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Hume Highway Wildlife Overpass

On a Saturday in June 2007, traffic on the busy Hume Highway near Benalla was diverted for an unusual reason. The first of three rope bridges and three 'glider poles' were being installed to provide a means for squirrel gliders, possums and other native animals to pass safely across the road. The bridge and poles, the first of their kind in Victoria, were the culmination of a three-year research program involving researchers from the ARCUE, Monash University, the University of Melbourne and VicRoads.

The rope bridge and glider poles were mainly installed for the Squirrel Glider, a species threatened with extinction in Victoria and New South Wales. These animals move by gliding from tree to tree; where there are large gaps in tree cover, such as major roads, they are unable to safely cross. Dr Rodney van der Ree, Senior Ecologist at ARCUE, explains why this is of concern to researchers: 'It is crucial to encourage movement of animals across roads and among squirrel glider populations so that they can access food, shelter and mates. What appears to be happening is that those squirrel gliders who are on opposite sides of the highway are effectively different groups. Despite being just 100 metres apart, they might as well be one kilometre or ten kilometres apart. They have become cut off from the rest of their group and we are fearful that this could lead to local extinction.'

But this is not merely a local problem. The loss and fragmentation of natural habitat is considered one of the primary threats to the conservation of biological diversity around the world. Roads in particular are a major cause of habitat loss and fragmentation. They have been shown to reduce the quality of nearby habitats, with some effects extending for hundreds or thousands of metres from the road. One of the most obvious examples of the negative effect of traffic is the high rate of animal deaths resulting from collisions with motor vehicles.

The inability of animals to cross the road, due to either high mortality rates or avoidance of the unsuitable habitat, results in the creation of a barrier that prevents or limits animal movement. To reduce the barrier effect, roads can be located in areas that are less environmentally sensitive. However in many instances, opportunities to re-route roads are limited and in these situations, roads may be designed with engineering solutions to facilitate the safe-crossing by wildlife. The most common measures are tunnels or culverts that enable wildlife to pass under the road, or 'eco-bridges' that direct animals over the road.

Researchers on the Hume Highway project concentrated on finding out how, where and why animals cross the busy freeway. Rodney points out that, as a result, 'The world’s ecologists are watching this program closely because we have a good understanding about what has happened before an animal-only overpass has been built.'

Interest in such purpose-built structures is increasing in Australia and internationally, and, as Rodney says, 'This project puts Australia at the forefront of international efforts to determine how effective structures, such as overpasses, culverts and pipes really are in enabling animals to move more easily.'

Meanwhile the use by wildlife of the new bridges and poles will be monitored by ARCUE and Monash University PhD student Silvana Cesarini, and the information gained will be used in planning future road projects.

Preliminary Results

After one year of monitoring, it appears that possums and gliders are adapting to this new crossing structure.

Cameras have recorded:

• 50 ringtail possum crossings, and 50 partial crossings by ringtails
• Seven partial crossings by brushtail possums
• Four partial crossings by Squirrel Gliders

It is expected that over time animals will become less wary of the crossing structure and more likely to make a complete crossing.

See also: Wildlife Overpass in the Media