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Wildlife uses motorway underpasses, Southern Cross University study reveals

Written by Javed Iqbal

Have you ever driven past special wildlife crossings and wondered if they actually work?

There is new evidence to suggest they are effective, based on the first long-term study of underpasses in Australia.

The research from Southern Cross University (SCU) was published in the journal Ecology and Evolution and was based on a two-year study of underpasses located on the Mid North Coast of New South Wales.

During that time, wildlife cameras detected close to 5,000 medium to large mammals and goannas using highway underpasses at Port Macquarie and Grafton.

The researchers examined 12 underpasses in these two areas – five under the Oxley Highway at Port Macquarie and seven under the Pacific Highway south of Grafton – and compared camera trap records of animals at underpasses with those at nearby forest sites.

A koala at night walking through a motorway underpass
A koala has been caught on camera using a motorway underpass on the Mid North Coast.(Provided by: Southern Cross University)

Lead researcher SCU Associate Professor Ross Goldingay said the findings were encouraging.

“More than 4,800 detections were made; that number was quite astonishing,” he said.

“These crossing speeds suggest that animals used the underpasses to forage on both sides of the highways.”

Associate Professor Goldingay said certain species including eastern gray kangaroos, swamp wallabies, red-necked wallabies, red-necked pademelons and lace monitors crossed some underpasses more than once a week.

A road underpass with trees in the background.
A dedicated wildlife underpass at Port Macquarie where there have been regular animal sightings.(Provided by: Southern Cross University)

“We actually got quite a bit of traffic of animals passing through these underpasses, particularly in Port Macquarie … it’s a wetter forest type there so it seems there’s a greater abundance of animals,” he said.

“We got eastern gray kangaroos and swamp wallabies moving through two to four times a week and other species, including the red-necked pademelon, were coming through once every two weeks, so quite often.

“At Grafton we have a very large use of a couple of subs of echidnas and another small wallaby called the russet bettong, which is actually a NSW-listed threatened species.”

Concerns about the ‘prey trap’ dismissed

The study also allayed concerns that underpasses could become a “prey trap” used by introduced wildlife pests and that animals could be trapped in the relatively confined area.

A cute reddish bettong, a small gray furry animal that looks like a cross between a wallaby and a rat.
The marsupial bettong is a small, nocturnal marsupial species that has been seen using the underpasses.(Delivered: Mt Rothwell)

“We looked at it in detail as there have been a couple of other short-term studies where they’ve had frequent occurrences of foxes in a few underpasses, and in one case in Western Australia, which coincided with a decline in bandicoots using just that. understudy,” Professor Goldingay.

“Because we had more subjects and a longer period of time for this study, we were able to look at this in more detail than anyone has before.”

Professor Goldingay said predators discovered at the underpasses included the introduced red fox, feral cat and dingo.

“What we found was that feral cats were very rare at both sites. We had dingoes at both sites, but they were not very frequent in the underpasses,” he said.

“The reed fox is the biggest concern, particularly in Port Macquarie. Of the five underpasses there, three were used relatively frequently.

“However, fox activity coincided less than expected with the activity of the mammals most at risk, and it appeared that potential prey may have avoided using the underpasses when the foxes were around.”

Caution is still necessary

A concrete underpass tunnel for the motorway.
A combined wildlife and drainage underpass at Grafton.(Provided by: Southern Cross University)

Despite the positive survey results, Professor Goldingay said any expansion of the road network in Australia still needed to be done with caution.

“Australia’s wildlife species are increasingly threatened by extinction, habitat clearing and fragmentation,” he said.

“A main reason for this is the expansion of our road network, particularly the upgrading and duplication of major motorways.

“Underpasses are a useful generic tool for enabling wildlife to move across road landscapes. However, not all terrestrial animal species will find underpasses to their liking, but so far many do.”

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Javed Iqbal

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