![]() We also found foxes were less often detected on nights when potential prey were using the underpasses. But on average, there was a gap of over three hours between detecting foxes and bandicoots or pademelons, and over four hours between foxes and wallabies. We expected to detect foxes close in time to prey detection. Of the three underpasses used by foxes, one particularly favoured by foxes was not favoured by bandicoots and pademelons, the potential prey. At Port Macquarie, foxes were detected at three underpasses, while being absent from two. What we observed didn’t match these predictions. Even koalas were found to use underpasses. If the hypothesis was correct, foxes should be more common in the underpasses than in the forest, foxes should focus their activity at underpasses where potential prey are more abundant and the timing of use of underpasses by foxes and potential prey should coincide. We tested the prey-trap hypothesis by testing three predictions. But of these, only foxes were detected frequently enough to be a potential concern. ![]() We detected red foxes, feral cats and dingoes using these underpasses. This idea – known as the “ prey-trap hypothesis” – suggests predators will be drawn to places where they can easily pick off unsuspecting animals funnelled into the confined space of an underpass. ![]() Many people believe underpasses increase predator risk. Roadside fences develop holes and need to be repaired to maintain their value. Only four roadkills (two eastern grey kangaroos, one red-necked wallaby and one brushtail possum) were reported to the local animal welfare group for this road segment over a three year period encompassing our study. We found they were not avoiding the underpasses, because they were detected infrequently in the adjoining forest.ĭo underpasses with fences reduce or eliminate wildlife roadkill? Anecdotal evidence for our study road at Port Macquarie suggested roadkill rates were very low. We were particularly interested in whether the endangered koala would use the underpasses. Many animals made use of the underpasses, such as: (clockwise from left) rufous bettongs, lace monitors, red foxes and koalas. These crossing rates suggest animals use underpasses to forage on both sides of the freeways. Rufous bettongs and echidnas crossed individual underpasses every two to four weeks. Species such as eastern grey kangaroos, swamp wallabies, red-necked wallabies, red-necked pademelons and lace monitors crossed some underpasses more than once a week. We detected over 4,800 medium-large mammals and goannas, while smaller species such as snakes and rodents also used the underpasses but were less reliably detected by our cameras. Vastly more animals than we expected were using the underpass. Five under the Oxley Highway at Port Macquarie and seven under the Pacific Highway south of Grafton. To find out whether underpasses work, we used wildlife cameras to monitor 12 underpasses for more than two years in north-east New South Wales. ![]() A wildlife underpass at Port Macquarie, with fences used to funnel animals through it. We wanted to know if animals actually use underpasses – and if they had hidden dangers by funnelling animals through a confined space, making it easier for predators. Our new research explores whether highway underpasses help animals safely cross roads. But major roads become barriers to wildlife movement, as well as places where cars can hit and kill many animals. Governments expand our major highways in the interests of road safety and traffic flow. An associated factor is the expansion of our road network, particularly the upgrade and duplication of our highways. One key driver of this is habitat clearing and fragmentation. Australia’s wildlife is increasingly threatened with extinction.
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