By Dr Michael Smith, South-west Regional Ecologist, and Dr John Kanowski, Chief Science Officer
In 2015, Australian Wildlife Conservancy began an ambitious reintroduction project at Mt Gibson Wildlife Sanctuary, in south-west Western Australia. The sanctuary is located in the northern Wheatbelt, an area once rich in small and medium-sized native mammals. Based on sub-fossil evidence collected from the property, we believe more than 30 species historically inhabited the area, three of which are now globally extinct and another 13 are extinct from the region. AWC’s nationally significant reintroduction project aims to return at least 10 of the 13 regionally-extinct mammals back to Mt Gibson.
To date, eight mammal species have been reintroduced to a 7,800 hectare, fenced, feral predator-free area on the property: Numbats (Myrmecobius fasciatus), Red-tailed Phascogales (Phascogale calura), Western Barred Bandicoots (Perameles bougainville, also known in WA as Shark Bay Bandicoot), Greater Bilbies (Macrotis lagotis), Woylies (Bettongia penicillata), Banded Hare-wallabies (Lagostrophus fasciatus), Greater Stick-nest Rats (Leporillus conditor) and Shark Bay Mice (Pseudomys fieldi).This project has already set a new benchmark for rewilding projects in Australia; no other project has involved the return of so many regionally extinct species to one site.
The results are encouraging:
• Seven of the eight reintroduced species have fully established;
• Individuals are spreading across the fenced area; and
• There is evidence of breeding for some species. For example, Woylies – the first species to be reintroduced – have increased to more than 800 individuals over half the projected carrying capacity of the fenced area, after just four years.
Other threatened species, including Numbats and Bilbies, have expanded their range across most of the fenced area.
AWC plans to return the two remaining species – Western Quolls (Dasyurus geoffroii) and Brushtail Possums (Trichosurus vulpecula) – in the next few years. Of these, the Western Quoll (known as ‘Chuditch’ in Western Australia) is a top predator with a large home range. Quolls are expected to prey upon some reintroduced species, like bandicoots and rodents. While this is part of the natural process, populations of the potential prey species need to fully establish within the fenced area before being exposed to Quoll predation. For these reasons, Quolls may be better suited to release outside the fenced area than within it. Quolls are potentially capable of surviving outside the fenced area, in conjunction with feral animal control. Refugial populations of Western Quolls are known to persist in parts of south-western Australia subject to fox control, like at AWC’s Paruna Wildlife Sanctuary. Western Quolls have also been successfully reintroduced to other locations in WA and, more recently, to the Flinders Ranges in South Australia, where foxes and feral cats are suppressed.
To facilitate the Quoll reintroduction, AWC ecologists have been developing an ‘outside the fence’ strategy for Mt Gibson. The strategy draws on survey and statistical methods developed as part of research conducted by AWC at Scotia Wildlife Sanctuary and in the Pilliga State Conservation Area and Pilliga National Park in New South Wales. In 2019, AWC ecologists implemented the first stage of the strategy, deploying an array of 90 camera traps over 20,000 hectares of the broader landscape of Mt Gibson. Data from these cameras will be used to estimate the density of cats and foxes in the landscape.
Stage two of this strategy, to be undertaken in 2020, involves an aerial baiting program to drive down cat and fox densities. Data collected from camera trap arrays on the treated site, and from a matched control site, will be used to quantify the impacts of baiting. Provided baiting sufficiently suppresses fox and cat densities, AWC will progress to stage three – the reintroduction of quolls. Released animals will be monitored closely using satellite telemetry to assess their survival and movement. If successful, a larger release program will be enacted.
The planned reintroduction of Western Quolls to Mt Gibson is a major step towards re-establishing wildlife in WA’s Wheatbelt outside of fenced areas. A reduction in cat and fox densities will also benefit extant mammal fauna in the management area. AWC’s EcoHealth monitoring program at Mt Gibson will provide crucial data that will enable us to measure the ecological return for our investment on this exciting project.