David J. Sharpe

The characteristics of squirrel glider (Petaurus norfolcensis) den trees in subtropical Australia

Effective management of tree-hollow-dependent wildlife requires a sound knowledge of the characteristics of the trees used for shelter or breeding. We used radio-tracking to identify the den trees of squirrel gliders (Petaurus norfolcensis) in south-east Queensland (Qld) and north-east New South Wales (NSW). Squirrel gliders used dead trees as well as 13 species of living tree for dens across the two locations. Dead trees accounted for a large percentage of dens (54% of 48 dens in Qld, and 50% of 18 dens in NSW) despite comprising only 3–10% of the forest (trees >20 cm diameter at breast height (dbh)) at each location. This preference is largely due to dead trees being more likely to contain hollows, accounting for 26–44% of available hollow-bearing trees. Mean den tree size (dbh) was 48.9 ± 2.4 cm in Qld and 62.8 ± 5.6 cm in NSW. Den entrance height averaged 6.8 ± 1.2 m in Qld and 11.9 ± 1.3 m in NSW. Fissures in the trunk and holes in branches were the most common of six hollow types used. At one location branch end hollows were ignored relative to their availability. Den entrances varied in size (2.5–12 cm wide) but most were ≤5 cm in diameter. Entrance size of hollows appears to be the hollow attribute of most importance to squirrel gliders. Monitoring of these den trees over several years revealed the collapse of three dead den trees at each location, which is equivalent to an annual loss of 3% of den trees. Further research is needed to determine whether this will lead to a future shortage of den trees.

Home Range of the Australian Squirrel Glider, Petaurus norfolcensis (Diprotodontia)

Abstract Knowledge of the home range of threatened species is basic to their management and conservation. We describe the home range of the squirrel glider (Petaurus norfolcensis), a threatened marsupial, in the central part of its geographic range in eastern Australia. Thirteen individuals belonging to 6 monogamous social groups were radiotracked for 2–9 months. The adaptive kernel (AK95%) estimate reached an asymptote at approximately 30 locations, giving a mean area of 6.2 ha ± 0.6 SE for the 9 gliders with >30 locations. The AK50% averaged 0.9 ± 0.2 ha, indicating that small core parts of the home range were used intensively. Home ranges of group members (AK95%) showed a high degree of overlap (77%) and when combined averaged 6.7 ± 1.0 ha. They overlapped substantially (50%) with adjacent glider groups but core areas (AK50%) within them overlapped by only 12%. Two of 5 available habitats were well represented in all group home ranges. Habitat dominated by coast banksia (Banksia integrifolia), a key winter nectar food resource, was overrepresented compared to its availability. Conservation measures for this species involving habitat retention or restoration must be informed by recognition of what comprises a preferred local habitat and its distribution.

Feeding behaviour of the squirrel glider in remnant habitat in Brisbane

The diet of the squirrel glider (Petaurus norfolcensis) was studied in a 45 ha forest remnant within an urban area close to Brisbane in south-east Queensland. Qualitative observations of feeding behaviour were conducted during each of 10 months between May 2002 and April 2003, on over 27 P. norfolcensis from at least 10 social groups. Four different feeding behaviours were recorded from 750 observations. Feeding from flowers accounted for 48% of the diet. Nectar and pollen were derived from 10 overstorey tree species, though forest red gum (Eucalyptus tereticornis) dominated because of its high abundance and protracted flowering period. Honeydew and lerp feeding accounted for 15% and 2% of all observations, respectively. Searching for arthropods accounted for 35% overall and occurred in 20 different tree species, where a range of substrates was used. Brushbox (Lophostemon confertus) was the most important; it was used in all seasons and accounted for 49% of these observations. These results contrast with assessment of the diet of P. norfolcensis at other sites where a greater range of broad food types was used. This may reflect the disturbed quality of the habitat at our site. However, these observations confirm the importance of eucalypt nectar in the diet of this species.

Population ecology of the nectar-feeding squirrel glider ( Petaurus norfolcensis ) in remnant forest in subtropical Australia

Context. Nectar is a temporally variable food resource. However, because few studies describe the population dynamics of nectar-feeding non-flying mammals, it is unclear how such populations are influenced by resource availability. Aims. We investigated the population ecology of the squirrel glider (Petaurus norfolcensis) in remnant forest in Brisbane, Australia, where nectar was a dominant food item. Methods. We used 36 tree-mounted traps to census a squirrel glider population inhabiting a 47-ha urban remnant over a 4-year period. Key results. A total of 201 gliders was captured 705 times in 3729 trap-nights (19% trap success). Population density peaked in the first year at ~1.6 individuals ha–1, and declined down to ~0.5 individuals ha–1 by the final year. This change in population density appeared to be mediated by annual variation in flowering intensity. Births occurred from March to November, peaking between April and July. All females >1 year old bred in each year of the study, with a mean litter size of 1.7 (n = 122). The overall natality rate was 1.9, indicating that females occasionally bred twice per year. The sex ratio was at parity in the pouch and in the trappable population. Gliders first entered the trappable population at 4 months of age, and persisted for a mean of 32 months. The maximum longevity was at least 6 years. Conclusions. The demographic characteristics of this squirrel glider population within remnant forest surrounded by urban development were similar to those reported elsewhere. Variation in nectar availability appears to have a substantial influence on the dynamics of squirrel glider populations. Implications. The substantial variation in population size driven by food availability raises concerns regarding the viability of small populations of nectarivorous non-flying mammals inhabiting remnant habitat.

Fine-Scale Genetic Response to Landscape Change in a Gliding Mammal

Understanding how populations respond to habitat loss is central to conserving biodiversity. Population genetic approaches enable the identification of the symptoms of population disruption in advance of population collapse. However, the spatio-temporal scales at which population disruption occurs are still too poorly known to effectively conserve biodiversity in the face of human-induced landscape change. We employed microsatellite analysis to examine genetic structure and diversity over small spatial (mostly 1-50 km) and temporal scales (20-50 years) in the squirrel glider (Petaurus norfolcensis), a gliding mammal that is commonly subjected to a loss of habitat connectivity. We identified genetically differentiated local populations over distances as little as 3 km and within 30 years of landscape change. Genetically isolated local populations experienced the loss of genetic diversity, and significantly increased mean relatedness, which suggests increased inbreeding. Where tree cover remained, genetic differentiation was less evident. This pattern was repeated in two landscapes located 750 km apart. These results lend support to other recent studies that suggest the loss of habitat connectivity can produce fine-scale population genetic change in a range of taxa. This gives rise to the prediction that many other vertebrates will experience similar genetic changes. Our results suggest the future collapse of local populations of this gliding mammal is likely unless habitat connectivity is maintained or restored. Landscape management must occur on a fine-scale to avert the erosion of biodiversity.

How effective is spotlighting for detecting the squirrel glider

Recent studies have questioned the reliability of spotlighting to detect certain species of arboreal marsupial or to provide an index of population size. This study assesses the reliability of transect spotlighting to detect the squirrel glider (Petaurus norfolcensis) by comparison with grid trapping. Trapping was conducted for 3–4 nights, approximately every second month during 2001. Spotlighting was conducted monthly along four transects through the grid. The two techniques combined showed that at least 7–11 gliders were present during most of 2001 in the spotlit area. Trapping detected 1–4 individuals per census within this area. Only one was detected during 4 of 6 census periods. Spotlighting detected 2–4 individuals during 9 of 12 census periods. We estimate that spotlighting surveys detected an average of 25% of the squirrel gliders present; trapping surveys detected an average of 21% of gliders. We conclude that spotlighting under suitable conditions by experienced personnel was equally effective as trapping in detecting and providing a population index of squirrel gliders at our site. The generality of this finding must be tested at other sites. A review of published studies involving transect spotlighting of arboreal marsupials found that most incorporated repeat traverses of transects to improve detection, and standardised abundance or density for comparing site categories. Thus, the conclusions of these studies should not be affected by recognition that spotlighting detects only a proportion of the actual population size of a given species. We recommend further studies to assess detection of arboreal marsupials by spotlighting surveys.

Variation in the home-range size of the squirrel glider ( Petaurus norfolcensis )

The home-range area of animals may vary geographically and in response to habitat quality. We investigated the size of squirrel glider (Petaurus norfolcensis) home ranges near Brisbane, Queensland, and at Tea Gardens on the central coast of New South Wales. Habitat at both sites had been partially cleared and had been subjected to grazing for several decades. Twelve gliders were tracked over an average of 3.5 months in Brisbane. The fixed kernel (FK95%) home-range estimate averaged 4.6 ± 0.7 (s.e.) ha while the minimum convex polygon (MCP100%) averaged 6.7 ± 1.5 ha. Six gliders were tracked over 1 month at Tea Gardens. The FK95% home-range estimate averaged 14.8 ± 2.4 ha while the MCP100% averaged 13.3 ± 3.1 ha. The Tea Gardens values are derived from relatively short periods and are likely to underestimate the areas used. This study demonstrates that home-range size can vary substantially in the squirrel glider. This has implications for understanding how this species responds to variation in habitat quality and highlights the need for site-specific studies to inform aspects of management.

Vocal behaviour of the squirrel glider (Petaurus norfolcensis)

We describe the vocal behaviour of the squirrel glider (Petaurus norfolcensis) from 465 h of observation across five sites in north-east New South Wales and south-east Queensland. A monosyllabic or polysyllabic nasal grunt was the most frequent call (56% of 208 calls); it ranged from single calls to sequences of up to 20-min duration (mean 2.1 min ± 0.6, s.e.) and was heard on 34% of nights (n = 83) at two sites. The rate of the nasal grunt showed a positive relationship with population density at one site. The nasal grunt was typically made when conspecifics were near the caller, but responses were infrequent (7% of observations). Call playback produced no discernable change in call response. The nasal grunt appears to regulate individual spacing by facilitating mutual avoidance, a function hypothesised to be an evolutionary precursor to the use of calls in territorial defence. Threatening calls were the next most common vocalisation (17% of calls) and were accompanied by scuffles and/or chases. They were also used when gliders were preyed upon and during animal handling. The calling behaviour of the squirrel glider confirms the importance of vocal communication among petaurid gliders.

Demographic parameters of the squirrel glider (Petaurus norfolcensis) in an urban forest remnant

Abstract. The effective management of species requires detailed knowledge of key population parameters. A capture–mark–recapture study of the squirrel glider (Petaurus norfolcensis) was conducted in an urban forest remnant in Brisbane, south-east Queensland. A total of 187 adult gliders (96 females, 91 males) was captured 620 times, in 19 sessions over a 4-year period. A Cormack–Jolly–Seber model was employed to estimate adult survival and abundance. Factors that may affect survival (e.g. sex, year, season) were included in population models. The overall probability of annual apparent survival was 0.49 ± 0.08. The capture probability over the duration of the study was 0.38 ± 0.03. The size of the local population was highest in the first year of the study (70–113 individuals) but then declined and generally remained low in the last two years. Apparent survival may include an unknown component of dispersal. However, our study area was mostly surrounded by a hostile urban matrix, so the effect of dispersal may have been minimal. Further studies that assess the survival of squirrel gliders are needed to assess the extent to which this parameter varies among localities.