By Dr John Kanowski, Chief Science Officer
Over the past two centuries, large areas of Australia have lost most of their small to medium-sized native mammals: carnivorous marsupials, Bilbies, bettongs, bandicoots, small wallabies and native rodents. This hollowing out of our mammal fauna represents a major loss of our natural and cultural heritage, and a part of our national identity.
No other nation has faced such an extinction crisis: 10 per cent of Australian mammals have gone extinct and another 20 per cent are threatened, with predation by feral cats and foxes a primary driver of these extinctions and declines.
The consequences for conservation extend beyond the loss of species to the disruption of the ecological processes in which the lost mammals participate – soil engineering (digging for food and shelter), spore and seed dispersal, herbivory and predation.
Establishing a network of feral-free areas
For over a century, and increasingly in recent decades, Australian ecologists have made attempts to re-establish populations of locally- extinct mammals at sites within their former ranges. These projects have been undertaken by private individuals, government agencies and conservation organisations. AWC began its reintroduction program over 25 years ago, when our founder, Martin Copley, fenced foxes and feral cats out of Karakamia Wildlife Sanctuary in the hills, east of Perth, Western Australia, and reintroduced Brush-tailed Bettongs (Woylies) and several other threatened species.
Since then, AWC has established a national network of reintroduction projects, including one island (Faure Island, WA), and seven fenced ‘mainland islands’: Karakamia and Mt Gibson Wildlife Sanctuaries in WA, Newhaven Wildlife Sanctuary in the Northern Territory, Yookamurra Wildlife Sanctuary in South Australia, and in New South Wales at Scotia Wildlife Sanctuary, and the Pilliga State Conservation Area and Mallee Cliffs National Park, in partnership with the NSW Government.
Feral cats and foxes have been eliminated from these reintroduction sites. AWC also conducts reintroduction programs at two sites where feral predators are controlled, but not excluded, by fences: Paruna Wildlife Sanctuary, in WA, and North Head, in NSW, in partnership with Sydney Harbour Federation Trust.
Restoring threatened wildlife populations
AWC’s reintroduction projects support, in total, a dozen nationally- threatened mammal species. For some species, like the Bridled Nailtail Wallaby, Greater Bilby, Burrowing Bettong, Mala and Numbat, the populations in AWC’s reintroduction program represent a substantial proportion of individuals remaining on the planet. AWC plans to reintroduce additional species to the network in the next few years, including endangered mammals, such as the Central Rock Rat and Northern Bettong, that are not currently represented in any secure (i.e., feral predator-free) area.
As well as threatened species, AWC’s reintroduction projects support a range of locally-extinct mammal species, for example, the Eastern Pygmy Possum, Brown Antechinus and Bush Rat have been reintroduced to North Head. None of these species are nationally threatened – they were all originally part of the North Head ecosystem – and their return is as much part of looking after the bush as removing weeds or implementing ecologically- appropriate fire regimes. For the same reason, AWC has reintroduced the Common Brushtail Possum to Yookamurra and Karakamia, and we plan to return this species to Mt Gibson and Newhaven in coming years.
Research conducted by AWC has shown the exclusion of feral predators from fenced reintroduction sites has other benefits for wildlife. At Scotia, analysis of long-term trapping data has shown populations of native mammals are generally higher inside the fenced area than outside:
Similarly, since construction of the fence at Mt Gibson, analysis of bird survey data has shown some birds are recorded more frequently inside the fence than outside (Smith et al. 2020).
Other work in progress indicates ground-active birds are particularly advantaged by the exclusion of feral predators. There are, for example, higher levels of active Malleefowl nest mounds inside the fenced areas at Scotia and Mt Gibson than outside where foxes and cats persist.
Measuring, monitoring and refining our approach
In conjunction with our reintroduction program, AWC ecologists conduct a suite of monitoring and research projects aimed at documenting the outcomes of reintroductions, improving our knowledge of reintroduction techniques, and enhancing our understanding of the ecology of threatened mammals and the ecological processes in which they participate.
Reintroduced animals are monitored using radio-telemetry, live-trapping, cameras and observational surveys. Extant fauna are monitored using trapping and observational surveys, while vegetation is monitored on plots inside and outside fenced areas.
At Mt Gibson, surveys have shown seven of the eight species of mammals reintroduced since 2015 have increased in population size or expanded their range since release within the fenced area.The population of Woylies has grown to over 1,000 individuals – large enough to support harvests for other reintroduction projects. Research has compared outcomes for Numbats sourced from wild and captive-bred populations, with important lessons for future reintroduction projects (e.g., Palmer et al. 2020).
A key strength of AWC’s research is that our field ecologists who conduct the reintroductions are the same people who undertake the research, ensuring the work is tightly focused on issues of applied conservation relevance.
In addition to the conservation and research outcomes, AWC’s reintroduction program has provided opportunities for engagement with Traditional Owners, who have been involved in ‘Welcome to Country’ ceremonies, releases of reintroduced species, and ranger work on a number of projects. The broader community has also been involved through public education events.
Palmer N, Smith M, Ruykys L, Jackson C, Volck G, Riessen N, Thomasz A, Moir C, Palmer B (2020) Wild-born versus captive-bred: a comparison of survival and refuge selection by translocated numbats (Myrmecobius fasciatus). Wildlife Research (in press).
Roshier DA, L’Hotellier F, Carter A, Kemp L, Potts JM, Hayward MW, Legge SM (2020) Long-term benefits and short-term costs: small vertebrate responses to predator exclusion and native mammal reintroductions in south-west NSW, Australia. Wildlife Research (in press).
Smith MJ, Ruykys L, Palmer B, Palmer N, Volck G, Thomasz A, Riessen N (2020) The impact of a fox- and cat free safe haven on the bird fauna of remnant vegetation in south-western Australia. Restoration Ecology 28, 468-474