Threatened Species - Reintroducing the Bilby to South Australia

• Bilby Profile
• The Decline
• Bringing the Bilby Back to South Australia
• Release Procedure
• Population Monitoring
• Results
• Overcoming Problems
• Into the Future
• Program Support
• Author / Contact

Bilby (Photo: J van Weenen)

Bilby Profile

• Scientific name: Macrotis lagotis
• Common names: Greater Bilby, Rabbit-eared Bandicoot, pinki, dalgyte, ninu and walpa
• They are sexually dimorphic with males growing larger than females: males = 1.5 to 2.5 kg, females = 0.8 to 1.2 kg
• Bilbies are omnivorous, feeding on invertebrates, fungi, seeds, bulbs and occasionally small vertebrates
• They use burrows to avoid temperature extremes and predators

The Decline

Bilbies used to cover about 70% of the Australian mainland. Threats associated with European settlement (eg introduction of new predators/competitors and land clearance) have resulted in their dramatic decline and they now only cover approximately 20% of their former range. Bilbies have been extinct in South Australia since around the 1930s.

Bringing the Bilby Back to South Australia

As South Australia forms a large part of the bilby's former range, an important component of the bilby's recovery is its reintroduction to this state. In 1994, the South Australian Bilby Recovery Team was formed to coordinate the recovery of this unique animal in South Australia. A recovery program was developed for reintroducing the bilby to South Australia and this involved three main steps:

Bilby holding pen (Photo: J van Weenen)

1. Establish a captive colony in South Australia
2. Using captive animals, establish a self sustaining wild population
3. Utilise the wild population to provide animals for reintroductions to other parts of its range

A captive bilby colony was established at the South Australian Department for Environment and Heritage's breeding facility at Monarto in 1994. Successful captive breeding has enabled the South Australia Bilby Recovery Team to proceed to 'Stage 2' and trial the establishment of a self-sustaining wild population. An offshore island in Spencer Gulf was chosen for 'Stage 2' of the recovery program for 2 main reasons. Importantly, the island was of sufficient size to support a viable bilby population. It was also the largest parcel of land in South Australia that was both within the bilby's former range and free of foxes, cats and rabbits.

Release Procedure

Roadside bilby diggings (Photo:J van Weenen)

• When taken to the release site, bilbies are placed separately into small yards to ensure each digs their own burrow
• Each individual is provided with food/water and held in their pen for a period of 1-2 nights
• When released from their pens, individuals are given access to a 50 m x 50 m yard for a month
• The yard allows animals to interact with each other and get used to the natural vegetation and foods
• When released from the yard, animals then are able to roam free
• The bilbies are provided with food/water for a month after their release from the yard (to help keep them in the release area) and then are left to find wild foods
• This photograph shows where bilbies have been digging for bulbs along the edge of a track on an off shore island

Population Monitoring

Since the island release trials began in 1997, the population has been closely monitored to understand better the reasons for any failure or success. By recapturing animals it has been possible to check their condition over time and assess how they are coping with their new surroundings. Positive results obtained from the monitoring to date suggest this island introduction is likely to be a success.

The graph shows the data obtained from the regular catch up of the six animals released to the island and the growth of island born young. Males (M) were found to lose condition over summer whilst females (F) have remained in good condition since their release. Female weight fluctuations tend to reflect the growth and emergence of pouch young. Pouch young were weaned at similar weights to those observed in captivity and the juveniles have experienced good growth rates.

Results

• Within 24 months of the release onto the island, bilby signs were visible over approximately one third (13 km²) of the island
• It is possible to find areas on the island that bilbies have visited in the past but have since vacated
• The population estimate for the bilbies on the island is between 25-40 individuals
• In 5-10 years, it is hoped that the bilby population should be large enough to enable the capture and movement of individuals to other sites

Radio transmitter attached to bilby tail (Photo: J van Weenen)

Overcoming Problems

• During December 1997, the trial introduction of bilbies to an offshore island experienced a significant setback, with bilby radio-collars (used to monitor the movements and condition of individuals) being linked to the death of three of the four animals released
• To overcome the collar problem, new tail-transmitters were developed and trialled. These new transmitters enabled the successful tracking of all animals subsequently released

Into the Future

With a successful captive breeding program and the positive results being obtained from the island program, the Bilby Recovery Team has been able to provide animals for trial release exercises at other sites. South Australian bilbies have already been sent to Western Australia to assist in other recovery programs and in April 2000, bilbies were also reintroduced to the Arid Recovery site near Roxby Downs (where they are currently doing well). Intensive threat mitigation programs at sites like Venus Bay Conservation Park, Flinders Ranges National Park and Lincoln/Coffin Bay National Parks, means that further reintroduction trials should soon be possible.

Program Support

• Natural Heritage Trust
• Nature Foundation SA
• Adelaide Zoo
• Monarto Zoological Park
• Ark on Eyre
• Arid Recovery
• Landowners of the "island"

Author / Contact

Jasonvan Weenen, Scientific Officer, Threatened Species, Department for Environment and Heritage