Hollow Abundance Research Articles

The influence of fire and termites on tree hollow development in an Australian tropical savanna

Tree hollows are important habitat resources for wildlife globally. In the tropical savannas of northern Australia, the abundance of tree hollows is influenced by both fire and termites. With the regular application of prescribed fire in these ecosystems, it is important to understand the implications of fire management on important habitat resources – especially when applied over the long-term. This study uses a long-term fire experiment (18 years of applied fire treatments) with targeted termite and tree hollow surveys to investigate how the proportion of stem hollowing and abundance of hollow entrances are affected by termites and different long-term fire regimes. We used sonic tomography in a novel application to non-destructively estimate tree stem hollowing. Trunk diameter was identified as the strongest predictor of both stem hollowing and hollow entrance abundance, with larger trees having a greater proportion of the stem hollowing and greater number of hollow entrances. The proportion of stem hollowing tended to be greater closer to the base of the tree, and the number of hollow entrances was greater in Eucalyptus miniata than E. tetrodonta. While the proportion of stem that was hollowed did not influence the number of hollow entrances, the presence of any hollowing at 1.3 m was associated with more hollow entrances. We did not detect an effect of fire activity on stem hollowing or the abundance of hollow entrances at the individual tree level, and it may be that these effects are only detectable at the stand level due to changes in tree demographics with varying fire regimes. As large trees tend to have more hollow entrances, management to promote habitat for wildlife should focus on fire regimes that avoid the loss of large trees in the landscape.

How an unprecedented wildfire shaped tree hollow occurrence and abundance—implications for arboreal fauna

BackgroundTree hollows are an important habitat resource used by arboreal fauna for nesting and denning. Hollows form when trees mature and are exposed to decay and physical damage. In the absence of excavating fauna, hollow formation can take up to 200 years in Australian temperate Eucalyptus forests, making tree hollows a critical but slow forming habitat feature. The increasing frequency and severity of wildfires due to climate change has led to increased concern about the landscape-scale loss of nesting space for arboreal fauna, including endangered species such as the folivorous southern greater glider (Petauroides volans). To understand patterns of nesting resource availability, we assessed drivers of hollow occurrence in southeastern Australian mixed-species Eucalyptus forests and quantified the effects of an unprecedented large-scale wildfire, the 2019/2020 Black Summer bushfires, on hollow occurrence and abundance.ResultsTree size and shape, as well as site productivity and topography, were important predictors for hollow occurrence both before and after the fires. The occurrence of the southern greater glider was strongly dependent on high proportions of hollow-bearing trees. While high fire severities had a negative impact on southern greater glider occurrence, the number of hollow-dependent arboreal species was not affected. While the wildfires significantly reduced hollow abundance, we did not find significant effects on hollow occurrence. Fires altered the relationship between tree size and hollow occurrence expressed as a change in the probability of hollow occurrence, with a higher likelihood at smaller tree sizes after the fires.ConclusionsOur findings suggest that post-fire nesting space may be reduced at the tree-scale, while at the stand-scale, hollow-bearing trees persist as biological legacies. These persisting trees can support the recovery of hollow-dependent arboreal fauna, such as the endangered southern greater glider by providing denning and nesting space. Hollow-bearing trees that survived the fires have the potential to form new hollows faster compared to undisturbed mature trees.

Habitat use by the eastern pygmy-possum in a coastal woodland–heathland mosaic

Understanding patterns of habitat use is required to conserve species and to manage their habitats. I used detections of 156 individual eastern pygmy-possums (Cercartetus nanus) within artificial cavities to investigate habitat use across 18 ha of a woodland–heathland mosaic. Detection of breeding females was highest in autumn (March to May) and winter, during the flowering period of Banksia ericifolia. Detection was over two times higher in woodland compared with heathland. This pattern was not influenced by variation in flowering or hollow abundance, which were equivalent across the two habitats. Protection from the weather may drive this pattern. Adult males were detected most frequently in autumn, coinciding with the beginning of female reproduction. They were detected equally in woodland and heathland. Why detection was lower in winter and spring is unclear but may arise from female aggression, forcing males to use natural shelters away from lactating females. Subadults were detected most frequently in spring and summer, coinciding with independence and dispersal. Subadults preferred woodland, reflecting where they were reared. This study has provided new insights into the behavioural ecology of this species, but further studies are needed to better understand how foraging and breeding influence shelter site use.

Landscape‐scale distribution of nest predators and its relationship with regent honeyeater nest success

AbstractOvercoming low breeding success is a major challenge for reversing population decline in threatened species. High nest predation rates are a common cause of low productivity in birds, but implementing evidence‐based management actions to reduce nest predation is challenging. Targeted breeding management requires a good understanding of where threatened species breed, the identity and distribution of nest predator species and the impact of these nest predators on breeding success. For rare and nomadic species, this information is hard to come by. The breeding success of regent honeyeater Anthochaera phrygia has declined over recent decades, and nest predation is the primary cause of breeding failure. We conducted point‐count surveys of nine avian and three mammalian nest predator species across 80% of the regent honeyeater’s contemporary breeding area in south eastern Australia. We used occupancy models to determine the presence of predator species at survey sites and spatial models to predict predator abundance and species richness across the breeding area. We incorporated predator predictions for regent honeyeater nest locations into nest fate and daily nest survival models. Predator abundance was correlated positively with tree hollow abundance and proximity to water and negatively with shrub cover. Regent honeyeater nest success showed no significant relationship with predator abundance or predator species richness. Given how abundant and widespread avian and mammalian nest predators were throughout the breeding area, improving regent honeyeater nest success is likely to require implementation of simultaneous nest protection measures to avoid potential compensatory nest predation. Further research is required to better understand the relationship between nest predator abundance and regent honeyeater nest success.

Nest box revealed habitat preferences of arboreal mammals in box‐ironbark forest

SummaryHabitat preferences need to be understood if species are to be adequately managed or conserved. Habitat preferences are presumed to reflect requirements for food, shelter and breeding, as well as interactions with predators and competitors. However, one or more of these requirements may dominate. Tree‐cavity‐dependent wildlife species are one example where shelter or breeding site requirements may dominate. We installed 120 nest boxes across 40 sites to target the vulnerable Brush‐tailed Phascogale (Phascogale tapoatafa) and the non‐threatened Sugar Glider (Petaurus breviceps). The provision of shelter sites where few of quality are available may enable better resolution of habitat preferences. Over three years, we observed the Brush‐tailed Phascogale at 17 sites, whereas the Sugar Glider was observed at 39 sites. We tested four broad hypotheses (H1–H4) relating to habitat that may influence occupancy by these species. There was no influence of hollow (cavity) abundance (H1) on either species suggesting our nest boxes had satisfied their shelter requirements. There was no influence of habitat structure (canopy and tree proximity) (H2) immediately around the nest box trees. We found no influence of distance to the forest edge (H3). Variables at and away from the nest box site that appear to reflect foraging substrates (H4) were influential on the Brush‐tailed Phascogale. Sugar Glider occupancy was only influenced by a single variable at the nest box site. The lack of influence of any other variables is consistent with the very high occupancy observed, suggesting most of the forest habitat is suitable when shelter sites are available. We found no evidence that the Sugar Glider reduced site use by the Brush‐tailed Phascogale.

Habitat requirements of an arboreal Australian snake (Hoplocephalus bitorquatus) are influenced by hollow abundance in living trees

The value of tree hollows (cavities) to wildlife is well documented among birds and mammals, however few studies focus on their importance for snakes. Given increasing concern about the global net loss of hollow-bearing trees, it is imperative that studies extend to other vertebrate classes that may be dependent on this structural habitat component. We tested the hypothesis that habitat selection of an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus), is primarily influenced by shelter requirements at multiple spatial scales. Consistent with our hypothesis, snake detection was biased towards a riparian ecosystem where hollow-bearing tree density was on average nine times greater than adjoining vegetation communities. In contrast, we found that the relative abundance of potential prey was equivalent among vegetation communities (frogs: P = 0.882; geckos: P = 0.306). At the microhabitat scale, snakes selected live hollow-bearing trees that were significantly larger (mean diameter: 74.5 cm ± 3.4, s.e.) than those otherwise available (42.4 ± 1.2 cm, s.e.) and estimated to be on average 111 years old. We recorded temperatures inside tree cavities to investigate whether the preference for live trees might be influenced by temperature buffering. Temperatures inside live trees were up to 16.4 °C below ambient in summer and 13.0 °C above ambient in winter. Temperature buffering was more pronounced in living trees (regression of cavity temperature against ambient, winter: r = −0.621; summer: r = −0.630) compared to dead trees (winter: r = −0.219; summer: r = −0.328), suggesting microhabitat selection may be driven by thermal requirements. Our study demonstrates the important role that mature, live hollow-bearing trees play in habitat selection by the pale-headed snake. It also suggests that the conservation of this species will be difficult in environments where such trees have been depleted due to land management practices. Managing forests for the persistence and recruitment of live hollow-bearing trees must be the primary conservation objective for threatened hollow-dependent fauna globally.

Characteristics of hollows and hollow‐bearing trees in semi‐arid river red gum woodland and potential limitations for hollow‐dependent wildlife

AbstractUp to 37 species of the birds and microbats inhabiting inland Australia are dependent on tree cavities for breeding or roosting. The river red gum (Eucalyptus camaldulensis), a well‐known hollow‐bearing tree species, occurs in linear semi‐arid woodland along thousands of kilometres of ephemeral river channels and is the only tree species that provides widespread, aggregated hollow resources across a landscape otherwise dominated by shrublands. Here we assess the type and quantity of hollows available along ephemeral rivers of the MacDonnell Ranges bioregion in central Australia and determine which characteristics of river red gums best predict the abundance and characteristics of different tree hollows, as first steps towards assessing the current availability of hollows in the region. Approximately a third of all river red gums sampled were hollow‐bearing, but individual trees with abundant hollows were rare. Further, 36% of hollows had an entrance ≤ 5 cm, and 37% had entrances which were 6–10 cm in diameter, whereas only 13% of hollows had an entrance diameter > 20 cm suitable for larger hollow‐using species. Large and high hollows only occurred on trees that did not display post‐disturbance resprouting. Trees with multiple and diverse hollows were rare and tended to be in advanced stages of senescence and had larger stems (82.3 ± 3.33 cm) and were taller (14.4 ± 0.53 m) compared to non‐hollow‐bearing trees (23.44 ± 1.68 cm, 8.0 ± 0.34 m). Further research is required to establish whether the current abundance of hollows and diversity of hollow types are limiting to cavity‐dependent wildlife, and to identify any threats to availability of hollows.

The effects of fire history on hollow-bearing tree abundance in montane and subalpine eucalypt forests in southeastern Australia

Hollow-bearing trees provide critical habitat resources for forest fauna, yet there is evidence of a ubiquitous decline in the large, old trees most likely to provide this resource. Fire can influence the formation and persistence of tree hollows. In this study, we investigated the effects of stand-level fire history and individual tree attributes on tree hollow abundance in two forest types in Namadgi National Park in the Australian Capital Territory: subalpine woodlands dominated by Eucalyptus pauciflora Sieber ex Spreng (snow gum); and tall-open E. delegatensis R.T.Baker (alpine ash) montane forest. These forests can be differentiated by their distinct response to fire; E. pauciflora resprouts following fire and E. delegatensis reproduces exclusively via seed. We employed a ground-based approach to measure 1044 trees across 36 sites selected by forest type and fire history as recorded since 1920. For both species, hollow abundance decreased with total fire count at stand level and increased for E. delegatensis in response to an extensive wildfire that occurred in the study area in 2003. The probability of a tree containing a hollow increased with tree diameter and if the tree was dead. Our results show that fire frequency and severity have strong implications for tree hollow abundance in montane and subalpine eucalypt forests.

Cyclones, fire, and termites: The drivers of tree hollow abundance in northern Australia’s mesic tropical savanna

Tree hollows are a vital wildlife feature, whose abundance and availability has declined in many regions due to broad-scale vegetation clearance, timber-harvesting, and disturbance such as fire. In the temperate forests and woodlands of eastern and southern Australia, the loss of large, old trees and associated tree hollows has severely impacted populations of hollow-dependent fauna. In the tropical savannas of northern Australia, many hollow-dependent mammals are in decline, and habitat simplification and resultant hollow limitation have been suggested as potential contributors to these declines. Hence, we sought to quantify the abundance of hollows, and identify the key drivers of this abundance in northern Australian savannas. We modelled the environmental and ecological correlates of hollow abundance across an extensive area of eucalypt savanna in Australia’s Northern Territory. We found that hollow abundance was significantly related to tree characteristics (size, species) and broad environmental gradients (annual rainfall, soil depth). Key disturbances – cyclones, fire, and termites – substantially disrupted these relationships and led to high variation in hollow abundance, even at a local scale. Hollow abundance across the study area was high by both Australian and global standards (hollows >5 cm entrance diameter: 88 ha–1, hollows >10 cm: 23 ha–1) and greatest in high rainfall areas (associated with the abundance of large eucalypts). Many arboreal mammal species in northern Australia have now contracted to higher rainfall parts of their former range (where hollows are at highest density); however such higher rainfall areas are also more likely to be affected by stochastic cyclonic events that can severely reduce the abundance of hollows. Hollow abundance was also affected by recent fire history and, in many areas, the current regime of frequent, high intensity fires will lead to marked reduction in this resource.

Influence of tree hollow characteristics on saproxylic beetle diversity in a managed forest

Tree hollows are key structures in forest ecosystems constituting long-lasting habitats and nutritional resources for many saproxylic arthropod species. Due to diverse microhabitat structures and conditions in tree hollows, they can support a broad range of species. However, in the past intensive management practices in parts of Europe reduced the abundance of tree hollows, resulting in a decrease and endangerment of species specialised in this tree habitat. We investigated 40 beech trees with hollows in 2014 and a subset of 23 of these trees in 2015 in a managed forest landscape in Germany. Using emergence traps we collected 89 beetle species of which 33% were on the Bavarian Red List. We described the tree characteristics, physical hollow characteristics, and their surrounding environment investigating their influence on α-diversity of non-Red List and Red List species. Furthermore, we investigated spatial (between tree hollows) and temporal (same tree hollow but different years) β-diversity, considering the importance of turnover and nestedness components on β-diversity. α-Diversity decreased with increasing decomposition of wood mould and increased with increasing area of hollow entrance in both years. Additional characteristics differed between years and between non-Red List and Red List species. β-Diversity was related to diameter at breast height, number of surrounding tree hollows, area of hollow entrance and a temperature gradient. We found a higher species turnover than nestedness between tree hollows and between years, indicating highly dynamic beetle communities spatially as well as temporally. To support and maintain the diversity of saproxylic beetles inhabiting tree hollows, the heterogeneity of microhabitats is important and should be supported by maintaining the diversity of differently structured and sized tree hollows.

Remotely‐sensed foliage cover and ground‐measured stand attributes are complimentary when estimating tree hollow abundances across relictual woodlands in agricultural landscapes

SummaryHollows, also known as tree cavities, are critical to the survival of many animal species but are too poorly mapped across landscapes to allow for their adequate consideration in regional planning. Managing cost is important, so we tested whether freely available satellite‐derived foliage projective cover and field‐measured stand attributes could be used separately or combined to predict tree hollow abundance in relictual Australian temperate woodlands. Satellite‐derived foliage projective cover revealed variation in woody vegetation densities both within mapped woodland remnants and cleared areas of the agricultural matrix. Plot‐based field assessment of the actual number of hollows in each one‐hectare site (n = 110 sites) revealed a relationship with foliage cover. Improvement of the model was achieved if site‐based estimates of the proportion of the canopy due to Eucalyptus species and the number of mature trees per hectare were included. Remotely sensed foliage cover can improve on traditional vegetation mapping for predicting hollow‐bearing tree and hollow abundances at landscape scales when managing hollow‐dependent fauna habitat across relictual woodlands in temperate Australian agricultural landscapes. At finer scales, the addition of other predictors is necessary to raise the accuracy of the predicted hollow densities.

Tree hollows and forest stand structure in Australian warm temperate Eucalyptus forests are adversely affected by logging more than wildfire

Ecologically sustainable forest management aims to maintain biodiversity values within managed forest ecosystems. A key habitat component within Australian forest ecosystems are hollow-bearing trees which are crucially important for fauna species requiring tree hollows for diurnal shelter and nesting. The effect of disturbance regimes, in particular logging and fire, on hollow dynamics is poorly understood. The aim of this study was to determine the relationships between logging intensity and fire frequency on hollow abundance and forest stand structural attributes in two different eastern Australian Eucalyptus forest types.We found that average stand tree diameter at breast height was negatively correlated to logging intensity. Logging intensity was negatively correlated with tree diameter at breast height (DBH), and the density of both hollow-bearing trees and hollows. Losses of hollow-bearing trees and hollows occurred through an interaction between logging intensity and fire frequency, resulting in an absence of recruitment of hollow trees. However in unlogged forest, fire was positively correlated to the density of hollows. Under a regime of frequent fire, in areas that have had some degree of logging activity, a net loss of hollows may occur. We recommend additional hollow recruitment trees be retained on logged sites in the future if no net losses of hollows are to occur in the future, or for wider unlogged buffers to be established adjacent to the cutting area.

Hollow occurrence and abundance varies with tree characteristics and among species in temperate woodlandEucalyptus

Tree hollows are a critical but diminishing resource for a wide range of fauna around the world. Conservation of these fauna depends on sustainable management of tree species that produce the hollows on which they depend. This study addressed the need for empirical data about intraspecific and interspecific variation in hollow occurrence and abundance in woodland trees in Australia. We measured and performed hollow surveys on 1817 trees of seven species of woodland Eucalyptus in central-western New South Wales, Australia. Trees were surveyed at 51 one-hectare sites and about 30% of trees surveyed had multiple stems. Generalized linear mixed models that accounted for nestedness of stems within trees and trees within sites detected a significant amount of variation in hollow occurrence and abundance. Models for individual tree stems of live trees showed hollow probability and abundance increased with diameter at breast height (DBH) and with increasing senescence (form). Stems of Eucalyptus microcarpa Maiden had a higher probability of having hollows than similar DBH stems of Eucalyptus camaldulensis Dehnh., Eucalyptus melliodora A.Cunn. ex Schauer or Eucalyptus populnea ssp. bimbil L.A.S.Johnson & K.D.Hill. Dead stems in live trees were more likely to have hollows than live stems of similar DBH. Each stem in a multi-stemmed tree had a lower probability of hollow occurrence and lower abundance of hollows than single-stemmed trees of similar DBH. For stems of dead trees, hollow occurrence and abundance increased with DBH and differed depending on stage of senescence. A comparison of our data with other studies indicates regional variation of hollow abundances within tree species.

Does nest box design influence use by the eastern pygmy-possum?

Managing the availability of shelter sites is central to the conservation of vertebrate wildlife dependent on tree hollows (cavities) because hollow abundance has been reduced in many landscapes and trees do not typically acquire hollows until they are at least 100 years old. Artificial hollows (nest boxes) provide one option to offset local shortages in tree hollows. However, knowledge of preferred designs is required for this to be effective. We investigated nest box preference by the eastern pygmy-possum (Cercartetus nanus), a small marsupial recognised as threatened across part of its geographic range in eastern Australia. We installed nest boxes of four different designs in each of 30 plots where tree hollows were scarce. Designs showed no significant difference in thermal profile. We captured 223 adult and subadult pygmy-possums within 78% of the 120 boxes. Breeding females used boxes more frequently than adult males and showed a preference among the designs whereas males did not. Females favoured plywood nest boxes over a PVC design offering a horizontal cavity. Use of the PVC design increased when repositioned to present a vertical cavity. Thus, breeding females are selective of the cavities used to rear young, which may limit local population size.

Double sampling to assess the accuracy of ground‐based surveys of tree hollows in eucalypt woodlands

AbstractGround‐based surveys of tree hollows often give poor estimates of hollow abundance in forests. Woodlands have shorter trees and a more open structure than forests, which may make hollows easier to detect. Therefore, one would expect ground‐based surveys of tree hollows to be more accurate in woodlands than in forests. We compared hollow counts from ground‐based and climbing surveys (double sampling) for four species of Eucalyptus trees in woodlands of central‐western New South Wales, Australia: E. camaldulensis Dehnh, E. melliodora A. Cunn. ex Schauer, E. microcarpa Maiden and E. populnea F. Muell. ssp. bimbil L.A.S. Johnson & K.D. Hill and E. melliodora A. Cunn. ex Schauer. Overall, 83% of hollow‐bearing trees and 93% of trees without hollows were correctly classified by ground‐based surveys. Mean difference in hollow counts of ground‐based surveys to climbed surveys was 1.7 hollows ± 0.2 SE (all species combined) with 91% of ground‐based hollow counts being within five of the actual number of hollows. The error in ground‐based counts of hollows in E. microcarpa was larger than for the other three species. Errors in all species resulted from both overestimation and underestimation of hollow abundance by ground‐based surveys. A larger error was associated with the detection of hollows located in branches compared with hollows located in the main trunk(s). Total number of hollows in the tree (based on climbing surveys), crown area or maximum trunk diameter were significant predictors of ground‐based survey accuracy. Overall, the accuracy associated with ground surveys was relatively high and generally error rates were lower than those published for forests.

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.

Habitat requirements of the endangered red-tailed phascogale, Phascogale calura

Context The red-tailed phascogale once occurred widely across semiarid and arid Australia, but is now confined to the southern wheatbelt of Western Australia. Its apparently extensive former range suggests a broad habitat tolerance, yet it is now reported primarily from remnant vegetation within farmland containing wandoo Eucalyptus wandoo and rock sheoak Allocasuarina huegeliana associations. Aims To establish the habitat requirements of phascogales with a view to understanding their current and likely future distribution and status. Methods We established presence or absence of phascogales at a number of sites within their current range, primarily by trapping, and then compared habitat attributes between the two classes of sites to establish those of apparent significance to species persistence. Key results Phascogales are widespread in suitable upland (wandoo–rock sheoak) and lowland habitat (riverine fringing vegetation of swamp sheoak Casuarina obesa, York gum E. loxophleba and wandoo). They occupy areas of remnant vegetation of varying sizes from very small to very large, many on private agricultural land. Large connected areas, such as riverine corridors and clusters of upland remnants appear important to their long-term persistence. Sites isolated by increasing distance from another occupied site tended to be unoccupied. Habitats occupied by phascogales typically had a greater canopy density and greater abundance of hollows than unoccupied sites. The presence of plants of the genus Gastrolobium, often cited as a key factor in the persistence of phascogales, did not appear to influence the presence or absence of phascogales. Conclusions Red-tailed phascogales currently occupy a broader range of habitats than identified in the literature and the role of some key aspects of habitat in protecting them from further decline may have been overstated. The presence of suitable hollows for nesting and shelter and a dense mid-storey canopy, perhaps to protect from predation by owls, are key features of suitable phascogale habitat. Implications Suitable habitat for phascogales appears widespread in the surveyed portion of the remaining range of the species, but is under threat over the longer term. Increasing salinity in lowland areas (which transforms woodland to samphire with a consequent long-term loss of nesting hollows), lack of fire in upland areas to maintain dense stands of rock sheoak and the increasing loss of corridors of vegetation along roadsides due to the widening of roads by local councils are all contributing to loss of habitat and habitat connectivity.

Microbats in a ‘leafy’ urban landscape: are they persisting, and what factors influence their presence?

AbstractUrbanization is an extreme form of habitat modification, but retention of native vegetation in bushland reserves may improve the ecological sustainability of cities. We focused on bats (Microchiroptera) and investigated the use of the urban matrix and surrounding bushland in a region of Sydney, Australia, where remnant bushland persists and gardens often support large trees. Ultrasonic surveys were conducted at 40 sites over one summer season in the backyard matrix, bushland remnants and surrounding National Parks to determine which species were present, and the influence of landscape elements and habitat characteristics on activity, species richness and presence of individual species. In total, 15 of the 17 microbat species known from the Sydney region were recorded in the study area. Yet only three of these species, Chalinolobus gouldii, Mormopterus species 2 and Miniopterus schreibersii were present in more than 40% of sites. Bat activity was significantly higher in remnant bushland on shale soils and in backyards, compared with sandstone gully and ridge remnants, or reference sites in nearby National Parks. Furthermore, species assemblages in urban areas were different from assemblages in reference sites. Of all the habitat characteristics examined, the amount of bushland within 0.5–3 km surrounding a site and tree density were the most common predictors of individual species presence, particularly rare species. Area of bushland, hollow abundance and average tree diameter were positively correlated with species richness, while tree diameter was the strongest predictor of total microbat activity. The proximity of large areas of bushland and the many trees remaining in residential areas of the northern ‘leafy’ suburbs of Sydney allowed the persistence of a range of bat species. The higher bat activity on fertile shale soils indicated that bushland remnants embedded within cities can have high conservation value for bats. Surveys in more urbanized areas of Sydney are needed to test predictions of the models derived in this study.

Change in habitat resources and structure near urban edges and its influence on the squirrel glider (Petaurus norfolcensis) in southeast Queensland, Australia

AbstractUrban landscapes often expose wildlife populations to enhanced edge effects where the biotic and abiotic attributes of native ecosystems have been significantly altered. While some species may respond favourably to edges, there are likely to be varying negative consequences for many forest‐dependent species. In particular, marsupial gliders are influenced by changes in forest composition and structure near edges due to highly specific feeding and nesting requirements, and a high reliance on tree cover to traverse a landscape. We addressed this problem using the squirrel glider (Petaurus norfolcensis) in the fragmented urban landscape of southeast Queensland, Australia. Analysis of variance was applied to determine differences in habitat resources and structure in relation to glider presence and trap success rates in forest fragment interiors compared with road (minor & major) and residential edge habitats. We postulate that an increased presence of squirrel gliders in sites adjacent to minor road and residential edges may be due to the availability of additional resources and/or varying dispersal opportunities. Conversely, forest fragment interiors contain a higher abundance of nest hollows and large trees, together with a greater floristic species richness providing more reliable seasonal foraging sources, which may explain the greater trap success rates of squirrel gliders in these sites. We conclude that while forest fragment interiors provide habitat suitable for year‐round use by greater numbers of squirrel gliders, the conservation value of some edge habitats that provide additional resources and dispersal opportunities should not be underestimated for forest‐dependent mammals; however, each edge type must be assessed individually.

Tree hollow incidence in Victorian state forests

Summary The availability of tree hollows in timber production forests is a contentious issue facing forest and wildlife managers in Australia. To integrate conservation priorities for hollow-dependent fauna in forest stewardship, public land managers need information on the quantity and spatial distribution of hollow-bearing trees. This information has previously been lacking, but an extensive hollows database exists in the Victorian Statewide Forest Resource Inventory (SFRI). We use the SFRI to estimate simple stand-level models for the density of hollow-bearing trees, and the density of hollow size classes. Models were of borderline predictive ability but were statistically significant. This is consistent with previous models of hollow incidence that have found hollow formation to be intrinsically stochastic. We then applied these models in a geographic information system (GIS) to generate spatial predictions of hollow availability in Victorian state forests. The resulting GIS layers are available from the Department of Sustainability and Environment (DSE) and are a valuable resource for forest and wildlife managers, researchers and the interested public. We also created tables describing hollow abundance for different forest types, and important stand-level trends in hollow availability emerged. We found that hollow density in ash forests (Eucalyptus regnans, Eucalyptus delegatensis) was consistently low and strongly influenced by the presence of non-ash species that are more susceptible to hollow formation. Hollows occurred in E. regnans forest at particularly low density, with less than 37% of trees having hollows until diameter exceeded 125 cm. The density of hollows in non-ash forests was comparatively greater, with more than 49% of trees containing hollows when their diameter exceeded 75 cm.