Artificial structures designed to promote road-crossing by arboreal mammals are increasingly being installed in Australia but there is a limited understanding of their usefulness. We studied five 50–70-m-long rope-bridges (encompassing three designs) erected across the Pacific Highway, a major freeway in eastern Australia. Native arboreal mammals showed a willingness to explore these structures, being detected by camera traps on four rope-bridges. The vulnerable squirrel glider (Petaurus norfolcensis) crossed on one rope-bridge at least once every 4.5 weeks over a 32-week period. The feathertail glider (Acrobates pygmaeus), common ringtail possum (Pseudocheirus peregrinus) and the common brushtail possum (Trichosurus vulpecula) were detected on one of two rope-bridges that extended under the freeway at creek crossings. The feathertail glider was detected on all three rope-bridge designs. Our results suggest that rope-bridges have the potential to restore habitat connectivity disrupted by roads for some arboreal mammals. Further research is needed to refine the design and placement of rope-bridges as well as to determine whether these structures promote gene flow.
This study is part of a broader investigation that uses nest boxes to understand the ecological requirements of hollow-dependent wildlife.Summary Nest 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.
The installation of glide poles to enable gliding mammals to cross wide road corridors has become a common feature of highway upgrades in eastern Australia. While frequent use by small species has been well documented, records of use by large glider species are scant. During 15 months of camera monitoring of two glide poles in the median of the Pacific Highway at Halfway Creek, north-east New South Wales, yellow-bellied gliders (Petaurus australis) were detected on nine occasions. On three of these occasions, video footage captured glide launches across the northbound carriageway. Our study provides the first definitive evidence of repeated use of wooden glide poles by the yellow-bellied glider to cross a highway corridor. Glide poles, therefore, have the potential to restore functional connectivity for yellow-bellied gliders at locations where major roads bisect forest habitat.
Summary Major roads and highways disrupt ecological flows and create barriers or filters to the movement of many species of wildlife, including gliding mammals. Mitigating these impacts presents major challenges for road authorities. One approach has been the retention of forest vegetation in median strips to serve as ‘stepping stones’ for gliding mammals to cross road gaps otherwise beyond their glide capacity. A recently upgraded section of the Pacific Highway through tall open forest near Bonville in north‐east New South Wales retained forest within two 10‐ to 45‐m‐wide median strips separating each carriageway and a service road. We investigated whether Sugar Gliders (Petaurus breviceps) used these median strips to cross an 85 to 135 m‐wide road corridor. Three radio‐collared Sugar Gliders (one male and two females) moved between both highway medians and forest on either side of the road corridor during 32 days of radio‐tracking. Although the sample size is small, these results suggest that highway median strips, featuring mature vegetation with a major den tree, can provide ‘stepping stones’ for gliding mammals to cross a highway that would otherwise function as a movement barrier or filter. Longer‐term research with greater numbers of animals at this and other sites is required to determine whether such strips would be commonly used when den trees are absent and whether gliding via median strips may also increase road mortality of the species.
Road networks continue to expand globally with predictable effects on ecological systems. Research into the effectiveness of road underpasses and overpasses for wildlife has been concentrated in North America and Europe. In Australia, most studies of underpasses have been of relatively short duration and without reference sites to give context to the measured rates of use. We studied 5-7 road underpasses at two locations in eastern Australia over 2-3 years, comparing camera trap detections of animals in underpasses with those at nearby forest sites. Three species of large macropod (wallabies and kangaroos) were frequently detected in the underpasses, with some underpasses traversed 1-4 times per week, and in many cases exceeded detections in the forest. The lace monitor (Varanus varius) was detected in all underpasses, often once per week during spring and summer, and infrequently in the forest. At each location, a different small macropod species, including one regionally threatened, showed a higher probability of detection in one underpass compared with several of the forest sites. The vulnerable koala (Phascolarctos cinereus) was detected infrequently in underpasses and in the adjoining forest. The short-beaked echidna (Tachyglossus aculeatus) had a high probability of detection in a single underpass. The "prey-trap hypothesis" postulates that predators will exhibit increased activity at underpasses as a consequence of prey being funneled. We found the red fox (Vulpes vulpes) had high activity in some underpasses. However, its activity coincided less than expected with the activity of the mammals most at risk to it. Our results provide no consistent support for the "prey-trap hypothesis." Instead, our study confirms the generic value of underpasses for a range of medium-large mammals as well as one large reptile. Habitat adjoining underpasses exert a strong influence on their use and require greater consideration to maximize underpass use.
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