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Patterns in the modern decline of western Australia's vertebrate fauna: Causes and conservation implications

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The conservation status of terrestrial vertebrates occurring on the mainland of Western Australia was assessed. Extinctions and declines are virtually confined to non-flying mammals with mean adult body weights between 35 g and 4200 g. Variation in patterns of attrition within this critical weight range (CWR) can be explained almost entirely by a combination of regional patterns in rainfall and, to a lesser extent, species' habitat and dietary preferences. Similar patterns of mammal attrition were recognisable throughout the continent, except that the CWR was 35 to 5500 g.Environmental changes since European settlement have emulated an increase in aridity by reducing the environmental productivity available to vertebrates. These include the diversion of environmental resources to humans and introduced species, and a reduction in vegetative cover by exotic herbivores and changed fire regimes. Our analyses support the view that the reduction in available productivity has caused CWR mammals to suffer the greatest attrition because of their limited mobility, but relatively high daily metabolic requirements. The direct elimination of confined populations of mammals by exotic predators has exacerbated this attrition. We derive priorities for the conservation of Australian mammals.
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... One of the primary threatening processes driving global species decline and extinction is invasive predators, with the feral cat (Felis catus) and the red fox (Vulpes vulpes) having particularly devastating effects on native wildlife populations (Bellard et al., 2016;Doherty et al., 2016;IUCN, 2022;Kearney et al., 2019). In Australia, species at the highest risk of predation by feral cats and foxes are mammals that fall within the Critical Weight Range (CWR), between 35 and 5500 g (Burbidge & McKenzie, 1989). ...
... However, few studies have looked at the response of smaller species, such as small mammals and reptiles and the impact that predator control has on these in situ species. Small mammals and reptiles are the preferred prey of feral cats and are therefore likely to show a strong response to predator control (Burbidge & McKenzie, 1989;Kutt, 2012;Read et al., 2022). In particular, native rodents have been shown to increase in abundance after the removal of feral cats and foxes (Moseby et al., 2009;Risbey et al., 2000;Tuft et al., 2021). ...
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Context. The decline of the greater bilby (Macrotis lagotis), or Ngarlgumirdi (Yawuru), like other critical-weight range Australian mammals, is believed to be primarily due to the synergetic impacts of predation by feral cats and foxes, habitat disturbance caused by large introduced herbivores, and increases in the frequency and intensity of wildfires. Although it has been demonstrated that low-intensity prescribed burning mosaics in some habitats have the potential to benefit mammals, including Ngarlgumirdi, by creating habitat with sufficient vegetation cover, the contributions of specific fire-mosaic attributes to Ngarlgumirdi persistence remain unclear. Aims. To elucidate the impacts of fire-mosaic attributes on the occupancy of Ngarlgumirdi on the Dampier Peninsula. Methods. We used 2-ha sign-plot data collected by four Indigenous Ranger groups, in combination with 20 years of satellite-derived fire-history information to investigate the multiscale impacts of fire attributes on Ngarlgumirdi and feral cats (Felis catus) on the Dampier Peninsula in the West Kimberley region, a large, unfenced landscape in the most fire-prone section of the Ngarlgumirdi's current range. Key results. We found that Ngarlgumirdi was more common in areas that had a higher proportion of habitat that had not burnt for at least 3 years, whereas feral cats were less prevalent in these areas. Similarly, Ngarlgumirdi was less likely to occur in landscapes affected by frequent fires, whereas cats were more common there. Conclusions. Our findings have highlighted the importance of decreasing fire frequency and increasing the extent of long-unburnt habitats (>3 years) for preserving Ngarlgumirdi on the Dampier Peninsula and mitigating ecological damage inflicted by feral cats. Findings were consistent across spatial scales (1-, 3-, 5-and 10-km radius from each monitoring site). Implications. These results have demonstrated the potential of fire management to increase native species resilience in the absence of direct feral cat control methods. Further, they support a recent cross-tenure initiative led by Traditional Owners to implement fire management that aims to reduce large, frequent high-severity wildfires and increase areas of long-unburnt vegetation on the Dampier Peninsula.
... However, dramatic declines have since been documented across the monsoon tropics (Woinarski et al. , 2011aZiembicki et al. 2013;Davies et al. 2018a;Campbell et al. 2022). As in other parts of Australia, declines in northern Australia have been concentrated in the 'critical weight range' (species with body weight of 35-5500 g (Burbidge and McKenzie 1989;Murphy and Davies 2014)) and in more open habitats and less rugged areas, especially in lower rainfall zones Stobo-Wilson et al. 2019;von Takach et al. 2020). Presently, only a few isolated regions in the monsoon tropics are known to support comparatively healthy mammal populations: the Tiwi-Cobourg bioregion (consisting of the Tiwi Islands and Cobourg Peninsula) in central northern Australia; parts of the North Kimberley bioregion in northwestern Australia; and some offshore islands in the Arnhem Coast bioregion, of which the largest is Groote Eylandt (Start et al. 2007;Murphy and Davies 2014;Heiniger et al. 2020). ...
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Context Native mammals continue to suffer widespread and severe declines across northern Australia’s tropical savannas. There is an increasing body of evidence that the primary driver of these declines is predation by feral cats (Felis catus) and that this is exacerbated by high-severity disturbance regimes (frequent high-intensity fires, and grazing and trampling by exotic megaherbivores) that simplify habitat, thereby increasing hunting efficiency. The large islands off the northern Australian coast – where some threats are either reduced or absent – provide a means of testing the conceptual model’s predictions. Aims To compare the trajectory and distribution of native mammal populations on two large, adjacent islands with markedly different disturbance regimes. Methods In 2020 and 2021, we resurveyed 111 historical sites across the two largest of the Tiwi Islands, Bathurst Island (42 sites) and Melville Island (69 sites) that were previously surveyed between 2000 and 2002. The Melville Island sites had also been resurveyed in 2015. We used the same live trapping method used in 2000–2002, supplemented with camera trapping. Key results On Bathurst Island, feral cats are rare, and we found no significant decrease in native mammal trap success or species richness, and the threatened brush-tailed rabbit-rat (Conilurus penicillatus melibius) appears stable. Conversely, cats occurred at relatively high abundance on Melville Island, and there was a 52% decline in trap success, a 47% reduction in species richness, and a 93% decline in trap success for the brush-tailed rabbit-rat over the 20-year period. The highest decreases in native mammal abundance and richness were in areas that were frequently burnt and had higher activity of feral cats. In contrast, in the absence of cats on Bathurst Island, native mammal abundance increased in frequently burnt areas. Conclusions While Bathurst Island remains one of Australia’s most important refuges for native mammals, neighbouring Melville Island is experiencing severe and ongoing mammal decline. We contend that this pattern primarily reflects the high abundance of cats on Melville Island compared to Bathurst Island. Implications Native mammal decline in northern Australian savannas is associated with abundant feral cats, but the relative contribution of disturbances in driving cat abundance remains less clear. An improved understanding of the constraints to feral cat populations in tropical savannas could enhance conservation management.
... biological factors (such as diet and shelter habitat). Burbidge and McKenzie (1989) coined the term 'critical weight range' for what others often term 'medium-sized' mammals, describing the range in body weight of those species that had suffered extinction or a significant geographic range decline. They defined the CWR as being non-flying mammals between 35 g and 5 500 g mean adult body weight, noting, as had some earlier authors, that the large wallabies and kangaroos and the ...
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A festchrift for Emeritus Professor Don Bradshaw, Chair of Zoology 1976-2004 Edited by Brention Knott and Jamie O'Shea (2009)
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This report provides an overview of the impact of feral cats Felis catus on native fauna of the Pacific region, with particular reference to Australia and its island territories. In Australia, cats take a wide variety of native species of mammals, birds and reptiles, but show evident preference for young rabbits or small marsupials where these are available. Reptiles are taken primarily in arid habitats, while birds often feature predominantly in the diet of cats on islands. Despite their catholic diet, population-level impacts of feral cats on native fauna have been poorly documented. There is considerable potential for competition to occur between cats and carnivorous species such as quolls and raptors, but no critical evidence has yet been adduced. There is also potential for amensal impacts to occur, either via transmission of the pseudophyllidean tapeworm Spirometra erinacei or of the protozoan parasite Toxoplasma gondii, but evidence for deleterious effects in free-living animals is not compelling. Direct predatory impacts have been inferred from anecdotal and historical evidence, more strongly from failed attempts to reintroduce native species to their former ranges, and most critically from the decimation of island faunas and responses of prey species following experimental removal of cats or reduction of cat numbers. Attributes of the biology of feral cats and their prey species derived from the literature review were used to develop a rank-scoring system to assess the susceptibility of native species to cat predation. Species listed federally as endangered or vulnerable were designated as being at zero, low or high risk of impact from cats according to their attribute scores, and their distributions mapped from primary sources and actual locality data. Based on the number of threatened species they contain, localities and regions within Australia were placed in order of priority for future research to clarify the precise impacts of feral cats. Although difficult and expensive to carry out, controlled and replicated field removal experiments are recommended to elucidate cat impacts in all mainland areas. Removal of cats should take place also on offshore islands and island territories, but only if pilot studies show that this will not release populations of alternative predator species such as introduced rats. If release appears likely, cats should be removed only as a component of an integrated control program that targets all relevant predators.
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At least 16 species of Australian mammals have become extinct over the past 200 years. Without islands, however, this figure would be even worse as nine species that were formerly widespread on mainland Australia were or are restricted to land-bridge islands. In addition, 13 species and subspecies of endangered and vulnerable mainland mammals that still occur on the mainland have island populations, reducing their chance of extinction. In all, 43 islands protect 29 taxa of Australian threatened mammals. Since European settlement some island mammal populations have become extinct, while many new populations, of both Australian and exotic mammals, have been established. The extinction of island native mammal populations is significantly correlated with the introduction of exotic mammals. Management of islands needs to concentrate on four areas: quarantine, monitoring (of both native mammals and possible introduction of exotics), eradication of exotics and translocations of native species. Prevention of introduction and establishment of further exotics to important islands through quarantine procedures is vital, especially for islands with permanent or temporary human habitation. Eradication or control of existing exotics is required for many islands and eradication of further introductions, as soon after detection as possible, should be a high priority action for nature conservation agencies. Past exotic mammal eradications and needs for the future are discussed. Translocations of island mammal populations to the mainland should take place only where the species is extinct on the mainland. Translocation to islands, where translocation to or on the mainland is not feasible, is an important conservation technique. Islands with exotics can be of value for re-introduction of locally extinct mammals or introductions (marooning) of threatened species that are at risk from feral predators on the mainland once the exotics have been eliminated.