Case study — Examples of trends in significant species and communities — south australia

Status of the greater bilby (Macrotis lagotis) within the Arid Recovery Reserve

Description

Arid Recovery is an ecosystem restoration program in the far north of South Australia. Now in its tenth year, the program is based around a 60 km2 reserve from which all feral cats, rabbits and foxes have been eradicated. An additional 26 km2 has recently been fenced and introduced species are being eradicated.

The reserve has created an area of complete protection allowing the regeneration of native flora and fauna and the successful re-introduction of four locally extinct mammal species, one of which is the greater bilby (Macrotis lagotis).

Figure 1. Location of Arid recovery Site in Northern South Australia

The greater bilby is a burrowing, nocturnal bandicoot that digs extensively for the seeds, bulbs and invertebrates that constitute its diet. The greater bilby has been successfully re-introduced to some areas and islands within its former range where feral cats and foxes are absent, intensively controlled or eradicated (e.g. Thistle Island in South Australia). Re-introductions into inland arid zone areas have proved more difficult due to the problems of controlling and excluding introduced predators from a large area without the use of peninsulas or costly fences. A trial re-introduction into Watarrka National Park in the Northern Territory failed due to high levels of predation (Southgate pers comm). Re-introduction research on bilbies in arid inland Australia has focused on spinifex deserts (e.g. Southgate 1990) and the potential success of bilby re-introductions into the chenopod shrublands and Acacia dunes of the southern arid zone was largely unknown.

Greater bilbies were known to previously inhabit the Arid Recovery area because sub-fossil material was collected 30 km from the reserve and local pastoralists remember ‘pinkies’, a colloquial name for bilbies, in the local sand dunes until the 1930s.

Significance

The greater bilby has declined since European settlement and although still found in the arid interior of the Northern Territory, Western Australia and Queensland, the species now occupies only 20 per cent of its former range (Pavey 2004). Current classifications list the bilby as vulnerable to extinction (Pavey 2004) and it is suggested that the bilby may still be in decline. Southgate et al. (1994) suggest that a combination of changing fire regimes, increased predation through the introduction of feral cats and foxes and degraded habitat caused by rabbits and stock was responsible for their historical decline.

Data and information

Bilbies are monitored at Arid Recovery through track transects, burrow monitoring, and quarterly capture using hand nets. Six track transects ranging from 3-10 km in length are conducted quarterly within the reserve and eight transects are conducted on the outside of the reserve. Between 20 and 30 bilby burrows are monitored annually for activity and 10 bilbies are captured by hand each quarter to compare body condition and reproductive output. Radio-tracking has also been conducted following internal and external bilby releases to gather information on survival, home range and habitat usage.

A number of research projects have contributed significant knowledge to the recovery effort. Key recent research at Arid Recovery includes: research on survival, ecology and reintroduction protocol (Moseby and O’Donnell 2000); foraging behaviour and influence of bilbies on the seed bank (James 2004, Newell 2004, James and Eldridge 2007), predator awareness training (Cameron 2005) and external bilby release (Cunningham 2004, Hill2004).

Management requirements and issues

Predation by feral cats and foxes is the main threat to the long-term survival of the greater bilby at Arid Recovery. The success of the greater bilby reintroduction at Arid Recovery is largely dependant on the ongoing exclusion or intensive management of such predators.

Other issues are intra-specific competition for resources within the Arid Recovery Reserve. With the absence of natural predation and limited opportunities for dispersal, animals inside fenced reserves will eventually become limited by resources. Significant population crashes of burrowing bettongs and brush-tailed bettongs have been experienced recently at other reserves in South Australia and Western Australia. Thus, ensuring the long term survival of bilbies in the arid zone should include protection of un-fenced large wild populations.

The long term impacts of restricting this wide-ranging and dispersing species in relatively small exclosures or ‘islands’ are unknown but large scale dispersal and movements may be important ecological processes that can only occur naturally in large tracts of available habitat.

Management actions and responses

The Arid Recovery Reserve has provided greater bilbies access to 52 km2 of feral cat and fox-free land through the use of a 1.8 metre high exclusion fence. Nine (5 female and 4 male) greater bilbies from the Monarto Zoo captive breeding facility were released into the Main Exclosure of the Arid Recovery Reserve in April 2000. In 2003, a further eight (4 males and 4 female) bilbies from Monarto were released into the Northern Expansion, while in 2004 15 (4 female and 11 male) bilbies from Thistle Island (SA) were released into the Northern Expansion and a further 10 were released from Monarto into the Northern Expansion in 2005. The total number of animals released to date is 42 (18 female and 24 male).

Arid Recovery is now attempting to support a sustainable population of greater bilbies in several ways by:

  • gradually expanding the Reserve to 119 km2 to facilitate dispersal and support a genetically viable population. A large reserve also increases the chance of patchy rainfall events falling inside the reserve, producing the ephemeral growth preferred by bilbies in their diet
  • reintroducing natural predators back into the environment (e.g. woma pythons) so that overpopulation may be controlled and a more balanced ecosystem produced
  • installing one-way gates to allow natural dispersal of bilbies outside the Reserve. In 2007 Arid Recovery tested four different one-way gate designs that would allow bilbies to disperse outside the reserve when numbers in the reserve are high, but would prevent any animals, including rabbits and feral predators, from invading. This would also contribute to our long-term goal of establishing viable populations of threatened species populations (i.e. bilbies) outside of the fenced reserve system
  • establishing a population of wild bilbies outside the reserve. In 2004 12 bilbies were released outside the Arid Recovery Reserve to determine if bilbies would survive in the wild. Unfortunately the majority of these were taken by feral cats within one month of release. However, some bilbies survived and bred over the following year, suggesting that some bilbies are able to survive in the presence of feral cats and foxes. The question then becomes ‘can bilbies learn to avoid feral cats and foxes?’ Subsequent research at Arid Recovery has identified that bilbies respond to predator-awareness training with trained bilbies exhibiting a heightened sense of awareness and responding to cat odour by moving burrows (Cameron 2005). Ten trained and untrained bilbies were released outside the reserve in 2007 to determine if survival is greater in bilbies that have been given predator awareness training. An intensive control program has also been undertaken outside the reserve to determine the level of predator control required for a population of wild bilbies to become established.

Outcomes

Greater bilby numbers have been fluctuating over the years in response to seasonal and local conditions (see Figure 2). Numbers often appear to be higher during the summer months and the population is estimated at between 300 and 500 individuals.

Figure 2. Number of greater bilby tracks per kilometre within the Main Exclosure (10km transect), First Expansion (5.5km transect) and Northern Expansion (16km transect) of the reserve. (Pink line denotes separation between different tracking methodologies).

During boom periods many bilbies are seen along the boundary fences, possibly trying to disperse. The release of the 10 captive-bred animals in 2005 failed possibly also due to overpopulation and an absence of free territories. The one-way gate trials (designed to allow bilbies to disperse outside the Reserve during periods of overpopulation) have identified that bilbies have a clear preference for a particular gate type that is different to the gates preferred by bettongs. The next stage of the trial is to test the gate types to determine if they will exclude predators.

The woma python release in 2007 was unsuccessful due to high predation by Mulga Snakes. Future research will look into using wild-caught woma pythons and also other potential natural predators that could be used to regulate bilby and other mammal populations in the reserve to create a more naturally functioning ecosystem.

The 2007 external bilby release has so far been very successful with both trained and untrained bilbies exhibiting high survival rates. The intensive predator control program is so far controlling feral cat and fox numbers to a level where both trained and untrained bilbies can survive. However, although pouch young have been recorded, no juvenile bilbies have been captured to date.

Future scenario

If expansion activities are funded, the greater bilby should eventually have access to more than 119 km2 of fenced arid zone habitat within the Arid Recovery Reserve. An additional 200 km2 of land adjacent to the Reserve will also be managed for greater bilbies by controlling feral cats and foxes. If predators can be effectively controlled outside the Reserve, then more than 300 km2 of land will be available for bilbies supporting up to 1000 individuals. One-way gates and native predators will be used to maintain population levels, prevent overcrowding and allow natural dispersal. Further research on broad-scale control of feral cats is urgently needed in order to protect extant bilby populations in the arid deserts. Arid Recovery is currently comparing aerial baiting with integrated control methods to develop a strategy for broad-scale control for the protection of threatened species such as the greater bilby.

Greater bilby – Photo: Hugh McGregor

References

Cameron A. 2005. A comparison of predator trained and untrained bilbies (Macrotislagotis). Arid Recovery Technical Report 2005 (1)

Cunningham L. 2004. A trial re-introduction of the Greater Bilby outside the Arid Recovery Reserve. Arid Recovery Technical Report 2004 (1)

Hill B. 2004. Outside bilby release. Arid Recovery Technical Report 2004 (3)

James A. 2004. The creation of fertile patches by four ecosystem engineers in an arid South Australian dunefield. Honours Thesis, UNSW.

James AI and Eldridge DJ. 2007. Reintroduction of fossorial native mammals and potential impacts on ecosystem processes in an Australian desert landscape, Biological Conservation , doi:10.1016/j.biocon.2007.04.029

Moseby KE and O'Donnell E. 2003. Reintroduction of the greater bilby, Macrotislagotis (Reid) (Marsupialia : Thylacomyidae), to northern South Australia: survival, ecology and notes on reintroduction protocol. Wildlife Research 30:15-27.

Newell J. 2004. Investigating the effects of ecosystem engineering by reintroduced Greater Bilbies (Macrotislagotis) and Burrowing Bettongs (Bettongialesueur). Poster presentation, Australasian Wildlife Management Society Conference, Kangaroo Island.

Pavey C. (2004). Recovery plan for the Greater Bilby, Macrotis lagotis, 2005-2010. Northern Territory Department of Infrastrucutre, Planning and Environment, Darwin.

Southgate RI. 1990. Distribution and abundance of the Greater Bilby, Macrotis lagotis Reid (Marsupialia:Peramelidae). In ‘Bandicoots and Bilbies’ (Eds J.H. Seebeck, P.R.Brown, R.I.Wallis and C.M. Kemper) pp 293-302. (Surrey Beaty and Sons: Sydney.)

Southgate RI, Bellchambers K, Romanow K. and Whitfield S. 1994. Re-introduction of the Greater Bilby, Volume 1 A field guide. Final Report to World Wide Fund for Nature, Project 95.

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Assessment of Australia’s Terrestrial Biodiversity 2008