The introduced red fox (Vulpes vulpes) has had a devastating impact of Australia’s native mammal fauna, particularly on those in the “Critical Weight Range”, between 35 and 5500 grams. Combined with landscape modification due to agricultural practices, changed fire regimes and other introduced species, many of these species have become extinct across much of mainland Australia.
An example of one of these species is the Woylie or Brush-tailed Bettong (Bettongia penicillata). With a former distribution covering large areas of arid and semi-arid Northern Territory, South Australia, New South Wales and Victoria, its natural occurring populations became restricted in the 1970s to three small wheatbelt reserves in Western Australia – Dryandra Woodland, and Tutanning and Perup Nature Reserves.
Woylies are members of the Family Potoridae, all small kangaroo-like marsupials under 3kg, formally known as “rat-kangaroos”. Woylies reach a maximum of 1850g, and are grey animals, with a dark brushy tail. They build basic nests on the ground in or near vegetation thickets, and their diet consists largely of fungi, tubers, bulbs, and seeds. They play an important ecological role through seed dispersal, and increasing soil and nutrient turnover with their diggings.
The woylie has shown some dramatic changes in conservation status. The IUCN listed the woylie as Endangered in 1982, due to its dramatic decline. A review of the conservation status of the woylie undertaken in 1998, lead to its status being downgraded on Western Australian, Australian and international threatened species lists, due to its apparent recovery in response to both fox baiting and reintroductions.
However in 2008, the woylie was again listed as Critically Endangered by the IUCN. This was due to a declining rate in numbers of 25-95% per annum since 2001, leading a 90% decline between 1999 and 2006. Estimations of total decline between 2001 and 2006 were around 70-80%, equating to 8,000-15,000 animals.
The main threats to the woylie were red foxes. One of the reasons they were able to survive in the three remaining reserve areas, was the presence of Gastrolobium plants, which contain monofluoroacetate, the compound present as sodium monofluoroacetate in “1080” toxic baits. These plants both protect the woylies with cover, as well as possibly causing reduction in predators due to secondary poison when the predators eat them.
The successful recovery during the 1980s and 1990s was largely due to intense fox baiting campaigns. Other causes of historical decline were loss of habitat from land clearing, grazing and changed fire regimes. Disease has also been suspected as an agent of decline.
The campaign of both intense fox bating and reintroduction into baited areas, and areas surrounded by predator proof fences was successful in the initial recovery of the woylie. From the initial three populations found in the 1970s, woylies were established in an additional 22 locations across Western Australia, South Australia and New South Wales.
As the recent causes of decline are unknown, it is difficult to plan actions for the woylie recovery. As with all declining species, additional research is essential to pinpoint causes of decline. As well as controlling foxes and cats, surveillance monitoring for diseases needs to continue.
The woylie is an example where continual research is needed on wildlife populations, even when we think they are in the clear. Without dedicated researchers, the extent of the recent decline of the woylie would have gone unnoticed. Without continual research-lead conservation of the woylie, the reasons for the decline will remain a mystery.
The Conversation is running a series on Australian endangered species. See it here.