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The six species of marsupials in the genus Dasyurus are known as quolls. Four species are found in Australia and two (D. spartacus and D. albopunctatus) in New Guinea. Habitats include dense, moist forests (D. maculatus); drier forest and open country (D. viverrinus); savannah (D. geoffroii); woodland and rocky areas (D. hallucatus); low savannah (D. spartacus); and a range of conditions up to 3500 m for D. albopunctatus. All species are mainly nocturnal and mainly terrestrial, although they are good climbers. They are all predators, although some plant material may also be eaten. The diet of the smaller species is largely insects, but D. maculatus may take mammals as large as wallabies. (Nowak 1991)
Several quoll species have experienced severe population declines since European settlement of Australia. For example, the Western Quoll or Chuditch (D. geoffroii) was once distributed over nearly 70% of the Australian mainland but is now found on less than 2% of the continent. Factors believed to have driven this decline include land clearing, degradation of habitat by introduced herbivores, persecution by humans, altered fire regimes, epidemic disease, and the impacts of introduced foxes (Vulpes vulpes) and feral cats (Felis catus). Foxes and cats may compete with Western Quolls for limited food resources and, perhaps more importantly, may kill quolls in direct encounters (cats and especially foxes may be three to four times the size of a Wester Quoll, which can grow to around 2 kg). (Glen et al. 2009 and references therein)
The Northern Quoll (D. hallucatus) has been seriously threatened by the invasion of the highly toxic cane toad (Bufo marinus). Following toad invasion, local quoll populations have disappeared across Northern Australia. Cane Toads were introduced to Queensland in 1935 and have since spread across northern Australia. Because this toad's toxins are very different from those found in native frogs, many native vertebrate predators die after attacking or consuming toads. In northern Australia, Cane Toads have caused severe population declines of varanid lizards and freshwater crocodiles as well as Northern Quolls.
A range of conservation efforts have been pursued to blunt the impact of the toads, including the translocation of Northern Quolls to islands that remain free of Cane Toads. O'Donnell et al. (2010) reported on another strategy, namely training Northern Quolls to associate toads with nausea without actually exposing them to the toad toxins. Initial trials were promising, with "toad-smart" quolls less likely to attack toads and exhibiting increased short-term survival rates in the wild (interestingly, females, independent of their training, were also less likely to attack toads). The authors observations also confirmed claims by others that consuming toads poses a serious threat to Northern Quolls. They report that they observed four "toad-naıve" quolls within hours of their release attacking large toads, then convulsing and dying.