Behavioural ecology of the black-flanked rock-wallaby (Petrogale lateralis lateralis): Refuge importance in a variable environment
The black-flanked rock-wallaby (Petrogale lateralis lateralis) has suffered a significant decline in its distribution in Western Australia. This has been attributed to introduced predators (predominantly the red fox) and herbivores, fire, and habitat destruction due to clearing. Although since 2001 the Department of Environment and Conservation (DEC) had begun to reintroduce this species back into its former range, little was known of the behavioural ecology of this species. Fox control in the 1980s and 1990s resulted in population increases of rock-wallabies on several reserves in the central wheatbelt of WA. However, recently these populations have rapidly declined despite continuing fox control. All too often, management and conservation programs are based on little understanding on the natural history and ecology of animals, which can ultimately result in poor management. One of the major problems with our understanding of the ecology of P. l. lateralis was that there was little information on their behavioural, foraging and feeding patterns, and how these affect the population dynamics of the species. Although this species appears to be substrate bound, requiring complex rock structures that are believed to protect them from both predators and adverse climatic conditions, there was still little understanding of how these animals utilise this important resource, particularly in highly variable environments. There is a long-standing premise in behavioural ecology that highly variable environments can significantly affect the behaviour and demography of animal populations. Although this has been well documented in birds, and primates, behavioural elements are rarely incorporated into marsupial studies. For the success of any current and future reintroductions of rock- wallaby populations into new areas, we needed to understand the relationships between the landscape and climatic elements and the behavioural patterns and population dynamics of the species’.
This study describes the behavioural ecology of the rock-wallaby subspecies P. l. lateralis in the central wheatbelt region of Western Australia. It focuses on environmental variables that have rarely been studied simultaneously, those of climate, fear of predation and conspecifics, and habitat structure. The Nangeen Hill Reserve population was chosen because it is one of seven small fragmented reserves, within a landscape, with strong seasonal climatic patterns. A methodological approach was developed that enabled identification of the key ecological determinants of the foraging and feeding behaviours of P. l. lateralis in this highly variable environment. The study included a comprehensive examination of all the behavioural characteristics and v abilities of P. l. lateralis, compiling a detailed behavioural repertoire (ethogram), a first for this species, and included both nocturnal and diurnal observations.
P. l. lateralis uses a complex arrangement of non-agonistic and agonistic behavioural acts that determines its social organisation, and indicates a linear dominance hierarchy. There is little vocal communication, and instead the rock-wallabies appear to rely on both ritualised behaviour acts and chemical cues to exchange information about the physiological or behavioural state of the individual, thus evolving very diverse and complex social behaviours. Nangeen Hill rock-wallabies occupy a permanent central rock refuge, with strong signs of site fidelity. Their foraging patterns reflect those of a central place forager, but distances travelled are restricted in open habitats, with stronger preferences for areas of rock structural complexity. Their foraging behaviour is not strictly nocturnal nor can it be considered crepuscular, exhibiting significantly different seasonal patterns. Time allocation for foraging is strongly affected by fear of predators and to a lesser extent conspecifics, and certain climatic conditions.
Although rock-wallabies use multiple behavioural strategies to reduce predation risk, energy costs, and intraspecific agonistic interactions, they can only can survive in their present environment if they have access to complex rock refuge. This rock resource not only enables them to avoid extreme ambient temperatures, but also gives them protection against predators particularly when environmental conditions are unfavourable. In addition, their cave refuge also gives them protection from precipitation, reducing heat loss, and provides a safe environment for both rearing young and for courtship without the cost of predation. Rock refuge is the most important resource that defines this species and is central to all aspects of its life history.
Although this reserve has been under a fox-baiting program since 1982, and subsequently resulted in a rock-wallaby population increase and habitat expansion, within the rocky outcrop (Kinnear et al., 1998), it was clear from my research that the ecological situation was more complex. There is a strong predation influence on the behaviour indicating that the population is now predominantly fear-driven. It is the fear of predators and dominant conspecifics that restricts both the foraging range and time spent feeding. This results in animals being tightly restricted to their rock refuge, resulting in overgrazing and habitat degradation. These concerns led me to believe that if the current situation was not alleviated, then a population crash was imminent. A population crash subsequently happened in 2010, and the cause of this decline is a result of a complex ecological relationship, that includes direct and indirect predatory effects, weed invasion, and drought. The results of this research and the subsequent recent population decline, show the importance of including behaviour into an ecological study to have a better understanding. It provides a better understanding of a species as well as providing important insights into its evolutionary past, and how this has shaped their social and demographic patterns. This research also demonstrates how the use of a permanent central rock refuge both contributes to the animal’s continued survival, and restricts its future distribution, particularly in ecologically altered landscapes.
Although this study was not designed primarily to resolve conservation and management problems, its findings are already being used to design an active management plan for the central wheatbelt rock-wallaby populations. The complex relationships between how an animal obtains and uses its resources, the availability of different vegetation patches, and population demographics creates significant problems for the management of a species. This emphasises the need for future research on all animal groups, to understand the relationships between the habitat and landscape elements, and that of behaviour and population dynamics. Understanding how animals perceive their environment and how they adjust to its changes will be paramount for the future management and survival of many species.