Ross L. Goldingay

Roads and wildlife: impacts, mitigation and implications for wildlife management in Australia

Roads can disrupt the population processes of vertebrate wildlife species through habitat fragmentation and vehicle collision. The aims of this review were to synthesise the recent literature on road impacts on wildlife, to identify gaps in our understanding of this topic and to guide future research and management in Australia. We reviewed 244 published studies from the last decade on road and vehicle impacts on wildlife conducted worldwide. A geographic bias was evident among the studies, with 51% conducted in North America, 25% in Europe, 17% in Australia and 7% across several other countries. A taxonomic bias was evident towards mammals (53%), with far fewer studies on birds (10%), amphibians (9%) and reptiles (8%), and some (20%) included multiple taxonomic groups. Although this bias is partly explained by large insurance and medical costs associated with collisions involving large mammals, it is also evident in Australia and signals that large components of biodiversity are being neglected. Despite a prevalence of studies on wildlife road mortality (34%), population impacts are poorly described, although negative impacts are implicated for many species. Barrier effects of roads were examined in 44 studies, with behavioural aversion leading to adverse genetic consequences identified for some species. The installation of road-crossing structures for wildlife has become commonplace worldwide, but has largely outpaced an understanding of any population benefits. Road underpasses appear to be an important generic mitigation tool because a wide range of taxa use them. This knowledge can guide management until further information becomes available. Global concern about the decline of amphibians should lead to a greater focus on road impacts on this group. Priorities for research in Australia include (1) genetic studies on a range of taxa to provide an understanding of life-history traits that predispose species to barrier effects from roads, (2) studies that examine whether crossing structures alleviate population impacts from roads and (3) studies that describe the behavioural response of frogs to crossing structures and that identify factors that may promote the use of suitable structures. A national strategy to mitigate the impacts of roads on wildlife populations is long overdue and must ensure that research on this topic is adequately funded.

The value of nest boxes in the research and management of Australian hollow-using arboreal marsupials

Nest boxes have been recognised as research and management tools for arboreal marsupials in Australia for over 20 years. We review the published literature with the aim of describing the scope of studies conducted in Australia thus far and providing guidance to future research. We recognise three types of application in research: (1) detection of species, (2) study of a species’ ecology, and (3) investigation of box designs preferred by different species. Several species of arboreal marsupial may be detected more readily in nest boxes than by conventional survey techniques, allowing description of key aspects of their ecology; e.g. feathertail glider (Acrobates pygmaeus), eastern pygmy possum (Cercartetus nanus) and brush-tailed phascogale (Phascogale tapoatafa). Identifying the most favoured nest-box design for any species has implications for detection and management uses of nest boxes. More research is needed but preliminary findings suggest that species prefer narrow entrance holes, while height of the nest box above 3 m may be inconsequential. We recognise three types of management application: (1) species introduction, (2) support of populations of endangered species, and (3) strategic placement such as to enhance habitat connectivity. Currently there have been few attempts to use nest boxes to manage arboreal marsupials but further research is needed to realise their potential as a management tool.

Characteristics of tree hollows used by Australian birds and bats.

Many hundreds of species of wildlife worldwide are dependent on tree hollows (cavities) for their survival. I reviewed the published literature for hollow-using Australian birds and microbats to document their tree-hollow requirements and to guide future research and management. Such information is vital to the conservation of these species. The hollow requirements of only 35 of 114 hollow-using bird species and 15 of 42 hollow-using microbat species were documented in some detail. This overall paucity of information limits the ability to manage for the future requirements of species. However, some generalisations can guide management until further studies are conducted. Most species used a variety of available tree species, and the extensive use of dead trees probably reflects the high likelihood of these trees containing hollows. Birds (other than large parrots) and bats chose hollow entrances of a size close to body width. Large parrots require large hollows, with a preference for large vertical spouts and trunk hollows. Few birds or bats demonstrated an absolute requirement for high (>10 m) tree hollows, with most (70%) using some hollows with entrances ≤5 m above ground. Temperature has been postulated to influence roost selection among microbats because it enables passive rewarming from torpor and there is some evidence from Australian bats to support this. Many studies suggest a future shortage of hollow-bearing trees. Currently, artificial hollows appear to be the most likely interim solution to address this. Knowledge of the natural hollow requirements of species can be used to refine artificial-hollow designs. An increase in research effort is needed to address the many gaps in knowledge that currently exist. Priorities for research include (1) many additional studies to document the characteristics of the hollow-bearing trees used by species of microbat, (2) the need to conduct long-term bioregional studies of hollow-bearing tree attrition to help identify where management responses are most needed and (3) investigating whether fire plays a significant role in the creation of tree hollows of a range of size classes and therefore may have a management use. Such information has broad relevance because it will provide ecological insight that can be applied to the management of hollow-using birds and bats elsewhere in the world.

Cutting the carnage: wildlife usage of road culverts in north-eastern New South Wales

Culverts have been used for a number of decades in Europe and the USA to reduce wildlife road-kills. In Australia, culverts have been employed by road authorities only relatively recently. This study used sand-strip surveys to investigate wildlife usage of nine purpose-built culverts along a 1.4-km section of the Pacific Highway at Brunswick Heads, north-east New South Wales. Surveys during two eight-day periods in spring and summer 2000 found 1202 traverses by wildlife through the culverts. Frequent culvert users were bandicoots (25% of traverses), rats (25%), wallabies (13%) and cane toads (14%). All culverts were used by these species, suggesting that at least several individuals of each species were involved. Infrequent users (each <2% of crossings) were possums, echidnas, lizards, birds and introduced carnivores. A koala was recorded crossing on two occasions. The long-nosed potoroo was observed in the surrounding habitat but was not confirmed traversing the culverts. Surveys for road-kills on this road section suggest that the exclusion fence bordering the highway prevented mammal road-kills and channeled mammals to the culverts. A single survey on a wet night found many frogs crossing the road surface and many were killed. This study confirms that culverts and exclusion fencing facilitate safe passage across a road for a range of wildlife species. This suggests that this form of management response to extensive road mortality of wildlife is appropriate and should be adopted more widely. However, this form of mitigation is not effective for frogs.

Can Road-Crossing Structures Improve Population Viability of an Urban Gliding Mammal?

Tree-dwelling mammals are potentially highly vulnerable to discontinuities in habitat created by roads. We used population modeling to assess the viability of a metapopulation of Australias largest gliding marsupial, the greater glider (Petauroides volans), occurring in forest remnants in the fastest- urbanizing region of Australia, where habitat is dissected by major roads. Crossing structures for arboreal mammals (consisting of a land bridge with wooden poles for gliding and adjacent rope canopy bridges) have been installed over an arterial road that separates two of these remnants (one large, one small). It is currently unknown whether this species will use the crossing structures, but available tree height and spacing do not allow a glide crossing, and fences with metal flashing prevent access to the road by terrestrial and arboreal mammals. Our modeling reveals that even a relatively low rate of dispersal facilitated by these structures would substantially reduce the probability of extinction of the smaller subpopulation. This rate of dispersal is plausible given the small distance involved (about 55 m). The inclusion of wildfire as a catastrophe in our model suggests that these two remnants may encounter an undesirable level of extinction risk. This can be reduced to an acceptable level by including inter-patch movement via dispersal among other forest remnants. However, this requires connection to a very large remnant 8 km away, through a set of remnants that straddle two motorways. These motorways create discontinuities in forest cover that are beyond the gliding ability of this species. Crossing structures will be required to enable inter-patch movement. A priority for future research should be whether the greater glider will use road-crossing structures. Loss of habitat and habitat connections is continuing in this landscape and is likely to have dire consequences for wildlife if land managers are unable to retain appropriate habitat cover with corridors and install effective wildlife road-crossing structures where large roads intersect wildlife habitat.

Gliding performance and its relevance to gap crossing by the squirrel glider (Petaurus norfolcensis)

Gliding mammals occur worldwide and many are subject to increasing levels of habitat fragmentation. Knowledge of their ability to cross tree-gaps by gliding is quite poor. We describe aspects of the gliding performance of the squirrel glider (Petaurus norfolcensis) based on recorded parameters of 85 glides of 73 individuals. Animals launched from a horizontal position ~1.7 m below the top of a tree and 2.3 m out from the main trunk. All but one glide was to the trunk of a tree, landing 5.7 m above the ground. Animals glided a mean of 21.5 ± 0.9 m (range 9–47 m) in a horizontal plane, with no significant difference between the sexes. Horizontal glide distance appears to reflect tree spacing where individuals were released. The mean glide angle was 28.5 ± 0.8°, with no significant difference between the sexes. We predict that trees beside roads that create a tree-gap of 20 m (two-lane road) or 43 m (four-lane road) will need to be a least 13 m and 25 m tall, respectively, to enable animals to safely glide across a road. Where trees are absent, 12-m-high wooden poles could be installed, requiring some in the median strip of four-lane roads.

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.

Population Recovery following Decline in an Endangered Stream-Breeding Frog (Mixophyes fleayi) from Subtropical Australia

Amphibians have undergone dramatic declines and extinctions worldwide. Prominent among these have been the stream-breeding frogs in the rainforests of eastern Australia. The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has been postulated as the primary cause of these declines. We conducted a capture-mark-recapture study over a 7-year period on the endangered Fleay’s barred frog (Mixophyes fleayi) at two independent streams (30 km apart) in order to assess the stability of these populations. This species had undergone a severe decline across its narrow geographic range. Mark-recapture modelling showed that the number of individuals increased 3–10 fold along stream transects over this period. Frog detection probabilities were frequently above 50% but declined as the populations increased. Adult survival was important to overall population persistence in light of low recruitment events, suggesting that longevity may be a key factor in this recovery. One male and female were present in the capture record for >6 years. This study provides an unambiguous example of population recovery in the presence of Bd.

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.