Underpasses Proven Beneficial for Wildlife

With more frequent and dangerous bushfires, floods, and ever-expanding cities, Australian wildlife have it rough these days. The threat of extinction is very real for some species, and the expansion of our road networks, especially highways, make life very dangerous. But recent research shows underpasses are a promising tool for minimising roadkill incidents.

Researchers from the Southern Cross University conducted a study over a period of two years, monitoring highway underpasses on the North Coast of NSW. They compared camera trap detection of animals in twelve underpasses – at Port Macquarie and Gosford – with footage from nearby forests.

Their findings were encouraging: almost 5,000 medium-large animals used their local underpass to safely cross highways. Lead researcher, Professor Ross Goldingay, called the numbers “quite astounding.” Species detected included several species of kangaroos and wallabies, goannas and pademelons, as well as smaller critters like bettongs and echidnas.

Larger animals, like eastern grey kangaroos and lace monitors, crossed some underpasses more than once a week. Smaller species, such as snakes and rodents, also used the tunnels, but were less reliably captured on camera.

Koalas were observed using underpasses only occasionally, but were also not detected very often in surrounding forests.

The ‘Prey-Trap’ Hypothesis

The study also looked at what is known as the ‘prey-trap’ hypothesis – the suggestion that underpasses make hunting easier for predators by funnelling animals into confined spaces. A few short-term studies have suggested foxes benefit unnaturally from underpasses in this way, and one study in Western Australia suggested a decline in bandicoot population was related to an underpass in the region.

However, SCU’s study did not observe results consistent with the hypothesis. “What we found was feral cats were very rare at both sites. We did have dingoes at both sites, but they weren’t very frequent in the underpasses, said Goldingay, “the red fox is the main concern, particularly in Port Macquarie.”

“However, the fox activity coincided less than expected with the activity of the mammals most at risk and it seemed potential prey were possibly avoiding using the underpasses when foxes were about.”

Estimates of roadkill tolls in Australia range from 10 to 20 million deaths per year. For some species, like the endangered cassowary in Queensland, being hit by a vehicle is the leading cause of death. Research like Goldingay’s is a positive reminder that we can – and must –  intervene to mitigate the destruction human civilisation brings to wildlife habitats.

In Tasmania – Australia’s roadkill capital – the government has trialled an app for people to report roadkill and try to target solutions to problem areas. Virtual fence posts are also being trialled in the state. These roadside devices emit light and sound when they sense a car approaching to warn animals away from the road. An average of 32 animals die every hour on Tasmanian roads.

“Underpasses are a useful generic tool to enable wildlife to move across landscapes with roads,” says Goldingay. Used in conjunction with other strategies, research shows they can help us reduce animal fatalities and take better care of our ecosystems.

Cover photo by David Clode on Unsplash.

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