Yellow-footed rock-wallaby recovery in the Flinders and Olary Ranges, South Australia
The yellow-footed rock-wallaby was historically widespread across inland areas of South Australia, New South Wales and Queensland. There are two distinct subspecies currently recognised: Petrogale xanthopus xanthopus in South Australia and New South Wales, and P. x. celeris in Queensland. In South Australia, the yellow-footed rock-wallaby has a naturally fragmented distribution with three major clusters of populations occurring in the Gawler Ranges, Flinders Ranges and west of the Olary Hills (Lim et al 1987, Copley and Alexander 1997, see Figure 1).
Yellow-footed Rock-wallabies are found in groups of up to several dozen individuals (Lim 1987) and a number of such groups, each on separate aggregations of rock piles, form a colony. Colonies are often separated by large expanses of unsuitable habitat (Lim et al 1992).
Like many other arid zone mammals, yellow-footed rock-wallaby populations can fluctuate greatly depending on seasonal conditions with marked increases after good rainfall events and declines during drought. They are more sensitive to the influence of drought than larger kangaroo species, probably because of their smaller home-range and specialised habitat requirements.
Suitable habitat for the yellow-footed rock-wallaby consists of rocky outcrops, cliffs and ridges in arid and semi-arid country (Copley 1983, Lim et al 1987). These rocky outcrops provide shelter sites that enable the wallabies to escape extreme climatic conditions and refuge from predators. Further, the steep slopes and narrow gullies (particularly those orientated north-south) provide shade and shelter for much of the day and lead to a milder micro-climate compared to surrounding areas with reduced temperature extremes, higher relative humidity and lessened evaporative water loss. These factors influence the vegetation that occurs in such areas, with preferred habitat supporting more diverse vegetation than the surrounding plains (Wilson 1976).
The importance of permanent fresh water for continued survival of the Yellow-footed Rock–wallaby is not clear. In some areas colonies can persist with access to only small soaks at the edges of rock faces while others rely on permanent springs. High numbers of introduced and native grazers can also be attracted to these permanent water-points that can lead to fouling of the water source and grazing impact on the surrounding vegetation.
Figure 1: Distribution of the yellow-footed rock-wallaby in South Australia.
Yellow-footed rock-wallaby populations are a focus for recovery for the Bounceback ecological restoration program that has been operating in the Flinders and Olary Ranges of South Australia since the early 1990’s and more recently extended to the Gawler Ranges. Yellow-footed rock-wallaby protection emerged as a priority due to high risk of local population extinctions and limited chance of recovery without active intervention.
The yellow-footed rock-wallaby is listed as vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and the South Australian National Parks and Wildlife Act 1972. This rating is based on IUCN criteria with respect to the total population size of the South Australian subspecies that is now estimated at about 10 000 animals (Lim et al 1992, South Australia Recovery Plan 2007).
Since European settlement the yellow-footed rock-wallaby has declined dramatically in distribution and abundance, with several colonies in South Australia becoming extinct as recently as 1981. Their decline can be attributed to a number of factors including over-exploitation by shooters for their skins during the 1880s - 1920s, predation by introduced red foxes Vulpes vulpes, and competition from introduced herbivores, particularly feral goats Capra hircus and rabbits Oryctolagus cuniculus (Copley 1983, Lim et al 1987). In other parts of South Australia their decline has been even more dramatic with less than five colonies currently known from the western Gawler Ranges and seven in the Olary Ranges.
Data and information
Historical evidence from across the species range suggests that the yellow-footed rock-wallaby was more abundant and widely distributed than they are today. European settlers arriving in the Flinders Ranges in the 1860’s reported seeing ‘small droves of forty or fifty’ animals, however such numbers are no longer seen. Despite this decline, ground-based surveys in the early 1980s (Copley 1983) and 2000-2002 (Lethbridge 2002) recorded approximately two hundred colonies throughout the Flinders Ranges from Telowie Gorge in the south to Brindana Gorge in the north. These surveys showed that, although the species has maintained its historic range, a number of local colony extinctions have occurred since the 1970’s.
Since the early 1980’s, aerial surveys have been conducted in key areas of the species’ range in South Australia to monitor population trends. Ground-based trapping programs have also been conducted at a number of colonies in South Australia to supplement the broad scale aerial surveys and investigate population parameters such as fecundity and survival. Tissue samples have also been collected for genetic analysis as part of the trapping program and provide important information for management of the species.
Despite nearly three decades of study directed towards the yellow-footed rock-wallaby there are still many gaps in our knowledge in terms of fully understanding the ecology and population dynamics of the species. There are currently a number of research projects underway in South Australia to address these gaps including a study to investigate whether fox predation limits or regulates rock-wallaby populations and another investigating the impact of total grazing pressure on food resources and habitat quality for the yellow-footed rock-wallaby. Further studies are also needed to better understand factors such how far individual animals disperse to find suitable habitat and what environmental factors trigger such dispersal. None of these basic ecological questions are well understood and are extremely important issues for ongoing management of the species across its range.
Management requirements and issues
The most significant threat for the yellow-footed rock-wallaby is predation by foxes, particularly of juveniles. Competition for food resources, mainly with goats but also with rabbits, sheep and possibly Euros, can be particularly detrimental in dry years. Habitat modification due to grazing and browsing by introduced herbivores also impacts on the species. Competition from feral goats for caves used to shelter from the heat is also considered to be a threat. In some parts of their range, small population numbers means that they are at extreme risk of localised catastrophic events such as wildfire and may also experience problems associated with low genetic variability.
Population viability modelling for the species indicates that emerging threats such as climate change and the predicted decline in rainfall will have a significant effect on the long term persistence of colonies in key areas of the species range (Lethbridge and Alexander 2008).
Management actions and responses
Current threat abatement works include broad scale goat control and fox baiting programs in the National Park Reserves and selected private landholdings. Tens of thousands of feral goats have been removed since 1992 and thousands of square kilometres of habitat have received fox control. These activities, designed to promote a recovery response in the wallaby populations, have occurred on reserves and on pastoral leases with the cooperation of landholders under the Bounceback project.
A Recovery Plan is currently under development for the yellow-footed rock-wallaby in South Australia to assist in prioritising areas for future management and monitoring.
Partners with the Department for Environment and Heritage in Bounceback include: the Australian Government’s Natural Heritage Trust / the South Australian Arid Lands Natural Resource Management Board, landholders, the local community, Flinders University, Adelaide Zoo, the Hunting and Conservation Branch of the Sporting Shooters Association of Australia, The yellow-footed rock-wallaby Preservation Association, Conservation Volunteers Australia, Warraweena Conservation Reserve, Arkaroola Sanctuary and Bunkers Conservation Reserve. Bounceback is also supporting Adelaide Zoo in their captive release of yellow-footed rock-wallaby into the Aroona Sanctuary at Leigh Creek through feral animal control assistance.
The yellow-footed rock-wallaby is known to occur within a number of conservation areas within South Australia including: the Flinders Ranges National Park, the Vulkathunha – Gammon Ranges National Park, Mt. Remarkable National Park, Gawler Ranges National Park, Dutchman’s Stern Conservation Park, Telowie Gorge Conservation Park, Bimbowrie Conservation Reserve and Bunkers Conservation Reserve. They are also known to occur on a number of pastoral leases, private sanctuaries and Indigenous Protected Areas within northern South Australia.
Results from aerial surveys indicate that numbers of yellow-footed rock-wallaby have increased from very low levels in the Flinders Ranges National Park and in landholdings in the Olary Ranges where threat abatement programs are in place. Of particular importance is the species response to drought-induced population declines in such areas with the rate of recovery greater where active goat and fox control programs are in place compared to those where no or limited threat abatement programs are conducted.
Population monitoring is conducted via annual aerial surveys. In the Flinders Ranges National Park, the population was estimated to be less than 30 in 1993. In 2007, following dry conditions over the previous 2 years, the estimate was approaching 800 animals. In the Olary Ranges, the population has increased from less than 50 in 1993 to approaching 1000 in 2007. The response in the Olary Ranges demonstrates that pastoralism can work effectively with conservation.
The aerial and ground-based surveys have shown that the active management of Rock-wallaby populations has significantly increased their viability throughout South Australia, preventing key populations from returning to the dangerously low levels that were observed in the early 1990's. This is particularly significant given that populations are remaining viable even during the current drought conditions.
Longer-term measures of the effectiveness of the threat abatement work conducted by Bounceback are to achieve a down-listing under the EPBC Act from Vulnerable to Conservation Dependent but this will depend on a large number of factors, some that can be planned for and others that are beyond our current level of control.
Long-term commitment to feral animal control programs will require long term funding for such operations that is not always possible within the short-term funding cycles available for nature conservation-related programs. New and innovative ways to attract funding for such programs and assist landholders in managing their properties for biodiversity outcomes is required and is an area currently being investigated.
The impact of climate change on the recovery of yellow-footed rock-wallaby populations is more difficult to deal with due to the uncertainty of predicted environmental changes. Decreases in annual rainfall and increased occurrence of drought conditions and risk of wildfire will certainly impact on the long-term recovery of the species. In terms of management, a better understanding of the ecology of the yellow-footed rock-wallaby will assist in managing for the species recovery in the context of uncertain changes to the environment.
Yellow-footed rock-wallaby. Photo Lynn Pedler
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