Causes of the extinction of native mammals of the Western Division of New South Wales: An ecological interpretation of the nineteenth century historical record

Twenty-four mammal species - predominantly the medium-sized. ground-dwellin g mammals with a dependence on grass/herbs and seeds - disappeared forever from the landscape of the Western Division of New South Wales in a period o f 60 years from first settlement in 1841. The present study examines the ca uses of this extinction episode by constructing a picture of the changing l andscape from the historical record and interpreting the findings ecologica lly. The conclusions point to an extinction process that can be largely att ributed to the impact of sheep, an impact that was exacerbated in the scarc e and fragile refuges of the fiat landscape in times of intense and frequen t drought. This conclusion differs from those of many others, particularly Kerin in the Western lands Review. who pointed to ''the impact of feral ani mals, rather than overgrazing" as the cause of mammal extinctions- and Mort on, who considered that the rabbit was "principaily (although not entirely) " responsible for mammal extinctions in the rangelands. The rabbit plague i n the Western Division from the early 1880s and the influx of foxes in the last years of the 19th century expedited the local demise of some species a nd even delivered the final blow to surviving remnant populations of a few species of native mammals, but they were nor the primary agent of extinctio n. Historical accounts give prominence to the rapidly growing wool industry in the 19(th) century. From its dominant position as an export commodity, wool became the chief means of the successful spread of colonial settlement . By 1853 there were about 300.000 sheep based at the southern end of the D arling on the watered frontages, which were all taken up by 1858. The west of the Darling was largely occupied by sheep farmers between 1859 and 1876. The history of settlement around Menindee from 1841 can be read as a devas tating critique of the failure to realist: that the west could not sustain a pattern of land use imposed on it from another world. The deterioration o f the pastoral landscape was such that by the late 1880s the "walls of the pastoral fortresses... were beginning to crumble of their own accord as the foundations on which they were built - the physical environment - altered under stresses...". The sequence of occupation and land use in the Western Division and the timing of the loss of native mammal species allows the con clusion to be drawn that it was sheep, and the wall the land was managed fo r the export wool industry that drove so many of the mammal species to exti nction. The impact of ever increasing millions of sheep on all frontages, t hrough all the refuges, and across ail the landscape by the mid 1880s, is t he primary cause of the greatest period of mammal extinction in Australia i n modem times.