SUMMARYAbbott, I. 1974. The avifauna of Kangaroo Island and causes of its impoverishment. Emu 74: 124–134.Kangaroo Island has 50 per cent of the species of landbirds that breed on Fleurieu Peninsula, 14 km distant, and about 80 per cent of the species on Yorke or Eyre Peninsulas. Though often visited by ornithologists during the last 67 years. 55 species of landbirds known on the mainland have never been recorded. 33 others have teen recorded less than five times. The marked avifaunal impoverishment of the island is probably not because of differences in habitat OT vegetation, but because these 88 Species have immigrated very seldom to the island.The pattern of distribution of 226 species of landbirds over southern Australia, including Tasmania and the islands in Bass Strait, suggests that nearly 25 per cent of these arrived postglacially in coastal South Australia. Probably only 25 of the 90 species absent from Kangaroo Island were there in the past but have became extinct. Sixteen of these occur in Tasmania but not on any Bass Strait islands, and are presumably extinct there also. One native species has established itself on Kangaroo Island in the last 67 years.The theoretical expectation that island populations should have more variable bills or tarsi than mainland populations was confirmed respectively for maleAcanthiza pusillaand femalePhylidonyris pyrrhoptera.