News Archive

By Lindy Brophy

Possums in the south west are performing a high wire act every night.

But rather than being a death-defying feat, it is one that will save their lives.

The Western Ringtail Possum is a threatened species, as development - bringing roads, cars, people and cats - is contracting its habitat.

Animal biologist Roberta Bencini explained that roads were barriers to healthy genetic mixing. If a group of possums stayed in one spot, on one side of the road, they would become inbred, and their genetic diversity would become limited as they became isolated from other possums.

"This would result in animals that are not robust or able to cope with change, including environmental challenges such as global warming," Associate Professor Bencini said.

She and her PhD scholar Kaori Yokochi have had an eight metre high possum bridge built over Caves Road, Busselton, in the heart of a western ringtail possum hotspot.

The tree-dwelling marsupials don't move well on the ground so they either don't try to cross the road or get killed in the process.

The $10,000 steel wire and mesh bridge was sponsored by Main Roads WA and the Department of Parks and Wildlife (formerly Conservation and Environment).

"We know, from studies in the eastern states, that possums use rope bridges," Kaori said. "What we don't know is if the bridges aid the gene flow," she said.

Over the past few years, Kaori and Professor Bencini have fitted radio-collars to 70 possums in an area near the bridge and microchips in 238 possums. The collars have allowed them to track the possums.  Over 40 months, only three collared animals tried to cross Caves Road and two of them were killed.

The microchips are read by sensors at both sides of the bridge, which was opened to possum traffic in July.

"They started investigating it the first night," Kaori said. "From the photos taken by motion sensor cameras, we know there are several possums using the bridge, staying over the other side of the road for a few hours or longer and coming back.  And there have been no deaths on the road recorded."

Professor Bencini said young male possums needed to find their own territories; others were looking for mates, food or just exploring.

Kaori will be catching possums and taking DNA samples to estimate how many of young are sired by males from the other side of the road, and comparing numbers to see if breeding between separated groups has increased since the bridge was built.

"The outcome of this study will tell us if rope bridges truly prevent and reverse the negative impacts of road on possums," she said.

"This will give us a better understanding of the ways to minimise the impacts of road construction on our wildlife," Professor Bencini said.

They will monitor the possum traffic on the bridge until at least the end of the year.

"The western ringtail possum is an iconic species around Busselton and it is essential to ensure healthy populations of them can survive in the area," Kaori said.