Petaurus Australis Research Articles

Variable persistence of an iconic arboreal mammal through the Black Summer wildfires

Wildfires are predicted to increase in frequency and severity with climate change but detailed understanding of their influence on forest wildlife is lacking for many species. Wildfires vary in their extent and severity among landscapes, limiting generalisations about impacts from a single wildfire. We investigated post-wildfire persistence in the threatened exudivorous yellow-bellied glider (Petaurus australis) in south-eastern Australia. The widespread occurrence of wildfires in the ‘Black Summer’ of 2019–20 enabled populations in three landscapes (90–160 km apart) to be studied. This species has a slow life history (one young per year and >1 year to mature) so post-fire recovery is predicted to be slow. We conducted repeat surveys over 3 years post-fire in each landscape at 25–29 sites that were occupied pre-wildfire. All survey sites were burnt in two landscapes but only 40 % were burnt in the third. We estimated declines in occupancy of 13 %, 40 % and 66 % in burnt forest. The factors driving the variation in decline appear to be a combination of fire severity and the abundance of very large (≥80 cm) hollow (i.e. cavity) -bearing trees that serve as den sites. The implications of this study are that the impacts of wildfires on populations of tree-hollow dependent species can be expected to vary in different landscapes as a consequence of fire severity, rainfall deficit and logging history. Our study suggests the importance of ensuring populations are conserved across a wide geographic gradient, and the value of very large hollow-bearing trees rather than simply the number of any hollow-bearing trees.

A pilot study to encode calls from the northern yellow-bellied glider

As one of the most vocal marsupials in Australia, conservation of the yellow-bellied glider (Petaurus australis brevirostrum) (YBG) could benefit from the extraction of more information from their calls during acoustic monitoring. This pilot study investigates the variability of syllable components of full calls and identifies acoustic parameters that underlie variability in recorded calls from wild YBGs in North Queensland, Australia. Full calls with three syllables and with two syllables were distinguished. Using batch correlations and principal component analyses (PCAs), it was found that syllable two and syllable three show high variability in their duration and that maximum frequency is the strongest contributing sound parameter to the observed variability. However, because data collection was done in wild populations, the identity of call emitters remained unknown during call analyses, demanding further studies. Further subdivision of calls, and investigation into further acoustic parameters, could aid in decoding sexual, seasonal and individual-based meanings of calls.

Drought-induced population decline in an exudivorous mammal and its relevance to forest management

Droughts are predicted to increase in frequency and severity with climate change, so understanding their influence on species is fundamental to future conservation actions. Knowledge of whether species are at risk of decline due to drought may change the direction of how species and forests are managed. Exudate feeding non-flying mammals may be particularly sensitive to drought conditions, due to negative effects on exudates, but few studies of adequate length have been conducted. We investigated whether occupancy and abundance of a threatened exudivorous mammal, the yellow-bellied glider (Petaurus australis), were influenced by an extreme drought in eastern Australia. We conducted repeat surveys over eight years, which coincided with a drought that peaked in year 6, and was followed by two years of above average rainfall. Modelling suggested a slight decline in occupancy over the eight years (0.96–0.89). A marked decline in the probability of detection from pre-drought (0.72; 95 %CI: 0.65–0.79) to post-drought (0.30; 0.19–0.40), suggested a decline in abundance had occurred. Data on the maximum number of individuals detected per occupied site per year confirmed a decline in abundance. Counts of ≥ 3 individuals were recorded at 42% of occupied sites before the drought but at only 6% of occupied sites after the drought, equating to a 48% decline in abundance. These findings suggest that occupancy may be an unreliable measure of drought response in this species. Other exudivorous mammals may be sensitive to drought and require detailed study. Identifying drought refuges for these species should be added to existing forest management actions.

Food tree selection by an arboreal marsupial: Implications for timber harvest

ContextThe Yellow-bellied Glider (Petaurus australis) is a vulnerable arboreal Australian marsupial that is threatened by logging. Trees used for sap feeding (sap trees) are a critical habitat requirement of the species, yet no harvest retention policy exists in the southern part of its range in Victoria, Australia. Yellow-bellied Gliders are extremely selective in sap tree use with some trees used far more frequently than others. AimsWe aimed to determine the tree species used and identify characteristics influencing intra-species tree selection for sap feeding by Yellow-bellied Gliders in the Highlands - Southern Fall Bioregion of Victoria. MethodsSap trees were located at each of 12 sites. We measured nine characteristics related to photosynthetic capability, microsite, and habitat for sap trees and the nearest tree of the same species without Yellow-bellied Glider incisions (reference tree). For sap trees, we measured 11 incision-related variables. Permutational Multivariate Analysis of Variance was conducted to identify distinguishing characteristics of sap trees. Generalised Linear Mixed Modelling was used to determine the influence of tree characteristics on abundance of incisions on a tree. Key resultsFive of 24 tree and tall shrub species present across the 12 sites were used for sap feeding. All five species were Eucalyptus. Within the tree species used, Yellow-bellied Gliders selected for trees that were larger, had wider crowns and occupied dominant and co-dominant canopy positions. ConclusionsYellow-bellied Gliders are highly selective of trees used for sap feeding. Although primarily selecting larger more dominant trees for sap feeding, lack of clear identifying characteristics means that identifying and retaining preferred sap trees in logging coupes must rely on site surveys for incisions on trees.

Reassessment of the subspecific status of the Australian Wet Tropics yellow-bellied glider, Petaurus australis

The Wet Tropics (WT) population of the yellow-bellied glider Petaurus australis Shaw, 1791 in North Queensland is listed as Endangered at the state and national level, but its taxonomic classification is currently uncertain. Here we expand on previous genetic and morphological analyses of the WT population with additional samples and genetic loci to re-assess its subspecific status. Phylogenetic analyses of the mitochondrial NADH dehydrogenase subunit 4 (ND4) gene showed that the WT population formed a reciprocally monophyletic group relative to a group comprising P. australis from its remaining distribution in Australia. The genetic distinction of the WT population was further corroborated by analyses of the nuclear gene von Willebrand factor. Molecular clock analyses of combined ND2–ND4 data suggested that the WT population has been isolated from neighbouring populations in southern Queensland over multiple ice age cycles. Morphological analyses show that the WT gliders are smaller, with proportionally shortened faces, and have paler bellies compared to southern yellow-bellied gliders. We, therefore, propose that the WT population be recognised as a distinct subspecies which we herein describe. This taxonomic reassessment of P. australis has important implications for the ongoing conservation management of the WT population and yellow-bellied gliders throughout Australia.

Variation in sap feeding and tree testing by yellow-bellied gliders and the potential for population monitoring

Tree sap is important in the diet of the yellow-bellied glider (Petaurus australis). I investigated the use of 66 trees in sap feeding by gliders at 32 sites (equating to 32 glider groups) in eight surveys over 2 years in the Shoalhaven region of New South Wales to evaluate the potential to use such trees in population monitoring. I estimated the probability of detecting two different types of glider incision made on the sap trees within 0–3 months of a survey: one representing bouts of sap feeding and the other representing the testing of the suitability of these trees for sap feeding. The probability of detecting each type of incision varied by season, being lowest in autumn and highest in spring (feeding: 0.30 ± 0.03 (s.e.) to 0.51 ± 0.04; testing: 0.40 ± 0.04 to 0.63 ± 0.03). I also investigated whether detection of any new incision differed between individual sap trees at a site. The probability of detection per survey was equivalent (0.76 ± 0.03) between trees and between years. The incisions accumulate over a year, so scoring any incisions made since a previous annual survey will increase this probability. New incisions were detected in each of the two sample years at all sites indicating short-term stability in home range occupancy and demonstrating a useful method of population monitoring.

Long-term monitoring of an endangered population of Yellow-bellied Glider Petaurus australis on the Bago Plateau, New South Wales, and its response to wildfires and timber harvesting in a changing climate

ABSTRACT A population of Yellow-bellied Glider Petaurus australis on the Bago Plateau, on the NSW south-western slopes, was first surveyed across 126 sites in 1995 and this subsequently became the baseline for further population monitoring. A subset of 48 sites was resurveyed in 2010, and about one third of the sites (~40) were surveyed annually on a rotating panel between 2013–2019. Wildfire significantly impacted the Bago Plateau during 2020 and 51 sites were resurveyed post-fire in 2020/21. An occupancy modelling approach was used to estimate trends in occupancy between 1995 and 2020/21, including the influence of various covariates. Initial occupancy was positively associated with the extent of Montane Gums and mixed Wet Peppermint/Montane Gum forest types within a 450 m radius of the survey site. Supported models revealed that colonisation over time was positively associated with the density of hollow-bearing trees at a site, while extinction was positively associated with the extent of high severity wildfire at a site. Despite wide confidence intervals, the long-term occupancy trend showed a stable to slight increase between 1995 and 2019, but a ~26% reduction following wildfire. The increasing trend occurred despite a long-term rainfall deficit that was punctuated by occasional above average years during the survey period. There was no evidence that timber harvesting influenced occupancy by the gliders, although harvesting is predominantly focused within stands containing Alpine Ash Eucalyptus delegatensis, with monospecific stands generally avoided by the glider.

Molecular detection of two new putative species of gammaherpesvirus in petaurid possums.

A molecular survey of herpesviruses in Australian native mammals was conducted, spanning 260 individuals from 27 species. Among the herpesviruses detected, a putative new gammaherpesvirus species was detected in the yellow-bellied glider (Petaurus australis), and another in the critically endangered Leadbeater's possum (Gymnobelideus leadbeateri). In addition, the known host range of the putative species macropodid gammaherpesvirus 3 (MaHV-3) is herein extended to the western grey kangaroo (Macropus fuliginosus). These findings expand our understanding of herpesviruses in Australian mammals and may inform biosecurity protocols for captive and translocated populations.

Considerations in the protection of marsupial gliders and other mature-forest dependent fauna in areas of intensive logging in the tall forests of Victoria, Australia

Context The tall forests of Victoria, Australia, which are available for logging, are foreshadowed to be converted from mature forest to hostile environments for mature-forest dependent species by 2030. This has occurred within a 60-year time-frame since the advent of industrial-scale logging in the region. In this light, Protection Areas (PAs) of approximately 100 ha have been implemented to protect habitat with high density populations of Yellow-bellied Gliders (Petaurus australis) and Southern Greater Gliders (Petauroides volans). Aims and methods Ten considerations are provided to guide location and design of PAs, and to provide set asides and other forms of protection for mature-forest dependent species in the context of the temporal and spatial scale of logging activity. Key results Considerations are grouped into Overall approach (precautionary), Survey records and habitat attributes (occurrence, habitat, vegetation types), Size and shape considerations (edge and fragmentation effects); Management history (logging and fire), and Boundary considerations (context and conditions). In addition, set asides encompassing home ranges; and high levels of basal area retention, are also required in the remainder of planned logging coupes. Conclusions Addressing these considerations in PAs, in set asides and in retention will provide some protection for mature-forest dependent species, but will be insufficient without ecologically sustainable forest management at the coupe level, for the sustained yield of all habitat components of these forests. Implications The conservation of mature-forest dependent species in the context of an ongoing timber industry requires logging return times well beyond current expectations, resulting in a substantial reduction in resource commitment to industry.

Logging and wildfire limit the distribution of a vulnerable arboreal mammal

Habitat loss and degradation are two of the greatest threats to biodiversity conservation globally. In Australia, the incidence of wildfire and native forest logging contribute substantially to these processes and have been linked to reduced species diversity and abundance. Arboreal species such as the Yellow-bellied Glider (Petaurus australis), are thought to be susceptible to these disturbances due to their reliance on large patches of forest and hollow-bearing trees. We aimed to assess the impact of logging and wildfire on site occupancy by the Yellow-bellied Glider in Mountain Ash forests of the Central Highlands of Victoria. We deployed autonomous recording units for 14 nights at 70 sites and searched recordings for Yellow-bellied Glider vocalisations. Yellow-bellied Gliders were detected at 30% (N = 21) of sites. Site occupancy increased with an increasing proportion of the landscape (within 400 m of the recorder) that had not been logged within the last 100 years or burnt by wildfire within the last 10 years. Habitat disturbance caused by logging and fire therefore limit the site occupancy of Yellow-bellied Gliders and likely impact its conservation status. It is therefore critical that appropriate management of timber resources protects large patches of old-growth forest providing food resources and hollows, and the connectivity between large forest patches.

Passive acoustic monitoring for detecting the Yellow-bellied Glider, a highly vocal arboreal marsupial.

Passive acoustic monitoring (PAM) is increasingly being used for the survey of vocalising wildlife species that are otherwise cryptic and difficult to survey. Our study aimed to develop PAM guidelines for detecting the Yellow-bellied Glider, a highly vocal arboreal marsupial that occurs in native Eucalyptus forests in eastern and south-eastern Australia. To achieve this, we considered the influence of background noise, weather conditions, lunar illumination, time since sunset and season on the probability of detecting vocalisations. We deployed Autonomous Recording Units (ARUs) at 43 sites in the Central Highlands of Victoria during two periods: spring/summer (October 2018 to January 2019), and autumn/winter (May to August 2019). ARUs were programmed to record for 11 hours from sunset for 14 consecutive days during each period. Background noise resulted from inclement weather (wind and rain) and masked vocalisations in spectrograms of the recordings, thus having the greatest influence on detection probability. Vocalisations were most common in the four hours after sunset. Rainfall negatively influenced detection probability, especially during the autumn/winter sampling period. Detection of Yellow-bellied Gliders with PAM requires deploying ARUs programmed to record for four hours after sunset, for a minimum of six nights with minimal inclement weather (light or no wind or rain). The survey period should be extended to 12 nights when rain or wind are forecast. Because PAM is less labour intensive than active surveys (i.e., spotlighting and call playbacks with multiple observers and several nights’ survey per site), its use will facilitate broad-scale surveys for Yellow-bellied Gliders.

General or local habitat preferences? Unravelling geographically consistent patterns of habitat preference in gliding mammals

Central to the conservation of animal species is identifying factors that influence habitat preference. General factors that operate across a species’ geographic range are of particular importance because they allow management actions to be applied when resources are limited. Local factors may also be important but require detailed study to identify. Distinguishing general from local factors is therefore key to conservation planning. Occupancy modelling was used to investigate habitat preferences in one landscape in south-eastern Australia of the regionally threatened yellow-bellied glider (Petaurus australis) (naïve occupancy = 0.72) and the non-threatened sugar glider (Petaurus breviceps) (naïve occupancy = 0.84). Hypotheses were tested to determine whether preferences were of general or local relevance. The habitat model with the greatest support for the yellow-bellied glider (a negative relationship with dead tree abundance) was specific to this landscape, which might suggest a local factor. This was interpreted to reflect a negative response to fire and may be an unrecognised general factor. In contrast, the best supported model for the sugar glider (a positive relationship with increasing basal area of winter-flowering trees) represented a general factor. This study suggests there is utility in evaluating habitat factors for their general relevance but this approach relies on the availability of detailed studies across the geographic range for this approach to be effective.

Yellow-bellied gliders use glide poles to cross the Pacific Highway at Halfway Creek, north-east New South Wales

The installation of glide poles to enable gliding mammals to cross wide road corridors has become a common feature of highway upgrades in eastern Australia. While frequent use by small species has been well documented, records of use by large glider species are scant. During 15 months of camera monitoring of two glide poles in the median of the Pacific Highway at Halfway Creek, north-east New South Wales, yellow-bellied gliders (Petaurus australis) were detected on nine occasions. On three of these occasions, video footage captured glide launches across the northbound carriageway. Our study provides the first definitive evidence of repeated use of wooden glide poles by the yellow-bellied glider to cross a highway corridor. Glide poles, therefore, have the potential to restore functional connectivity for yellow-bellied gliders at locations where major roads bisect forest habitat.

Use of tall wooden poles by four species of gliding mammal provides further proof of concept for habitat restoration

Tall wooden poles (glide poles) and rope canopy-bridges are frequently installed along new highways in Australia to maintain population connectivity for gliding mammals. Knowledge of the use of these structures is rudimentary. We monitored two pairs of glide poles and a canopy-bridge over three years at Port Macquarie, New South Wales. The sugar glider (Petaurus breviceps) and the squirrel glider (Petaurus norfolcensis) were collectively detected on 12–18% of nights on the pole pairs compared with 1% on the rope-bridge. The feathertail glider (Acrobates frontalis) was detected on 3% of nights on the pole pairs compared with 0.2% on the rope-bridge. The yellow-bellied glider (Petaurus australis) was detected twice on one pole. Our results demonstrate that gliding mammals readily use glide poles. Further research is needed to resolve whether glide poles can mitigate the barrier effect of the road canopy gap.

Extensive range contraction predicted under climate warming for a gliding mammal in north-eastern Australia

We used MaxEnt to model the current distribution of the yellow-bellied glider (Petaurus australis) and to predict the likely shift in the species’ future distribution under climate-warming scenarios in the Wet Tropics (WT) Bioregion in north Queensland and in the South-eastern Queensland (SEQld) Bioregion, which encompasses south-eastern Queensland and north-eastern New South Wales. Bioclimatic layers were used to generate models from 57 independent records in the WT and 428 records in SEQld. The modelled distribution of core habitat under current climate showed a good fit to the data, encompassing 91% and 88% of the records in each area, respectively. Modelling of future warming scenarios suggests that large contractions in distribution could occur in both bioregions. In the WT, 98% of core habitat is predicted to be lost under low warming (1°C increase) and 100% under high warming (2−3°C increase) by 2070. In SEQld, 80% of core habitat is predicted to be lost under low warming and 90% under high warming by 2070. These results suggest that this species is highly vulnerable to climate warming and highlight the importance of focusing conservation efforts at the bioregional scale. There is also a need to identify potential thermal refuges and ensure habitat connectivity.

Characteristics of the den trees of the yellow-bellied glider in western Victoria

Effective management of tree-hollow-dependent wildlife is enhanced by detailed knowledge of the trees used for shelter and breeding. We describe the characteristics of 52 den trees and hollows (cavities) used by the yellow-bellied glider (Petaurus australis) in the south-west of its geographic range. We compared the following attributes of den trees to reference trees: tree height, diameter at breast height, hollow entrance height, hollow entrance diameter, cavity diameter, cavity depth, cavity roof height and cavity wall thickness. Dens and reference trees showed a highly significant multivariate difference (P<0.001), with these variables explaining 64% of the variance. Univariate analyses revealed that hollow entrance height was significantly different between den trees (9.0±0.5m) and reference trees (5.5±0.3m). While not significant, den trees tended to have narrower hollow entrances, deeper cavities and thinner walls than reference trees; cavities used by yellow-bellied gliders, on average, measured 36.8cm deep and 18.0cm in diameter, and had entrances 10.6cm in diameter. These observations should assist forest management for this species.

Integrated species distribution models: combining presence‐background data and site‐occupancy data with imperfect detection

Summary Two main sources of data for species distribution models (SDMs) are site‐occupancy (SO) data from planned surveys, and presence‐background (PB) data from opportunistic surveys and other sources. SO surveys give high quality data about presences and absences of the species in a particular area. However, due to their high cost, they often cover a smaller area relative to PB data, and are usually not representative of the geographic range of a species. In contrast, PB data is plentiful, covers a larger area, but is less reliable due to the lack of information on species absences, and is usually characterised by biased sampling. Here we present a new approach for species distribution modelling that integrates these two data types. We have used an inhomogeneous Poisson point process as the basis for constructing an integrated SDM that fits both PB and SO data simultaneously. It is the first implementation of an Integrated SO–PB Model which uses repeated survey occupancy data and also incorporates detection probability. The Integrated Model's performance was evaluated, using simulated data and compared to approaches using PB or SO data alone. It was found to be superior, improving the predictions of species spatial distributions, even when SO data is sparse and collected in a limited area. The Integrated Model was also found effective when environmental covariates were significantly correlated. Our method was demonstrated with real SO and PB data for the Yellow‐bellied glider (Petaurus australis) in south‐eastern Australia, with the predictive performance of the Integrated Model again found to be superior. PB models are known to produce biased estimates of species occupancy or abundance. The small sample size of SO datasets often results in poor out‐of‐sample predictions. Integrated models combine data from these two sources, providing superior predictions of species abundance compared to using either data source alone. Unlike conventional SDMs which have restrictive scale‐dependence in their predictions, our Integrated Model is based on a point process model and has no such scale‐dependency. It may be used for predictions of abundance at any spatial‐scale while still maintaining the underlying relationship between abundance and area.

Selection of sap feed trees by yellow-bellied gliders (Petaurus australis) in north-eastern Queensland, Australia – implications for site-specific habitat management

Knowledge of site-specific ecological factors affecting a species’ resource selection is essential to assist in habitat management for a species’ conservation, particularly for species with narrow resource width. This study aimed to assess whether microhabitat variables affect the selection of Eucalyptus resinifera sap feed trees by yellow-bellied gliders (Petaurus australis) in north-eastern Australia. Microhabitat variables were measured in a simplified way around glider-selected and -non-selected Eucalyptus resinifera trees. Canopy cover and percentage of burnt trunk below breast height were identified as influential on feed tree selection, with feed trees showing a higher percentage of burnt trunk and a lower surrounding canopy cover. While the direct effect of fire on a potential feed tree remains to be clarified, fire may affect the structural composition of vegetation leading to lower surrounding canopy cover around potential feed trees. Thus, any forest management, such as logging and grazing should be practiced with great caution since they affect structural features of the vegetation that may contribute to the selection of feed trees by this species and may also affect its alternative food resources.

Compact development minimizes the impacts of urban growth on native mammals

Summary Unprecedented global human population growth and rapid urbanization of rural and natural lands highlight the urgent need to integrate biodiversity conservation into planning for urban growth. A challenging question for applied ecologists to answer is: What pattern of urban growth meets future housing demand whilst minimizing impacts on biodiversity? We quantified the consequences for mammals of meeting future housing demand under different patterns of compact and dispersed urban growth in an urbanizing forested landscape in south‐eastern Australia. Using empirical data, we predicted impacts on mammals of urban growth scenarios that varied in housing density (compact versus dispersed) and location of development for four target numbers of new dwellings. We predicted that compact developments (i.e. high‐density housing) reduced up to 6% of the area of occupancy or abundance of five of the six mammal species examined. In contrast, dispersed developments (i.e. low‐density housing) led to increased mammal abundance overall, although results varied between species: as dwellings increased, the abundance or occurrence of two species increased (up to ∼100%), one species showed no change, and three species declined (up to ∼39%). Two ground‐dwelling mammal species (Antechinus stuartii and Rattus fuscipes) and a tree‐dwelling species (Petaurus australis) were predicted to decline considerably under dispersed rather than compact development. The strongest negative effect of dispersed development was for Petaurus australis (a species more abundant in forested interiors) which exhibited up to a 39% reduction in abundance due to forest loss and an extended negative edge effect from urban settlements into adjacent forests. Synthesis and applications. Our findings demonstrate that, when aiming to meet demand for housing, any form of compact development (i.e. high‐density housing) has fewer detrimental impacts on forest‐dwelling mammals than dispersed development (i.e. low‐density housing). This is because compact development concentrates the negative effects of housing into a small area whilst at the same time preserving large expanses of forests and the fauna they sustain. Landscape planning and urban growth policies must consider the trade‐off between the intensity of the threat and area of sprawl when aiming to reduce urbanization impacts.

Population monitoring of a threatened gliding mammal in subtropical Australia

Population monitoring is fundamental to the conservation of threatened species. This study aimed to develop an effective approach for long-term monitoring of the yellow-bellied glider (Petaurus australis) in north-east New South Wales. We conducted repeat surveys to account for imperfect detection and used counts in abundance modelling to produce indices of abundance. We used simulations to explore refinements to our study design. Surveys over three consecutive years produced 195 detections with >95% of detections by call. The probability of detection varied across years and survey occasions, ranging from 0.22 to 0.71. Abundance estimates were remarkably constant across years, ranging from 2.3 ± 0.5 to 2.4 ± 0.6 individuals per site. Occupancy estimates were also constant across years (0.90–0.91). Simulations were run to investigate the influence of the number of surveys (2 or 3) and the number of survey sites (20, 40 or 50) on the probability of occupancy. The design that reduced bias and provided an adequate improvement to precision was that of three visits to 40 survey sites. This design should be adequate to detect a decline in population abundance. Further studies of this kind are needed to better understand the population dynamics of this species.