliders, and more generally Goldingay and Possingham (1995) considered that forest areas needed to be 180-350 km2to retain viable populations. The species does not persist in smaller fragments now isolated by clearing or pine plantations (Lindenmayer et al. 1999b). Consequently, large areas of continuous forest are needed to maintain population viability.
The impacts of fragmentation are particularly pronounced because of this species’ apparent incapacity to traverse extensive tracts (i.e. longer than gliding distance) of cleared land. The Yellow-bellied Glider can forage in tall regrowth (Kavanagh 2004) and may tolerate moderate levels of logging disturbance, provided old trees are retained within riparian zones and key sap tree species are retained (Goldingay and Kavanagh 1993, Kavanagh 2004), although such tolerance may be somewhat site-specific and vary with landscape context and subsequent management (Milledge et al. 1991, Eyre and Smith 1997, Lindenmayer et al. 1999). Disturbance in forests of mountain ash (Eucalyptus regnans) or alpine ash (E. delegatensis) associated with clear-felling and severe fire can cause major and enduring changes in habitat structure and tree species composition, with loss of foraging habitat and some potential den trees (Lunney 1987, Kavanagh et al. 1995, Kavanagh and Bamkin 1995). Logging tends to reduce the proportion of large stems in a forest stand which reduces the availability of hollow-bearing trees (and den sites) and foraging substrate and food resources, including nectar, sap and invertebrates (Eyre and Smith 1997, Eyre 2002, 2004). Yellow-bellied Gliders are eliminated from clear-felled and intensively logged forests (Smith et al. 1994). Subpopulations of Yellow-bellied Gliders have declined or been extirpated from sites exposed to high intensity wildfire.
Females typically give birth to a single young annually (Goldingay 2008).
Threats Information
The main threats to the species are (i) habitat clearing and fragmentation; (ii) timber harvesting; (iii) severe and extensive wildfire; and (iv) increased temperatures and changes to rainfall due to climate change.
The Yellow-bellied Glider is sensitive to impacts of habitat clearing and fragmentation because it occupies large and exclusive home ranges, and is unable to cross areas of cleared land. It requires large tracts of continuous forest habitat to maintain population viability, and shows low persistence in small and isolated forest fragments. Barriers such as roads potentially limit gene flow and cause local loss of genetic diversity, but this may be mitigated by the installation of tall wooden poles along the road-side, allowing for more dispersal (Taylor and Rohweder 2020). Past clearance of forest vegetation, mainly for conversion to agriculture, has had a large impact on populations of the Yellow-bellied Glider, and it is likely that local populations remain vulnerable because of the legacy effects of past fragmentation.
Timber harvesting reduces the density of the large trees that are critical habitat resources for the Yellow-bellied Glider, because they provide hollows, are important as individual food trees, and maintain canopy connectivity while offering launching and landing points for gliding. Survey in several areas show that the Yellow-bellied glider prefers old-growth forest and may be absent from recently logged areas (Smith et al. 1994, TSSC 2023). In the central highlights of Victoria, recent declines of the species are associated with low availability of hollow-bearing trees, and young age of forest stands (Lindenmeyer et al. 2024).
Forest fires threaten the Yellow-bellied glider by causing direct mortality and by removing important habitat features, especially large hollow-bearing and sap-producing trees (Woinarski et al. 2014). The impacts of fire increase with fire severity and extent. The catastrophic fires of the summer of 2019/20 are estimated to have caused a short-term reduction of the population of the Yellow-bellied Glider (south-eastern) of 21%, rising to 25% over three generations (Legge et al. 2021). Goldingay et al. (2024) reported declines of 13-66% due to a single wildfire based on knowledge of occupied home ranges pre-wildfire. Because of climate change, fires of this severity and scale are becoming increasingly frequent in Australia and elsewhere; this trend is likely to continue.
Rising temperatures will increase the water requirements of arboreal marsupials and potentially cause water stress and hence sap production, especially in conjunction with increased variability of rainfall and consequent periods of drought. A study modelling the distribution of the Yellow-bellied Glider in south-east Queensland projected substantial contraction of core and marginal habitat for the species due to anticipated climate change, even under low warming scenarios (Handayani et al. 2019).
Use and Trade Information
Conservation Actions Information
This species is present in many protected areas. In state forests subject to harvesting, sap trees must be identified and preserved, but the effectiveness of this measure is uncertain (Goldingay 2008). Timber-harvesting and fire management should be aimed at maintaining tree-hollows and extensive areas of suitable forest.
The nominate subspecies is listed as Vulnerable, and the Wet Tropics subspecies as Endangered, and hence provided some protection, under Australian legislation and a Conservation Advice provides a general guide to management actions (DAWE 2022).
