Petaurus Norfolcensis Research Articles

Reducing nest box entrance diameter impacts mammal occupancy

Tree hollows are an important resource for cavity‐nesting birdlife. When large, old trees are removed from a landscape, nest boxes are often installed as part of restoration efforts to replace lost natural cavities. If nest boxes are to be successful conservation tools, non‐target species, particularly competitive and predatory species, need to be prevented from entering nest boxes. Several different modifications to nest boxes aimed at excluding non‐target species have been trialed in previous studies. We tested the effectiveness of reducing the entrance diameter of nest boxes to exclude non‐target species in Southeast Queensland, Australia. We used restrictor plates to reduce the entrance diameter of nest boxes from 90 to 60 and 50 mm and compared the wildlife occupancy of nest boxes with these three entrance diameters. We found that Common brushtail possums, a predator of cavity‐nesting birds and eggs, were significantly less likely to occupy nest boxes with reduced entrance diameters and were excluded from nest boxes with a 50‐mm entrance diameter. Squirrel gliders occupied nest boxes with all three entrance diameters. Introduced species, namely the Common myna and the European honeybee, also occupied nest boxes with restrictor plates. Installation of nest boxes with reduced entrance diameters is a simple and effective strategy to exclude brushtail possums from nest boxes. However, a reduced entrance diameter cannot exclude other non‐target species, and we suggest that other exclusion strategies should be used in conjunction with reduced entrance diameters to increase the occupation of nest boxes by native birds.

Are Urban Populations of a Gliding Mammal Vulnerable to Decline?

Small populations are at high risk of extinction, and they are likely to need management intervention. Successful management, however, relies on sufficient long-term demographic data in order to determine whether apparent declines are natural fluctuations or the product of threatening processes. In this study, we monitored a small urban population of squirrel gliders (Petaurus norfolcensis) in Queensland, Australia, over a 16 year period. A reference population in a larger forest patch was also studied in order to investigate whether its demographic trends were similar. Using mark-recapture data to generate estimates of apparent survival and population size, we found evidence of a decline within the small population but not in the reference population over the monitoring period. We suggest that the influence of multiple factors may have led to the decline, but, ultimately, that the genetic condition of the small population may be responsible. Understanding demographic trends is an important context for management interventions of small populations, although causes of decline need to be identified for successful management. The squirrel glider provides a useful case study for small urban populations and particularly for arboreal mammals.

Flexible Employment of Torpor in Squirrel Gliders (Petaurus norfolcensis): An Adaptation to Unpredictable Climate?

AbstractTorpor is a highly effective response to counter various ecological and physiological bottlenecks in endotherms. In this study, we examined interrelations between thermoregulatory responses and key environmental variables in free-living squirrel gliders (Petaurus norfolcensis) in a habitat with drastic climatic and ecological changes across seasons. To this end, we measured body temperature (Tb) and heart rate (fH) simultaneously throughout the year using implanted data loggers. Squirrel gliders in our study experienced fluctuations in ambient temperature (Ta) between -4.0°C and 44.1°C and expressed torpor at different times during the year. In contrast to our expectations, torpor seemed to be employed flexibly, on demand, and most frequently in spring rather than during the coldest and/or hottest periods. Torpor bouts lasted, on average, about 5 h, and Tb during torpor dropped as low as 17.9°C. The fH during torpor decreased below 50 bpm, which is about one-third of the basal level. The ability to record fH alongside Tb enabled us to also report periods of low fH during thermoconforming hyperthermia at Ta's above 35°C that likely occurred to conserve energy and water. Our findings double the body size of Australian gliders for which data on torpor are available and advance our ecological understanding of the dynamics of torpor expression in wild mammals and of how animals cope with varying conditions. Moreover, they highlight that the flexibility of physiology and thermoregulatory responses are clearly more complex than previously thought.

Observations of interference competition between the introduced black rat and native marsupial gliders in Australia

AbstractIntroduced rodents, particularly the black rat (Rattus rattus), have caused serious ecological impacts due to their ability to interact with native species as both predators, and by eliciting competitive pressure. However, impacts of black rats upon many Australian mammals have yet to be determined, particularly when those mammals are arboreal. Here, we present novel observations in the form of camera trap footage and photographs of interspecific competition between the introduced black rat and two species of arboreal gliding marsupial (sugar gliders (Petaurus breviceps) and squirrel gliders (Petaurus norfolcensis)) in urban bushland reserves in New South Wales, Australia. Gliders were found to flee or were prevented from exploiting food resources due to antagonistic posturing and physical attacks by black rats. While interspecific aggression and interference competition between black rats and native mammal species has been demonstrated previously, this appears to be the first observation of such interactions for Australian gliders. Our findings may have implications for the future management of glider populations in urban bushland where they co‐occur with rats; however, further research needs to be undertaken to determine the extent of this potential threat.

Genome-wide SNPs detect fine-scale genetic structure in threatened populations of squirrel glider Petaurus norfolcensis

Australian arboreal mammals are experiencing significant population declines, particularly due to land clearing and resulting habitat fragmentation. The squirrel glider, Petaurus norfolcensis, is a threatened species in New South Wales, with a stronghold population in the Lake Macquarie Local Government Area (LGA) where fragmentation due to urbanization is an ongoing problem for the species conservation. Here we report on the use of squirrel glider mitochondrial (385 bp cytochrome b gene, 70 individuals) and nuclear DNA (6,834 SNPs, 87 individuals) markers to assess their population genetic structure and connectivity across 14 locations sampled in the Lake Macquarie LGA. The mitochondrial DNA sequences detected evidence of a historical genetic bottleneck, while the genome-wide SNPs detected significant population structure in the Lake Macquarie squirrel glider populations at scales as fine as one kilometer. There was no evidence of inbreeding within patches, however there were clear effects of habitat fragmentation and biogeographical barriers on gene flow. A least cost path analysis identified thin linear corridors that have high priority for conservation. These areas should be protected to avoid further isolation of squirrel glider populations and the loss of genetic diversity through genetic drift.

Population viability analysis using Bayesian networks

Traditional population viability analysis (PVA) does not address the degree of measurement error or spatial and temporal variability of vital rate parameters, potentially leading to inappropriate conservation decision-making. We provide a methodology of applying Bayesian network (BN) modeling to PVA addressing these considerations, particularly for species with complex stage-class structures. We provide examples of three species from eastern Australia - hip pocket frog (Assa darilingtoni), squirrel glider (Petaurus norfolcensis) and giant burrowing frog (Heleioporus australiacus), comparing traditional matrix-based PVA with BN model analyses of mean stage abundance, quasi-extinction probability, and interval threshold extinction risk. Both approaches project similar population sizes, but BN PVA gave more clearly identifiable thresholds of population changes and extinction levels. The PVA BN uniquely represents complex stage-class structures and in a single network, including variation and uncertainty propagation of vital rates, to better inform conservation management decisions.

Genome-Wide SNPs Detect Hybridisation of Marsupial Gliders (Petaurus breviceps breviceps × Petaurus norfolcensis) in the Wild.

Petaurus breviceps and Petaurus norfolcensis have produced hybrids in captivity, however there are no reported cases of Petaurus hybridisation in the wild. This study uses morphological data, mitochondrial DNA, and nuclear genome-wide SNP markers to confirm P. breviceps breviceps × P. norfolcensis hybridisation within their natural range on the central coast of New South Wales, Australia. Morphological data identified a potential hybrid that was confirmed with next-generation sequencing technology and 10,111 genome-wide SNPs. Both STRUCTURE and NewHybrid analyses identified the hybrid as a P. norfolcensis backcross, which suggests an initial F1 hybrid was fertile. The mitochondrial DNA matched that of a P. b. breviceps, indicating that a P. b. breviceps female initially mated with a P. norfolcensis male to produce a fertile female offspring. Our study is an important example of how genome-wide SNPs can be used to identify hybrids where the distribution of congeners overlaps. Hybridisation between congeners is likely to become more frequent as climate changes and habitats fragment, resulting in increased interactions and competition for resources and mates.

Large area used by squirrel gliders in an urban area, uncovered using GPS telemetry.

The squirrel glider (Petaurus norfolcensis) is a threatened, gliding marsupial that persists in fragmented landscapes despite its restricted capacity to cross large gaps. As measures to maintain and/or restore suitable habitat depend on knowledge about the species' ecological requirements, we investigated the area used by squirrel gliders in an urban area near Newcastle, Australia. Using GPS telemetry data and the autocorrelated kernel density estimator, we estimated area used to average 10.8 ha and varied from 4.6 to 15 ha, which is equal to or greater than found in previous studies that spanned longer time periods. This has implications when identifying the minimum patch size necessary for ensuring the long‐term conservation of a squirrel glider population.

Insulated nest boxes provide thermal refuges for wildlife in urban bushland during summer heatwaves

Abstract In urban bushland, the installation of nest boxes is widely used to compensate for the loss of natural tree hollows. However, current nest box designs may not provide thermal refuges for wildlife during summer heatwaves, particularly if internal temperatures exceed the upper critical temperatures of wildlife. We investigated whether the addition of roofing insulation to nest boxes deployed for sugar gliders (Petaurus breviceps) and squirrel gliders (Petaurus norfolcensis) in urban bushland would reduce internal nest box temperatures during summer heatwaves. We measured temperatures of 44 insulated and 47 uninsulated nest boxes during one of the hottest summers on record (2018–2019) in the Lake Macquarie region of NSW, Australia, a period during which several prolonged heatwaves occurred. Over the 90-day study, maximum temperatures were, on average, 3.1°C lower in insulated boxes than in uninsulated boxes. The addition of insulation significantly lowered nest box temperatures regardless of aspect (north or south facing) or day of measurement. Temperatures exceeded the upper critical temperature (35.1°C) of gliders more frequently in uninsulated nest boxes (28% of days) than in insulated nest boxes (8% days). Although the addition of insulation to nest boxes lowered their internal temperatures, during heatwaves spanning 23 days, nest box temperatures exceeded the upper critical temperatures of gliders on 58% and 23% of days in uninsulated and insulated nest boxes respectively. These findings underscore the importance of retaining natural hollows in urban bushland to provide thermally suitable refuges for wildlife during extreme heat events.

Choice of monitoring method can influence estimates of usage of artificial hollows by vertebrate fauna

The loss of hollow-bearing trees is a key threat for many hollow-dependent taxa. Nesting boxes have been widely used to offset tree hollow loss, but they have high rates of attrition, and, often, low rates of usage by target species. To counter these problems, chainsaw carved hollows (artificial cavities cut into trees) have become a popular alternative, yet little research has been published on their effectiveness. We examined the usage of 150 chainsaw carved hollows by cavity-dependent fauna in the central west of New South Wales using observations from traditional inspection methods and remote cameras. Between October 2017 and April 2019, we detected 21 species of vertebrates (two reptile, one amphibian, 10 bird, and eight mammal species) inside chainsaw carved hollows, but the number of species detected was dependent on the chosen monitoring method. We detected six species inside hollows during physical inspections, whereas remote cameras detected 21 species entering hollows. Cameras detected eight species using hollows as breeding sites, whereas physical inspections detected just four species. Cameras detected two threatened mammals (squirrel glider (Petaurus norfolcensis) and greater glider (Petauroides volans)) raising young inside hollows, yet we failed to detect these species during physical inspections. For birds, the two methods yielded equivalent results for detection of breeding events. Overall, our study showed that few cavity-dependent species used chainsaw carved hollows as breeding sites. This highlights how artificial hollows are not a substitute for retaining naturally occurring hollows in large trees and revegetation programs.

Comparison of spotlighting and trapping in population surveys of the squirrel glider

Population monitoring of arboreal mammals should be informed by estimates of detection probabilities from different methods. We employed trapping and spotlighting across 36 transects to detect the squirrel glider (Petaurus norfolcensis). Repeat surveys were conducted over five sessions. We used multi-method occupancy to compare these methods. The probability of detection did not differ between one night of spotlighting (0.23 ± 0.04, mean ± s.e.), or one night of trapping (0.22 ± 0.03). Trapping continued for three nights, which led to the probability of detection rising to 0.41 ± 0.04. Spotlighting was only conducted once per session. These methods would require equivalent effort when conducted over three nights. Further investigation is required to compare this and other methods such as camera trapping and spotlighting with thermal cameras.

The conservation of arboreal marsupials in the Albury‐Wodonga region of south‐eastern Australia

SummaryUrban expansion is a major cause of land use change and presents a significant threat to biodiversity worldwide. Agricultural land is often acquired by local councils and developers to expand urban growth boundaries and establish new housing estates. However, many agricultural landscapes support high biodiversity values, especially farmlands that feature mosaics of native vegetation and keystone habitat such as hollow‐bearing trees. In south‐eastern Australia, many arboreal marsupials including the threatened Squirrel Glider (Petaurus norfolcensis) have populations within peri‐urban zones of expanding rural cities. A key challenge to planners, developers and conservation organisations is the need to maintain habitat for locally rare and threatened species as land undergoes changes in management. Critical to the sustainable development of peri‐urban landscapes is a thorough understanding of the distribution, habitat requirements and resources available to maintain and improve habitat for species dependent on limited resources such as tree cavities. In this management report, we present background information on an integrated research programme designed to evaluate potential impacts of urban development on fauna in the Albury Local Government Area, NSW. We mapped hollow‐bearing trees, erected nest boxes and monitored arboreal marsupials. Information presented in this report provides a blueprint for monitoring arboreal marsupials, including threatened species in other developing regions, and will assist the Albury‐Wodonga local governments in future planning of sustainable living environments.

Geographic variation in body size of five Australian marsupials supports Bergmann’s thermoregulation hypothesis

Abstract Despite a large body of research, little agreement has been reached on the ultimate driver(s) of geographic variation in body size (mass and/or length). Here we use skull length measurements (as a surrogate for body mass) from five Australian marsupial species to test the primary hypotheses of geographic variation in body size (relating to ambient temperature, productivity, and seasonality). We used a revised articulation of Bergmann’s rule, wherein evidence for thermoregulation (heat dissipation or heat conservation) is considered supportive of Bergmann’s rule. We modeled the skull lengths of four Petaurid glider species and the common brushtail possum (Trichosurus vulpecula) as a function of indices of ambient temperature, productivity, and seasonality. The skull length of Petaurus ariel, P. notatus, and the squirrel glider (P. norfolcensis), increased with increasing winter minimum temperature, while that of T. vulpecula decreased with increasing summer maximum temperature. The skull length of P. ariel decreased with indices of productivity, falsifying the productivity hypothesis. Only P. ariel met the hypothesis of seasonality, as skull length increased with increasing seasonality. Thermoregulation was the most consistently supported driver of geographic variation in body size, as we found evidence of either heat conservation or heat dissipation in four of the five species examined. We found the geographic range of the individual species and the climate space in which the species occurred was integral to understanding the species’ responses to climate variables. Future studies should use specimens that are representative of a species’ entire geographic range, encompass a variety of climatic regions, and use consistent methodologies and terminology when testing drivers of geographic variation in body size.

Nest box contentions: Are nest boxes used by the species they target?

SummaryNest boxes have grown in popularity as a habitat management tool in Australia during the last decade. This management use remains contentious because some studies suggest nest boxes are ineffective. There are three recent contentions: (i) nest boxes mostly benefit common species, (ii) exotic species may be dominant users of nest boxes, and (iii) species of conservation concern use nest boxes infrequently. We address these contentions using data from 1865 nest boxes involving eight nest box designs. These nest boxes were installed predominantly <200 m from a road in association with highway duplication and re‐alignment across 16 projects in New South Wales. The Common Brushtail Possum (Trichosurus vulpecula) is the species of most relevance to contention 1. It used 9% of boxes overall including 26% of ‘possum’ designated boxes. The most frequent nest box users were small petaurid gliders (mostly Sugar Gliders, Petaurus breviceps) which used 63% of ‘small glider’ designated boxes. This nest box and another suited to the Sugar Glider comprised 40% of all boxes installed, so it is not surprising that this species might be a common user. Exotic species were uncommon users of the nest boxes enabling contention 2 to be rejected. Active hives of Feral Honeybees (Apis mellifera) occupied just 1% of boxes, and another 1% of boxes were used by introduced rodents and birds. The Squirrel Glider (Petaurus norfolcensis) is the species most relevant to contention 3. It was seen in 80 boxes across 11 projects, representing 7% of the three types most frequently used. These observations are not consistent with the third contention. Nest boxes can provide many important insights about the requirements and interactions of hollow‐dependent fauna. However, they are not intended as an alternative to retaining hollow‐bearing trees.

Phase variation in latB associated with a fatal Pasteurella multocida outbreak in captive squirrel gliders

A septicaemic disease outbreak caused by Pasteurella multocida at a zoo in Western Australia (Zoo A) occurred in a resident group of squirrel gliders (Petaurus norfolcensis) following the introduction of two squirrel gliders imported from another zoo (Zoo B). P. multocida isolates obtained from the affected animals and asymptomatic, cohabiting marsupials at both zoos were typed via lipopolysaccharide outer core biosynthesis locus (LPS) typing, repetitive extragenic palindromic PCR (Rep-PCR) typing, and multilocus sequence typing (ST). Investigation of isolate relatedness via whole genome sequencing (WGS) and phylogenomic analysis found that the outbreak isolates shared the same genetic profile as those obtained from the imported gliders and the positive marsupials at Zoo B. Phylogenomic analysis demonstrated that these isolates belonged to the same clone (named complex one), confirming that the outbreak strain originated at Zoo B. As well, the carriage of multiple different strains of this pathogen in a range of marsupials in a zoo setting has been demonstrated. Importantly, the genomic investigation identified a missense mutation in the latB, a structural LPS gene, resulting in introduction of an immediate stop codon in the isolates carried by asymptomatic squirrel gliders in Zoo B. The identified diversity in the latB gene of LPS outer core biosynthesis loci of these isolates is consistent with a novel phase variable mechanism for virulence in P. multocida.Our study demonstrates the benefit of WGS and bioinformatics analysis in epidemiological investigations of pasteurellosis and its potential to reveal unexpected insights into bacterial virulence.

Long-term monitoring of nest boxes and nest logs in a tree-hollow depleted box–ironbark forest in north-eastern Victoria

Forest and woodland areas that have suffered historic degradation of habitat are likely to have reduced populations of tree-hollow dependent wildlife. We investigated the frequency of use of small-entry nest boxes installed 3 m high and vertical nest logs installed 1–3 m high, over 10–30 years in box–ironbark forest in north-east Victoria. Mammals were the dominant users of the nest boxes. Squirrel gliders and sugar gliders collectively used >75% of boxes and brush-tailed phascogales used >30% of boxes. Birds used the nest boxes on just two occasions. Brown treecreepers were the dominant users of the nest logs, with 48 breeding events across 30% of 105 nest logs. Turquoise parrots bred in the logs on five occasions. Gliders used 31% and phascogales 16% of the nest logs. These mammals were directly observed more frequently in the nest boxes than in the nest logs. Our findings show that mammals and birds preferred morphologically different hollows. Further research into the influence of different artificial hollow design elements is required. Nest boxes and nest logs required infrequent maintenance that was easily sustained over time. Our results suggest that tree-hollow dependent wildlife can benefit from restoration of their breeding and shelter sites.

The gaits of marsupials and the evolution of diagonal-sequence walking in primates.

Documenting the variety of quadrupedal walking gaits in a variety of marsupials (arboreal vs. terrestrial, with and without grasping hind feet), to aid in developing and refining a general theory of gait evolution in primates. Video records of koalas, ringtail possums, tree kangaroos, sugar gliders, squirrel gliders, wombats, numbats, quolls, a thylacine, and an opossum walking on a variety of substrates were made and analyzed to derive duty factors and diagonalities for symmetrical walking gaits. The resulting distributions of data points were compared with published data and theories. Terrestrial marsupials' gaits overwhelmingly plot slightly below the theoretical "horse line" (Cartmill et al., Zoological Journal of the Linnean Society. 2002;136:401-420) typical of terrestrial mammals; arboreal marsupials' gaits overwhelmingly plot more decisively above it. Both distributions are roughly parallel to the horse line, but arboreal animals exhibit increased diagonality, so that their higher-speed walking gaits overlap with those of typical primates on the Hildebrand diagram of diagonality against duty factor. Quadrupeds avoid gaits lying exactly on the (theoretically optimum) horse line, to avoid fore/hind limb interference ("forging"). This can be accomplished by either a slight reduction in diagonality ("downshifting") or a more decisive increase ("upshifting"). Tree-dwellers adopt the second option to eliminate unilateral bipods of support from the gait cycle. The upshifted horse line represents an early phase in the evolution of primate-like diagonal-sequence gaits.

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.

Video monitoring reveals novel threat to Critically Endangered captive-bred and released Regent Honeyeaters

ABSTRACTNest predation is a primary cause of nest failure in open-cup nesting woodland birds and low reproductive success is a common reason why reintroduced species fail to establish in the wild. We used video monitoring to record the breeding outcomes and identify the causes of nest failure in a reintroduced population of the Critically Endangered Regent Honeyeater. We intensively monitored 28 nesting attempts of 13 pairs during the 2015 breeding season, and found that the probability of individual nest success was 0.21 (from egg laying to fledging). We report for the first time Sugar and Squirrel Gliders depredating Regent Honeyeater nests. In addition to losses attributed to predation, a high proportion of chicks died in the nest from unknown causes. Our results show that rates of nest initiation and success are low in reintroduced Regent Honeyeaters, and future reintroductions should attempt to mitigate the threat of nest predation. Other sources of nest failure and barriers to nest initiation and egg laying are priority areas for future research.

Time budget of the squirrel glider (Petaurus norfolcensis) in subtropical Australia

Exudivorous mammals exploit food items of high quality and high rates of renewal, offset by wide dispersion and variable availability. How this influences foraging effort and size-related foraging efficiency remains poorly described. We examined the time budget of 5–6 male and 5–6 female squirrel gliders (Petaurus norfolcensis) during 6–8 nights in each of three seasons that were stratified by moon phase. Radio-collared gliders were observed during a series of 1-h focal observations from dusk until dawn. Feeding dominated the time budget, accounting for 78% of observation time, or 85% of time when combined with behaviours associated with foraging. Females appear to maximise feeding rates before entering the energetically demanding phase of late lactation. Little time was spent resting while outside the den. Longer nights and the full moon were associated with later emergence and earlier retirement times. Animals re-entered their tree-hollow dens during the night, representing 2% of activity in late spring, 18% in winter and 9% in autumn (10% overall). This behaviour may relate to predation risk and lactation demands. We reviewed the percentage of the time budget that petaurid gliders devoted to feeding and found no clear relationship with body size.