Ecology and predator associations of the northern quoll (Dasyurus hallucatus) in the Pilbara

Abstract

The northern quoll (Dasyurus hallucatus) is an endangered carnivorous marsupial in the family Dasyuridae that occurs in the northern third of Australia. It has declined throughout its range, especially in open, lowland habitats. This led to the hypothesis that rocky outcrops where it persists provide a safe haven from introduced predators and provide greater microhabitat heterogeneity associated with higher prey availability. Proposed causes of decline include introduced cane toads (Rhinella marina, which are toxic), predation by feral cats (Felis catus), foxes (Vulpes vulpes), and the dingo (Canis lupus), and habitat alteration by changes in fire regimes. The National Recovery Plan highlighted knowledge gaps relevant to the conservation of the northern quoll. These include assembling data on ecology and population status, determining factors in survival, especially introduced predators, selecting areas that can be used as refuges, and identifying and securing key populations. The Pilbara region in Western Australia is a key population currently free of invasive cane toads (a major threat).The Pilbara is a semi-arid to arid area subject to cyclones between December and March. I selected two sites: Millstream Chichester National Park (2 381 km2) and Indee Station (1 623 km2). These are dominated by spinifex (hummock) grasslands, with rugged rock outcrops, shrublands, riparian areas, and some soft (tussock) grasslands. They are subject to frequent seasonal fires, creating a mosaic of recently burnt and longer unburnt areas. The overall aim of this study was to assess the ecology of the northern quoll in the Pilbara to understand drivers of density and distribution of this endangered species, to enhance species-specific conservation efforts. I collected field data on six one-month trips over three years, predominantly using live-trapping, camera-trapping, sampling invertebrates, vegetation surveys, habitat structure, and den availability surveys.In the Pilbara, the largest mammalian predators are the introduced dingo and feral cat. The largest native mammalian carnivore is the northern quoll, which is smaller than the introduced predators but larger than the other dasyurids in the guild. In Chapter 2, I explored spatial and temporal associations among introduced predators and quolls and their associations with habitat to assess the impact of introduced predators on quolls. I found evidence that dingo control programs prevent dingoes from fulfilling their role as top predators, leading to mesopredator release of feral cats. Feral cats were associated with open habitats (spinifex grasslands and recently burnt areas), and showed inverse associations to those of quolls, suggesting that quolls avoid cats in space. Quolls were positively associated with rocky habitats. In Chapter 3, I assessed spatial and temporal associations among dasyurids to understand the current role of northern quolls within their guild. I found that range contraction of northern quolls into rocky habitats prevent them from fulfilling their role as top predators across the landscape, potentially leading to mesopredator release of kalutas (Dasykaluta rosamondae). Kalutas were associated with spinifex grasslands and may be controlling densities of smaller dasyurids such as stripefaced dunnarts (Sminthopsis macroura), which more often inhabit recently burnt areas.Northern quolls have a synchronized annual reproductive cycle in which births are timed to enhance offspring survival by coinciding with seasonal resources. The northern quoll now occurs in patchy populations. The Pilbara is the most arid and southern portion of its range In Chapter 4, I analysed demography and population dynamics to determine differences and similarities of this range extreme with other populations across their range. I found that the reproductive timing of northern quolls in the Pilbara differs from that of populations in more mesic and lower latitude regions where they have been studied previously. This is consistent with the hypothesis that dasyurids respond to differences in food availability, so they time reproduction to coincide with peak resources.I assessed different aspects that contribute to defining habitat quality for northern quolls to understand if and how bottom-up processes regulate their apparent preference for rocky habitats (Chapter 5). For this I looked at den availability, vegetation cover and diversity, and availability and diversity of potential vertebrate and invertebrate prey. Except for a few dens in riparian areas, rocky habitats were the only areas with dens available at my sites. Rocky habitats had consistently more shelter, despite better vegetation cover at the ground level provided by spinifex grasslands and shrublands. Prey availability was strongly seasonal. Spinifex grasslands had the highest records and diversity of both vertebrates and invertebrates, and rocky habitats also contained high abundance of vertebrates when corrected for sampling effort. Soft grasslands contained few potential prey. I found that quolls ate more vegetation during the pre-mating season (June), ate more animal prey when females carry pouch young and had high energy demands (September), and a higher percentage of invertebrates during the recruitment season (April).