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.

The influence of urban encroachment on squirrel gliders (Petaurus norfolcensis): effects of road density, light and noise pollution

Context Loss and degradation of habitat from urban development is a key threat to the squirrel glider (Petaurus norfolcensis), because its distribution coincides where most people live in Australia. Squirrel gliders are known to occur in or around urban fringes where native vegetation is retained; however, little is known about specific anthropogenic factors that may affect their persistence. Aims We investigated the relative influence of biophysical and urban factors on the use of large hollow-bearing Eucalyptus trees, which are a key resource for squirrel gliders. The study was located in a typical urban growth area located in southern New South Wales. Methods A stratified random sampling approach was used to survey squirrel gliders in urban and rural areas. Infrared, motion-sensor cameras were placed in 34 selected trees for 17 nights to record squirrel glider occupancy and activity. Data on urban (e.g. light and noise pollution levels, road and housing density) and biophysical (e.g. tree height, hollow-bearing tree density, vegetation cover) variables were recorded at each survey tree. Data were statistically analysed using general linear modelling approaches. Key results Squirrel gliders were detected more frequently in the rural matrix (23.4% of camera trap-nights) than in urban areas (9.5%). Model results showed that tree height, and the distance to neighbouring trees, had a significant influence on the occurrence and activity of squirrel gliders. Road density and light pollution were included in ‘best’ models to explain glider activity (a negative influence), and noise pollution negatively influenced glider occurrence. Although gliders used large trees in both urban and rural areas, activity generally decreased as levels of urbanisation increased. Conclusions and implications Access to and availability of key resources such as tall, hollow-bearing trees is critical for gliders to persist in urban environments. Squirrel gliders will tolerate human stressors such as roads, noise and light pollution to a certain extent, but impacts on population viability remain largely unknown. Novel solutions need to be developed to lessen the effects of anthropogenic factors (such as light and noise) on patches of native vegetation retained in urban areas for conservation purposes.

The value of countryside elements in the conservation of a threatened arboreal marsupial Petaurus norfolcensis in agricultural landscapes of south-eastern Australia--the disproportional value of scattered trees

Human activities, particularly agriculture, have transformed much of the world's terrestrial environment. Within these anthropogenic landscapes, a variety of relictual and semi-natural habitats exist, which we term countryside elements. The habitat value of countryside elements (hereafter termed ‘elements’) is increasingly recognised. We quantify the relative value of four kinds of such ‘elements’ (linear roadside remnants, native vegetation patches, scattered trees and tree plantings) used by a threatened Australian arboreal marsupial, the squirrel glider (Petaurus norfolcensis). We examined relationships between home range size and the availability of each ‘element’ and whether the usage was relative to predicted levels of use. The use of ‘elements’ by gliders was largely explained by their availability, but there was a preference for native vegetation patches and scattered trees. We found home range size was significantly smaller with increasing area of scattered trees and a contrasting effect with increasing area of linear roadside remnants or native vegetation patches. Our work showed that each ‘element’ was used and as such had a role in the conservation of the squirrel glider, but their relative value varied. We illustrate the need to assess the conservation value of countryside elements so they can be incorporated into the holistic management of agricultural landscapes. This work demonstrates the disproportional value of scattered trees, underscoring the need to specifically incorporate and/or enhance the protection and recruitment of scattered trees in biodiversity conservation policy and management.

Use and characteristics of nocturnal habitats of the squirrel glider (Petaurus norfocensis) in Australian temperate woodlands

In Australian temperate woodlands, most squirrel glider (Petaurus norfolcensis) habitats exist outside formal conservation reserves, often in highly fragmented agricultural landscapes. To conserve squirrel glider populations in such woodlands it is essential to define important habitats and understand how they are used. This study examines the nocturnal habitat use of squirrel gliders across five sites within an agricultural landscape in south-eastern Australia. Over a five-month period we radio-tracked 32 gliders to 372 nocturnal locations. We quantify characteristics of key nocturnal habitats and describe their use. Gliders were more likely to use large eucalypt trees, particularly yellow box (Eucalyptus melliodora) and mugga ironbark (E. sideroxylon). Nocturnal activity mostly took place high in the canopy of eucalypts, accounting for 74% of fixes. Multiple regression models revealed that feeding was more likely to occur in large, healthy trees close to drainage lines, with a preference for E. melliodora, when eucalypts were not flowering. Flowering trees were preferentially sought and were strongly associated with being large healthy trees that occur on ridges and upper slopes. Showing that the squirrel glider utilises key feeding structures (large healthy Eucalyptus trees) in different parts of the landscape at different times has direct management implications in the conservation and restoration of squirrel glider habitat, particularly in fragmented temperate woodland.

Characteristics of tree hollows used by Australian arboreal and scansorial mammals

Many species of non-flying mammal depend on tree hollows (cavities or holes) for shelter and survival. I reviewed the published literature on tree hollow use by Australian non-flying arboreal and scansorial mammals to provide a synthesis of tree hollow requirements, to identify gaps in knowledge and to stimulate future research that may improve the management of these species. The use of hollows was described in some detail for 18 of 42 hollow-using species. Most information was for possums and gliding possums, whereas dasyurid marsupials and rodents were largely neglected. The paucity of data for many species must be addressed because it represents an impediment to their conservation. Hollow abundance appears to be the primary determinant of tree preferences. This accounts for the frequent use of standing dead trees by most species. Most hollow-bearing trees used as dens were at least 100 years of age. Further studies that describe the dynamic processes that govern the availability of tree hollows are needed. The few studies that document attrition of hollow-bearing trees suggest that land managers need to improve strategies for the effective retention and long-term replacement of these trees.

Den trees, hollow-bearing trees and nest boxes: management of squirrel glider (Petaurus norfolcensis) nest sites in tropical Australian woodland

The squirrel glider (Petaurus norfolcensis) is an arboreal marsupial potentially impacted throughout its geographic range by the loss of hollow-bearing trees. We investigated the use of den trees and the availability of hollow-bearing trees near Mackay in the tropical north of the squirrel glider range where information was deficient. Mean den tree size (41.1 ± 2.9 cm (s.e.), diameter at breast height (dbh)) was significantly larger than that of available trees (27.5 ± 0.9 cm). Dead trees (stags) comprised 52% of 27 dens but comprised only 12% of available trees. This likely reflects the greater frequency of hollows in dead trees compared with other trees. Surveys found that 59% of 720 available trees contained hollows. A much lower percentage of trees in the 10–30-cm dbh size class were hollow-bearing (22%) compared with trees >30 cm (77%), and we view these smaller trees as those providing future den trees. Their density varied from 17 to 95 ha–1 among sites, which suggests that most sites have an adequate supply of future hollows. We installed 56 nest boxes to determine use by squirrel gliders. Only 20% were used after 3 years, but use was not influenced by the availability of tree hollows. Tree hollow availability appears adequate for the squirrel glider in these tropical woodlands but further studies are needed to understand the dynamic processes that govern this resource.

The use of hollow-bearing trees retained in multi-aged regenerating production forest by the Tasmanian common brushtail possum (Trichosurus vulpecula fuliginosus)

Context Hollow-bearing trees are frequently retained in timber-production areas as part of measures to mitigate against the impacts of forest harvesting on fauna, yet few studies have investigated the effectiveness of such measures. Such studies are essential for adaptive forest management. Aims The main aim of the present study was to evaluate the use of hollow-bearing trees retained in harvested and unharvested forest as den sites by the Tasmanian common brushtail possum. In particular, we examined the distribution and types of hollow-bearing trees used as den sites and whether or not their use in harvested sites was influenced by time since harvest. Methods Thirty brushtail possums were radio-tracked to their day-time den sites between March 2007–July 2007 and July 2008–October 2008, at five dry Eucalyptus forest sites (three regenerating after partial harvest with hollow-bearing trees retained inside the coupe and two in relatively undisturbed forest) in south-eastern Tasmania, Australia. Key results The brushtail possums tracked in the study denned primarily in hollow-bearing trees at both the harvested and unharvested sites. At sites regenerating 8 and 10 years after harvest, most den site locations were in trees retained outside the harvest area, in large patches. In contrast, at the site regenerating 17 years after harvest, isolated trees and small patches within the harvested area were used. Conclusions Hollow-bearing trees retained within harvest areas do provide habitat for hollow-dependent fauna such as the common brushtail possum and enable recolonisation of harvested areas in the medium term. However, in the short term these trees may not be used and hollow-bearing trees retained in the surrounding landscape are important for providing refuge as the harvested area regenerates. Implications The retention of hollow-bearing trees in harvested areas may be an effective measure at enabling recolonisation of harvested areas once suitable habitat regenerates, but it is also important to ensure that large patches of mature forest (containing hollows) are retained in the surrounding landscape to ensure the persistence of hollow-using fauna.

Nest use by western pygmy-possums (Cercartetus concinnus) (Marsupialia:Burramyidae) at Innes National Park, South Australia

We examined the nest use of 15 radio-tracked western pygmy-possums (Cercartetus concinnus) throughout one year for up to nine nights each at Innes National Park, South Australia. At least one pygmy-possum was followed in each of 12 months. Nest type and nest fidelity varied greatly; shallow burrows under debris were the most frequently used. Nest preferences of females with young remain unknown. The ability of C. concinnus to use a diversity of nest types over relatively short periods is likely to be an important survival strategy.

The use of den trees by the squirrel glider (Petaurus norfolcensis) in temperate Australian woodlands

Effective conservation relies on understanding the biology of particular species and how they use key resources. For many arboreal mammals, tree hollows are a key den site. We examined the use of tree hollows by the squirrel glider (Petaurus norfolcensis) in south-eastern Australia. Over a five-month study, individual squirrel gliders used multiple hollow trees (average = 7) as den sites. Den sites were often adjacent to areas where nocturnal activities took place. The average distance between den sites used by individual gliders on successive days was 218 m. Dens were often shared by an adult pair and a juvenile. Den trees were disproportionably used, with gliders showing preference for 1–2 primary den trees often located on steep slopes. Our findings have implications for the number and spatial arrangement of den trees needed to promote the conservation of populations of the squirrel glider, particularly where land is used for agriculture and livestock grazing.