Key words: fauna gates, feral proof fence
Bronwyn Merritt
The Southern Brown Bandicoot (SBB) Isoodon obesulus, once common along the coast from Sydney through to Adelaide, has dramatically declined in range and number since European settlement. Listed as an endangered species under the Environment Protection and Biodiversity Conservation Act 1999, SBBs are threatened by habitat loss, isolation, fragmentation, urban infrastructure and predation by introduced predators such as foxes.
The Royal Botanic Gardens Cranbourne (RBGC) is regarded as one of the most secure remnant populations of SBBs in the Melbourne and Western Port region. The persistence and relatively high abundance of the species at the RBGC can be attributed to ongoing integrated feral animal control, feral proof fencing and vegetation management.
The RBGC is 363 hectares, with approximately 250 hectares of remnant vegetation listed as of state conservation significance. The site is bounded by an 8 kilometre ‘floppy top’ feral proof fence that has been an integral part of the fox control program. It has resulted in ongoing reduced fox numbers and the flow-on of significant benefits for the management of SBB. However, the fence also represents a barrier to the movement of native species and this may affect the viability of populations within and outside the RBGC.
It has been observed that smaller SBBs are able to pass thorough the 50mm diamond mesh cyclone wire of the feral proof fence. This activity is probably sufficient to reduce local genetic isolation for the species. However, in places the fence has been reinforced with a second or third layer of wire skirting to reduce rabbit incursions and has, therefore, become less permeable to a range of native fauna.
The RBGC has an ongoing program trialing different methods to make the fence selectively permeable to some animals, whilst limiting the movement of others. Originally, the RBGC developed custom made gates that allowed the movement of Common Wombats (Vombatus ursinus) and Long-necked Tortoises (Chelodina longicollis). More recently, the RBGC has developed and trialed the use of ‘Bandicoot gates’ that have allowed free movement of the endangered SBB through the fenceline.
The custom designed bandicoot gates were installed in the internal Australian Garden fence of RBGC through 2010-2011. The Australian Garden is an 11 hectare display garden of native plants. The aim of the bandicoot gates was to allow the free movement of bandicoots, but exclude rabbits. The gates were made using 90 mm PVC pipe. Different gate versions were trialed and the successful design included a weighted 100mm wide flap and cover to ensure the gate returned to the closed position. The gates were monitored using Reconyx™ infra-red cameras and have shown frequent bandicoot movement, with no evidence of other species use to date.
The ability of the SBBs to learn how to negotiate the gates has ongoing implications for the construction of semi-permeable feral proof fences. It may be possible that these gates could be modified and used by other conservation reserves with feral proof fencing, for the conservation of other endangered small mammals.
For the RBGC, this has implications for allowing the free movement of the SBB into the wider region beyond the boundary of the perimeter fence. Since 2002, the land surrounding the RBGC has been included in the Melbourne Urban Growth Boundary, which means the RBGC is likely to be land-locked by residential development in the near future. The development of these gates, and the implication of allowing increased movement of SBB from the RBGC into proposed biolinks, will have significant implications for the ongoing management and sustainability of this endangered species.
Acknowledgements: Terry Coates, Ollie Sherlock, RBGC Infrastructure branch, Jill Burness, Dave Hunt and Ricardo Simao.
Contact: Bronwyn Merritt, Coordinator Land Management and Infrastructure, Royal Botanic Gardens Cranbourne, 1000 Ballarto Road, Cranbourne, Victoria 3977. Ph (03) 5990 2221. Bronwyn.merritt@rbg.vic.gov.au
EMR Project Summaries 