In 1912, the Australian ornithologist Gregory M. Mathews recognised three living subspecies of emu, "D. n. novaehollandiae" (Latham, 1790), "D. n. woodwardi" Mathews, 1912 and "D. n. rothschildi" Mathews, 1912. The Handbook of the Birds of the World, however, argues that the last two of these subspecies are invalid; natural variations in plumage colour and the nomadic nature of the species make it likely that there is a single race in mainland Australia. Examination of the DNA of the King Island emu shows this bird to be closely related to the mainland emu and hence best treated as a subspecies.