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Quantifying predation attempts on arboreal marsupials using wildlife crossing structures above a major road

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Abstract

11 We review eight years of monitoring data to quantify the number of predation attempts on 12 arboreal marsupials using canopy bridges and glider poles across a major road in southeast 13 Australia. We recorded 13,488 detections of arboreal marsupials on the structures, yet only 14 a single (and unsuccessful) predation attempt was recorded. 15

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... We suggest the use of camera traps installed on each end of the bridge to record video, in addition to direct observations, to improve behavior measurements of fear or anxiety. Other studies have used camera traps set to record video to monitor canopy bridge use and have been able to determine more detailed demographic characteristics of study subjects , and even predation attempts during bridge use and the reactions of the individual to predation (Soanes et al., 2017). ...
Article
Although artificial crossing structures are increasingly implemented by conservationists and wildlife managers to connect fragmented wildlife habitat, the study of artificial crossing structure design, particularly of canopy bridges, is an emerging field of study in primatology. We address this issue by evaluating five competing bridge models with varying width, material stiffness, and substrate spacing. We assessed bridge preference and performance by sampling the behavior of three species of Costa Rican monkeys ( Alouatta palliata : n = 4, Ateles geoffroyi : n = 3, Cebus imitator : n = 3). In a semi-wild setting, we used focal individual sampling with instantaneous recording once every minute for ten-minute intervals and all occurrences sampling whenever study subjects used the bridge. We hypothesized that monkeys prefer bridges that are more stable, and that are made of materials that resemble tree branches. During nearly 37 sampling hours we observed 119 crossing events. We found that study subjects prefer bridge models that are built using more rigid materials, such as the bamboo pole bridge, or wider bridges that offer more stability than narrower bridges. The bridge type and the materials used to build the bridges are both significant predictors of bridge use. While preference for bridges and their performance varies by species, the bamboo pole bridge model and the horizontal mesh bridge were preferred and performed best in our study. The simple liana bridge model was the least preferred by all species and performed poorly in comparison to the other models. Our findings will help us better understand how design and materials impact the use of canopy bridges by monkeys, which can help improve biological corridors and offer new information for the management and conservation of primates living near infrastructure corridors and other kinds of dangerous matrix.
... We suggest the use of camera traps installed on each end of the bridge to record video, in addition to direct observations, to improve behavior measurements of fear or anxiety. Other studies have used camera traps set to record video to monitor canopy bridge use and have been able to determine more detailed demographic characteristics of study subjects , and even predation attempts during bridge use and the reactions of the individual to predation (Soanes et al., 2017). ...
Article
Although artificial crossing structures are increasingly implemented by conservationists and wildlife managers to connect fragmented wildlife habitat, the study of artificial crossing structure design, particularly of canopy bridges, is an emerging field of study in primatology.We address this issue by evaluating five competing bridge models with varying width, material stiffness, and substrate spacing. We assessed bridge preference and performance by sampling the behavior of three species of Costa Rican monkeys (Alouatta palliata: n = 4, Ateles geoffroyi: n = 3, Cebus imitator: n = 3). In a semi-wild setting, we used focal individual sampling with instantaneous recording once every minute for ten-minute intervals and all occurrences sampling whenever study subjects used the bridge. We hypothesized that monkeys prefer bridges that are more stable, and that are made of materials that resemble tree branches. During nearly 37 sampling hours we observed 119 crossing events. We found that study subjects prefer bridge models that are built using more rigid materials, such as the bamboo pole bridge, or wider bridges that offer more stability than narrower bridges. The bridge type and the materials used to build the bridges are both significant predictors of bridge use. While preference for bridges and their performance varies by species, the bamboo pole bridge model and the horizontal mesh bridge were preferred and performed best in our study. The simple liana bridge model was the least preferred by all species and performed poorly in comparison to the other models. Our findings will help us better understand how design and materials impact the use of canopy bridges by monkeys, which can help improve biological corridors and offer new information for the management and conservation of primates living near infrastructure corridors and other kinds of dangerous matrix.
... Some authors discuss increased predation while using crossing structures for primate (Cuarón, 1995;Birot et al., 2020) and nonprimate species (Little et al., 2002;Mata Estacio et al., 2015). There is little evidence that this is a substantial risk (Hernández-Pérez, 2015;Soanes et al., 2017;Birot et al., 2020), and a study that attempted to mitigate predation with a box-tunnel design (Australian possums, order: Didelphimorphia), the modification was rarely used (Weston et al., 2011). In contrast, ground movement is fraught with risks from dogs (Anderson, 1986;Riley et al., 2015;Waters et al., 2017), hunters (Linder and Oates, 2011), and vehicles (Hetman et al., 2019). ...
Article
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For primates, canopy bridges can reduce the road barrier effect. Yet little information exists to predict species bridge use. We examined bridge use across a 9 km suburban road in Diani, Kenya, in three survey years (N bridges : 21 = 2004, 27 = 2011, 29 = 2020) by four sympatric species of monkeys. The asphalt road is 6 m wide with a 50 km/h speed limit. Roadside observers recorded ground (N = 4931) and bridge (N = 3413) crossings, crossing direction, and traffic volume. Colobus (Colobus angolensis palliatus), Sykes' monkeys (Cercopithecus mitis albogularis), and vervets (Chlorocebus pygerythrus hilgerti) used the bridges while baboons (Papio cynocephalus cynocephalus) rarely did. Crossing rates (Sykes'>vervet>colobus>baboon) did not fit our predictions based on species' attributes of stratum preference (arboreal>terrestrial) or body mass (small>large), while the interaction between these attributes was more informative. Crossings were bidirectional. Colobus crossed bridges during higher traffic volumes than on the ground, whereas we found the opposite for vervets. Sykes' monkeys crossed at similar traffic volumes on the ground and bridges. The mean annual bridge cost was USD 157, deriving a cost per crossing as < USD 0.10, though it undervalues the savings in ecosystem services, tourism benefits, and contributions to protecting colobus, a vulnerable species. While we consider this highly economical, funders and road engineers will ultimately determine if it is so.
... The prey-trap hypothesis suggests that over time, predators learn to exploit wildlife crossing structures to increase foraging opportunities [17,18]. Few reports of predation by wild predators in crossing structures have been reported [19][20][21]. Patterns of temporal co-occurrence between predator and prey and prey avoidance of crossing structures have also been observed [22]. In addition to wild predators, feral animals such as dogs may exploit crossing structures for the predation of wild prey species [18]. ...
Article
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Crossing structures are widely accepted mitigation measures used to offset the impacts of roads in ecologically sensitive areas that serve as important animal corridors. However, altered interspecies interactions at crossing structures may reduce the potency of these structures for some species and groups. Anecdotes of predation events at crossing structures have necessitated the assessment of predator–prey interactions at crossing structures. We investigated the ‘prey-trap’ hypothesis at nine crossing structures on a highway in central India adjacent to a tiger reserve by comparing the geometric mean latencies between successive prey, predator and free-ranging dog camera trap capture events at the crossing structures. Among all interactions, prey–predator latencies were the shortest, and significantly lower than prey–dog and predator–prey latencies. Prey–predator sequences involving wild dogs had the shortest average latencies (65.6 ± 9.7 min). Prey–predator latencies decreased with increasing crossing structure width; however, these crossing structures are also the sites that are most frequently used by wildlife. Results indicate that the crossing structures presently do not act as ‘prey-traps’ from wild predators or free-ranging dogs. However, measures used to alleviate such prospects, such as heterogeneity in structure design and increase in vegetation cover near crossing structures, are recommended.
... Both in Australia and internationally, research into wildlife roadkill since the latter part of the 20th century has been perceptive and encouraging (Harris et al. 2008;Hobday and Minstrell 2008;Ramp and Roger 2008;Fahrig and Rytwinski 2009;Beckman et al. 2010;McCall et al. 2010;Taylor and Goldingay 2010;Jones et al. 2011Jones et al. , 2014Roger et al. 2011Roger et al. , 2012Jones 2012;Bond and Jones 2013;Lunney 2013;Soanes et al. 2017;Grueber et al. 2018;Santori et al. 2018;Ascensão et al. 2019;Fox et al. 2019), with Forman (2010) declaring that road ecology now reaches across much of the globe. ...
Article
A challenge to understanding the impacts of roads on koalas is that their effects operate across multiple scales. To determine what conditions underlie koala roadkill, we looked at koala roadkill at two spatial scales – the entire state of NSW, and a local government area (Coffs Harbour) – for three road types (primary, arterial and local). We also subdivided the state data into three regions – coast, tableland and inland – to look at regional differences. Our analyses show that koala roadkill is ubiquitous across the distribution of koalas. Similar numbers of roadkilled koalas were recorded on each road type, but because of the vastly different total length of roads in the three types (local roads 122 755 km; arterial 79 706 km; primary 12 972 km) it is clear that an individual koala is more likely to be killed on a primary road than the other two road types. The pattern shown at the LGA scale is similar to that seen across the state. Habitat type adjacent to a road appears to have little influence on the likelihood of a koala being killed on the road. Mitigation measures can reduce koala roadkill, but there is a need to correctly assess the relative importance of koala roadkill compared with other factors that impact on koala populations when allocating resources to koala conservation. We conclude that roadkill is an ever-present threat which will remove an ever-increasing proportion of decreasing koala populations in NSW.
... By including multiple parameters in the study, these may also help in constructing bridges for other tropical arboreal mammals (van der Grift and van der Ree 2015). In particular, factors such as providing habitat cover to provide safety from predators and the elements may ensure maximum use of the bridges (Soanes et al. 2017). Even without these factors, here we have further illustrated that simple to construct bridges were integrated into the niche of Javan palm civets and Javan slow lorises, with use of bridges similar to how they use other structures in their natural habitats. ...
Article
Full-text available
Natural and artificial canopy bridges can be used to mitigate the effects of habitat fragmentation. Understanding the ecological factors that influence bridge use is imperative to the effective design and placement of this potential conservation intervention. Moonlight, seasonality and weather may influence the cost and risk of using bridges, potentially reducing their effectiveness. We installed five artificial waterline bridges and, between 2017 and 2019, monitored via camera trapping their use by Javan palm civets Paradoxurus musanga javanicus and Javan slow lorises Nycticebus javanicus. We used a weather station to record microclimate data (temperature and relative humidity) and calculated the illumination percentage of the moon. We tested the influence of moon luminosity, relative humidity, seasonality (Julian day) and temperature on the frequency of bridge use via Generalised Additive Models. Camera traps captured 938 instances of bridge use by civets, which was significantly lower than the reference value at moon luminosity > 90%, temperatures > 20 °C, humidity > 90%, and during the drier period (May–July). Camera traps captured 1036 instances of bridge use by lorises, which was significantly lower than the reference value during the drier period and higher than the reference value at temperatures > 20 °C. Lorises showed peaks in bridge use close to sunset and sunrise whereas civets showed peaks around 2 h after sunset and 2 h before sunrise. Our study illustrates the utility of simple-to-construct bridges by two sympatric nocturnal mammals facing severe habitat loss, with bridge use differing between those species according to abiotic factors. In particular, less use by both taxa during the drier season could suggest modifying placement of bridges or providing another intervention during that time. Camera traps were an excellent mechanism to record these differences and to validate the importance of the bridges, including during inclement weather and dark nights, when observations would be more difficult for human observers. By understanding the influence that abiotic factors have on the use of artificial bridges, we can improve bridge placement and construction to encourage use by a variety of species, particularly those threatened by habitat fragmentation.
... For a prey-trap to occur, predators would have to detect (i.e., visually or olfactorily) and encounter prey inside wildlife passages with sufficient frequency to develop search images (sensu [57][58][59]. Surprisingly, there have been no documented cases of predators killing prey in wildlife passages; there has only been one documented case of an (unsuccessful) predation attempt on an arboreal marsupial 25 and the presence of a carcass near a wildlife passage 19 . Both encounter rates and capture success by predators may be too infrequent in wildlife passages for predators to learn to associate them with hunting opportunities (sensu 60,61 ), or otherwise influence their foraging behaviour 62 , particularly if small and medium-sized predators hunt differently from larger predators. ...
Article
Full-text available
Wildlife passages are structures built across roads to facilitate wildlife movement and prevent wildlife collisions with vehicles. The efficacy of these structures could be reduced if they funnel prey into confined spaces at predictable locations that are exploited by predators. We tested the so-called prey-trap hypothesis using remote cameras in 17 wildlife passages in Quebec, Canada from 2012 to 2015 by measuring the temporal occurrence of nine small and medium-sized mammal taxa (< 30 kg) that we classified as predators and prey. We predicted that the occurrence of a prey-trap would be evidenced by greater frequencies and shorter latencies of sequences in which predators followed prey, relative to prey–prey sequences. Our results did not support the prey-trap hypothesis; observed prey–predator sequences showed no difference or were less frequent than expected, even when prey were unusually abundant or rare or at sites with higher proportions of predators. Prey–predator latencies were also 1.7 times longer than prey–prey sequences. These results reveal temporal clustering of prey that may dilute predation risk inside wildlife passages. We encourage continued use of wildlife passages as mitigation tools.
... We suggest the use of camera traps installed on each end of the bridge to record video, in addition to direct observations, to improve behavior measurements of fear or anxiety. Other studies have used camera traps set to record video to monitor canopy bridge use and have been able to determine more detailed demographic characteristics of study subjects , and even predation attempts during bridge use and the reactions of the individual to predation (Soanes et al., 2017). ...
Presentation
Although wildlife bridges have been shown to aid nonhuman primates by connecting fragmented habitats, the evaluation of crossing structure (CS) design is a fledgling field of study in primatology. To address this problem, we evaluated CS preference and performance among three Neotropical primate species (Alouatta palliatta, n=4 individuals; Cebus capucinus, n=3; and Ateles geofroyii, n=3) at a rescue center in Puerto Viejo de Talamanca, Costa Rica. We tested the hypothesis that the monkeys prefer bridges that are relatively stiff. Study subjects were given uniform access to five models varying in stiffness and width during 27 sampling hours in July 2015. Model preference and performance was assessed by sampling focal individuals’ behavior and estimating bridge crossing rates. Our results show that there was a clear difference between bridge models in crossing events (N=122, x2= 10.4335, df= 4, p=0.0337). The least popular model was used in 6.7% of the crossings and the most used bridge comprised 41% of our sample. Moreover, the most popular CS model had a high degree of stiffness, indicating that this material property may be a determinate of CS preference. On the other hand, the least popular model is less stiff or stable. Our findings provide a better understanding of CS design for nonhuman primates and may be incorporated into biological corridor management. This research was supported by the Riverbanks Conservation Support Fund.
Article
Gliding mammals are sensitive to habitat fragmentation that produces canopy gaps beyond their gliding capability. Specific structures (canopy-bridges and glide poles) are now commonly installed in large road construction projects to enable road crossing by threatened gliding mammals. However, these structures are being installed with limited understanding of how their design features influence their use. We conducted field testing of several design features (horizontal glide launch-beams at the top of poles; rope size and complexity in rope-bridges) using free-ranging gliding mammals, and scaled-down structures at two locations. Our aim was to identify preferred features to optimise structure use. This may confirm current designs or identify the need for refinement. We found that squirrel gliders (Petaurus norfolcensis) and sugar gliders (Petaurus breviceps) preferred a forward-pointing over a sideways-pointing glide beam. A single-rope rope-bridge was favoured over a mesh rope-bridge by sugar gliders but not squirrel gliders. No preference was shown by either species between mesh or ladder-style rope-bridges that differed in rope strand spacing. Large, permanently installed ladder or mesh rope-bridges commonly have single ropes connecting them to the adjacent forest. We investigated the use of a permanently installed 50-m long single-rope rope-bridge. Infra-red camera monitoring over 366 nights detected squirrel gliders on this bridge on 172 nights, common ringtail possums (Pseudocheirus peregrinus) on 144 nights and common brushtail possums (Trichosurus vulpecula) on 120 nights. This confirms acceptance of the single rope by a range of species and provides confidence in installing rope-bridges that may vary in rope size and complexity.
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Rope bridges are being increasingly installed worldwide to mitigate the negative impacts of roads on arboreal animals. However, monitoring of these structures is still limited and an assessment of factors influencing the crossing behaviours is lacking. We monitored the use of a rope bridge near Busselton, Western Australia by the endangered western ringtail possums (Pseudocheirus occidentalis) in order to identify the patterns of use and factors influencing the crossings. We installed motion sensor cameras and microchip readers on the bridge to record the crossings made by individual animals, and analysed these crossing data using generalised linear models that included factors such as days since the installation of the bridge, breeding season, wind speed, minimum temperature and moonlight. Possums started investigating the bridge even before the installation was completed, and the first complete crossing was recorded only 36 days after the installation, which is remarkably sooner than arboreal species studied in other parts of Australia. The possums crossed the bridge increasingly over 270 days of monitoring at a much higher rate than we expected (8.87 ± 0.59 complete crossings per night). Possums crossed the bridge less on windy nights and warm nights probably due to the risk of being blown away and heat stress on warmer days. Crossings also decreased slightly on brighter nights probably due to the higher risk of predation. Breeding season did not influence the crossings. Pseudocheirus occidentalis habituated to the bridge very quickly, and our results demonstrate that rope bridges have a potential as an effective mitigation measure against the negative impacts of roads on this species. More studies and longer monitoring, as well as investigating whether crossing results in the restoration of gene flow are then needed in order to further assess the true conservation value of these crossing structures.
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Context: Wildlife crossing structures are installed to mitigate the impacts of roads on animal populations, yet little is known about some aspects of their success. Many studies have monitored the use of structures by wildlife, but studies that also incorporate individual identification methods can offer additional insights into their effectiveness. Aims: We monitored the use of wildlife crossing structures by arboreal marsupials along the Hume Freeway in south-eastern Australia to (1) determine the species using these structures and their frequency of crossing, (2) determine the number and demographic characteristics of individuals crossing, and (3) use the rate of crossing by individuals to infer the types of movement that occurred. Methods: We used motion-triggered cameras to monitor five canopy bridges and 15 glider pole arrays installed at 13 sites along the Hume Freeway. The five canopy bridges were also monitored with passive integrated transponder (PIT)-tag readers to identify the rate of use by individuals. Key results: Five species of arboreal marsupial were detected using canopy bridges and glider poles at 11 sites. Our analysis suggested that increasing the number and the distance between poles in a glider pole array reduced the rate of use by squirrel gliders. The PIT tag and camera footage revealed that the structures were used by adult males, adult females and juveniles, suggesting that all demographic groups are capable of using canopy bridges and glider poles. At two canopy bridges, multiple squirrel gliders and common brushtail possums crossed more than once per night. Conclusions: Given that previous studies have shown that the freeway is a barrier to movement, and that many of the species detected crossing are subject to road mortality, we conclude that canopy bridges and glider poles benefit arboreal marsupials by providing safe access to resources that would otherwise be inaccessible. Implications: Although the factors influencing crossing rate require further study, our analysis suggests that glider pole arrays with fewer poles placed closer together are likely to be more successful for squirrel gliders. The individual identification methods applied here offer insights that are not possible from measuring the rate of use alone and should be adopted in future monitoring studies.
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The impact of time since fire after two consecutive wildfires 44 years apart (1939 and 1983) within the same area, and the distance from the fire boundary (<100 m or 500-2000 m), were investigated in relation to the distribution and abundance of arboreal marsupials in 1994. Arboreal marsupials were censused by stagwatching and spotlighting in two relatively young age classes of mountain ash (Eucalyptus regnans) dominated forest in the Central Highlands of Victoria. Five species of arboreal marsupial were detected, but only three were detected in sufficient numbers to determine habitat preferences. Petauroides volans (greater glider) was statistically more abundant in 1939 regrowth forests, while Trichosurus caninus (mountain brushtail possum) showed no significant preference for either age class of forest. All but one record of Gymnobelideus leadbeateri (Leadbeater's possum) came from young forest, though the effect of age-class was not statistically significant. Distance from fire boundary explained little or no variation in mammal distribution or abundance. While the actual number of hollow-bearing trees was similar in both age classes of forest, the long-term lifespan of hollow-bearing trees in more recently burnt forest is predicted to be lower than in unburnt or not recently burnt forest. Post-fire salvage logging following the 1983 wildfires appears to have reduced the number of hollow-bearing trees at sites burnt in 1983.
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We investigated the use of inexpensive aerial bridges (rope canopy bridges) above roads and a highway by arboreal mammals in the Wet Tropics of Queensland, Australia. Three rope bridge designs were trialed, including a single rope, ladder-like bridges and tunnel-shaped bridges. Nine mammal species were recorded using canopy bridges, including five species or subspecies endemic to the Wet Tropics and three species listed as rare under State nature conservation legislation. Most of these species suffer severely from either the fragmentation or mortality impacts caused by roads. Over 50 crossings above a 15-m-wide tourist road were observed on an elevated ladder-like bridge. Longer (∼40m) rope bridges were used on several occasions by four species. Our observations suggest that canopy bridges can assist rare arboreal mammals to cross roads in the Wet Tropics, thereby reducing both the risk of road-kill and the potential for subpopulation isolation. Further research is required to ascertain the level of benefit afforded by canopy bridges for arboreal mammal populations. It is likely that rope canopy bridges will have broad application for a range of arboreal mammal species.
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Wildlife crossing structures are commonly used to mitigate the barrier and mortality impacts of roads on wildlife. For arboreal mammals, canopy bridges, glider poles and vegetated medians are used to provide safe passage across roads. However, the effectiveness of these measures is unknown. We investigate the effect of canopy bridges, glider poles and vegetated medians on squirrel glider movement across a freeway in south-east Australia. We monitored structures directly using motion-triggered cameras and passive integrated transponder (PIT) scanners. Further, post-mitigation radio-tracking was compared to a pre-mitigation study. Squirrel gliders used all structure types to cross the freeway, while the unmitigated freeway remained a barrier to movement. However, movement was not restored to the levels observed at non-freeway sites. Nevertheless, based on the number and frequency of individuals crossing, mitigation is likely to provide some level of functional connectivity. The rate of crossing increased over several years as animals habituated to the structure. We also found that crossing rate can be a misleading indicator of effectiveness if the number of individuals crossing is not identified. Therefore, studies should employ long-term monitoring and identify individuals crossing if inferences about population connectivity are to be made from movement data alone.
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The geographic range of the squirrel glider (Petaurus norfolcensis) in south-eastern Australia largely corresponds with fertile soils highly suited for agriculture. As a consequence of extensive clearing for agriculture, the conservation of P. norfolcensis in south-eastern Australia is now reliant on a mosaic of many fragmented and isolated patches of woodland and forest. In this study, I investigated the population dynamics of P. norfolcensis in an agricultural landscape where most remnant woodland occurs as linear strips along roadsides, unused road reserves and watercourses. A total of 251 gliders were trapped 1343 times within the linear habitats between December 1996 and November 1998. Gliders were resident within the linear strips at 0.95–1.54 individuals ha–1, a density equal to, or greater than, that recorded elsewhere for the species in continuous forest. All adult females were reproductively active and the mean natality rate was 1.9 young per adult female per year. Overall, the population age-structure appeared to be stable. While currently supporting a stable, high-density population, the long-term viability of these remnants as habitat is not assured because roadside reserves are narrow, easily fragmented and subjected to a host of deleterious processes causing ongoing habitat loss and degradation.
Article
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A number of studies have proposed that wildlife passages beneath roads and railway lines might be exploited by mammalian predators as ‘prey-traps’ with prey-species being effectively funnelled into areas of high concentration. This proposition has raised the possibility that use of passages by predators may reduce the effectiveness of passages in conserving other forms of wildlife. We review the literature and conclude that evidence for the existence of prey-traps is scant, largely anecdotal and tends to indicate infrequent opportunism rather than the establishment of patterns of recurring predation. Most passage studies record no evidence of predation in or around passages. Conversely, there is some evidence that predator species use different passages than their prey.
Chapter
The potential for predators to use wildlife crossing structures for hunting could result in some species being preyed upon more frequently than elsewhere in the landscape. What would the consequences be if predators learn that hunting success is greater at wildlife crossing structures and develop preferences for these locations? Researchers and ecologists are frequently asked this question during the planning and design stages of road projects. Because there is no definitive answer to this question, the usual response is 'it depends', and the potential relevance of this situation should be assessed on a case-by-case basis. 1 Wildlife crossing structures will be less effective for prey if their use is adversely influenced by predator-prey interactions. 2 The outcome of predator-prey interactions at wildlife crossing structures may depend on the degree of co-evolution between them. 3 Our knowledge of specific interactions between predators and prey at crossing structures is scarce, and research is urgently needed. 4 Roads and crossing structures should be designed to minimise potentially deleterious predator-prey interactions. Altogether, the increased connectivity benefits provided by wildlife crossing structures for a wide range of species are positive, and the potential for predation should not be seen as a reason not to install such mitigation measures. The current evidence for predators using crossing structures in a systematic way to increase hunting effectiveness is scarce and controversial. However, the potential for such predation at or near crossing structures exists, and road planners and wildlife managers should aim to reduce this risk, particularly for rare species of prey.
Chapter
Global road length, number of vehicles and rate of per capita travel are high and predicted to increase significantly over the next few decades.2The ‘road-effect zone’ is a useful conceptual framework to quantify the negative ecological and environmental impacts of roads and traffic.3The effects of roads and traffic on wildlife are numerous, varied and typically deleterious.4The density and configuration of road networks are important considerations in road planning.5The costs to society of wildlife-vehicle collisions can be high.6The strategies of avoidance, minimisation, mitigation and offsetting are increasingly being adopted around the world – but it must be recognised that some impacts are unavoidable and unmitigable.7Road ecology is an applied science which underpins the quantification and mitigation of road impacts.
Chapter
Arboreal animals need trees for some or all of their shelter, food and movement. This diverse group of wildlife includes mammals, amphibians and reptiles that climb, crawl and glide in trees. Since trees are a critical resource, arboreal animals are directly affected by habitat loss from road construction. The susceptibility of arboreal animals to barrier effects and wildlife-vehicle collisions (WVC) will depend on their willingness, opportunity and ability to cross gaps. Methods to mitigate the impacts of roads and traffic are often unique and specific to this group of wildlife. 40.1 Always avoid clearing trees where possible. 40.2 Canopy connectivity is important for most arboreal animals. 40.3 Not all arboreal animals need arboreal crossing structures. 40.4 Further research on impacts and mitigation for arboreal species is needed. Recent studies have quantified the impacts of roads on some arboreal species, primarily mammals, and successful mitigation techniques are available. However, further research on the use and effectiveness of mitigation strategies for this group is urgently required, particularly for arboreal amphibians and reptiles.
Article
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.
Article
Tree‐dwelling mammals may be vulnerable to road mortality if forced to cross canopy gaps on the ground. This group of mammals has received scant attention worldwide despite major road projects potentially causing severe fragmentation to their habitat. Gliding mammals may be enabled to cross road gaps that exceed their gliding capability by the installation of tall wooden poles to act as “stepping stones.” We investigated whether such glide poles installed across two land‐bridges in eastern Australia could restore landscape connectivity for small gliding petaurid marsupials. Hair‐traps revealed repeated use of all poles at both locations over periods of 1–3 years. Camera traps at one site suggest a crossing frequency on the poles by the squirrel glider (Petaurus norfolcensis) of once every 3.8 nights. Radio‐tracked animals did not glide directly over the road but instead used the poles to cross on the bridge. Hair‐traps and camera traps installed within the middle of two reference land‐bridges that lacked glide poles failed to detect crossings by gliding mammals despite their presence in adjacent forest. These observations suggest that glide poles can facilitate road crossing and thereby restore habitat connectivity for gliding mammals. This lends support to the notion that glide poles have the potential to mitigate road‐induced habitat fragmentation for gliding mammals worldwide.
Article
A landscape approach was taken to modelling distributions of large forest owls and conserving habitat for them in 1.2 million ha of forest on the Great Dividing Range in north-east Victoria, south-eastern Australia. Owls were surveyed using call playback at 472 sites, selected by stratified random sampling from geographical information system (GIS) data. Habitat data were collected at each site and at four spatial scales from GIS data. Six owl species were recorded in or near the study region. Data on powerful owls (Ninox strenua) and sooty owls (Tyto tenebricosa) were modelled using logistic regression, and predicted probabilities of occurrence were mapped using GIS. Mapped variables explained more variation than habitat variables assessed at survey sites. Powerful owls were most likely to be observed at sites with mature dry forest, many live hollow-bearing trees, diverse habitats within 2 km, and not much pure regrowth within 5 km. Sooty owls were most likely to be observed at sites with wetter more senescent forest associated with tree-ferns (Cyathea australis and Dicksonia antarctica), blanket-leaf (Bedfordia arborescens) and silver wattles (Acacia dealbata), diverse habitats within 500 m and much senescent forest within 5 km. The models were field-tested and found to discriminate well between high and low probability sites. Actual records and then models were used to help select 225 protected areas for large owls, each of approximately 500 ha.
Article
This study describes the first attempt in the world to use timber poles to provide habitat connectivity for a gliding mammal. The Australian squirrel glider Petaurus norfolcensis is a small tree-dependent gliding marsupial whose habitat is characterized by ongoing fragmentation. We installed five 12 m-high poles across a 70 m gap that had existed between two woodland remnants for over 45 years. Our aims were to determine whether animals were able to use the poles for gliding and to travel between the remnants. We released 22 animals onto the poles at night. All animals readily climbed and glided from the poles. Five individuals successfully glided pole-to-pole on initial release. Squirrel gliders were captured in both remnants only after pole erection and two were trapped on poles. One radio-collared individual was observed gliding pole-to-pole to reach the non-home remnant where it foraged on two separate nights. Petaurus hair was detected on several poles by hair-sampling devices in four separate periods up to 12 months after radio-tracking and trapping had ceased. Our observations suggest that wooden poles may assist gliding mammals to traverse open areas between habitat patches and have the potential to be used as a rapid technique to reconnect severed habitat.
Barking owl, Ninox connivens. Department of Natural Resources and Environment
  • N Clemann
  • R Loyn
Clemann, N., and Loyn, R. (2001). Barking owl, Ninox connivens. Department of Natural Resources and Environment, No. 116, Melbourne.
1. Canopy bridge (a) and glider pole (b) to allow arboreal marsupials to cross the 208
  • Fig
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