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John Gould wrote many warnings about the potential extinction of Australian species. Ironically his collectors were killing thousands of birds and mammals all over the world to send to him for identification and illustration.
'It may be possible - and, indeed it is most likely - that flocks of Parakeets no longer fly over the houses and chase each other in the streets of Hobart Town and Adelaide, that no longer does the noble Bustard stalk over the flats of the Upper Hunter, nor the Emus feed and breed on the Liverpool plains, as they did at that time; and if this be so, surely the Australians should at once bestir themselves to render protection to these and many other native birds: otherwise very many of them, like the fine Parrot (Nestor productus) of Norfolk Island, will soon become extinct.'
Handbook to The Birds of Australia, 1865. Preface, p.xxiv.
Since the European colonisation of Australia, 21 species of mammals and 23 species of birds have become extinct.