The Fight Against Ferals

Bilbies can hold their own against natural predators like pythons, raptors, dingoes and quolls. But to give bilbies a fair chance of survival in the wild, it's vital to eliminate as many feral predators as possible before releases into the wild. While bilby burrows were always important as refuges for a range of natives- reptiles and other small marsupials, they are often taken over by rabbits and cats.

Released bilbies have spread well through the 13,000 hectare Dryandra Woodland in WA and seem to be coping with predators. Part of their success is due to a local plant which produces a selective poison which kills introduced animals, but not natives. Poison Bush occurs throughout the South-West and consequently native mammals are tolerant to the poison. The breeding program is going so well that more releases are planned around the South-West and up into the drier areas.

The Arid Recovery project in the harsh regions around Roxby Downs is trialling another innovative approach to the feral problem. After recently discovering that a group of bilbies released into the wild were killed by predators, they came up with the unusual idea of training the marsupials to avoid cats, with excellent results with bilbies in breeding programs.

"After training, bilbies that encountered cat scents and droppings changed their behaviour - hiding immediately, changing burrows more frequently and selecting burrows with more entrances - all activities that could assist them in avoiding predators," reports Katherine Moseby. "The next steps are to test it in the wild and see if parents can pass it on to their young."

Why are cats and foxes a problem in Australia?

Foxes were introduced into Australia soon after European settlement and are now well established over most of the non-tropical mainland. Foxes are incredibly resourceful and can survive on berries, insects or scavenged carrion in tough times, and in boom times they can hunt and feast on dozens native reptiles and small mammals in a single day.

They are very drought-tolerant and have thrived in desert Australia for over 70 years - preying mainly on rabbits up until Calici virus successfully decimated rabbit populations in the 1990s. Foxes are believed to have contributed to the mainland extinction of Mala, as well as tipping a number of native mammals such as Brush-tailed Bettongs, Black-footed Rock-wallabies, Golden Bandicoots and Western Quolls further toward extinction.

Cat arrival is believed to predate European settlement in Australia, with the first thought to have become established from shipwrecks off the coast of WA. Since then cats have invaded every environment in Australia, including many offshore islands. Cats feed on a huge range of live prey including birds, reptiles and small mammals.

In desert environments cats survive the extreme summer temperatures by sheltering in burrows dug by bilbies or dingoes, or by hiding in hollows in trees. Feral cats have been associated with the demise of a number of native animals including Numbats, Burrowing Bettongs, Bilbies and Malleefowl.

Bilby recruit (2nd generation of released captive-bred bilbies) set free after capture during a survey at Project Eden on Peron Peninsula, WA

Image Courtesy Kathy Himbeck / CALM WA

Why are they a threat to bilbies?

Cats and foxes successfully prey on both young and adult bilbies, particularly after large wildfire events when bilbies have to range further from home burrows to search for food. It is quite a sobering thing to be walking alongside Aboriginal people following the tracks of a bilby only to be shown tracks of a fox picking up the scent and trailing after the bilby. A little further along are the scuffle marks and the remains of fur or a forlorn tail-tip.

By looking for residual hair from native mammals in the scats of cats and foxes it is possible to measure the impact they are having on our native species. Recent research work in the Tanami Desert has shown bilby fur in roughly 3 percent of the cat scats examined. It seems remaining bilby populations in some desert areas are able to persist alongside fairly high levels of foxes and cats, probably as a result of favourable fire regimes in the region. These regimes can create enough high-quality food resources so bilbies do not need to spend long hours above ground looking for food.