Between the first Australian-wide aerial survey of kangaroos in 1980-82 and the second in 1984, indices of relative abundance determined by the same methods show that red kangaroos declined by 24% and western and eastern greys by 35%. The declines are attributed mainly to drought in the eastern half of the continent, partly offset by increases in the western half. We estimate numbers in 1984 at 6.3 million red kangaroos (cf. 8.3 in 1980-82), 1.2 million western greys (1.8) and 5.8 million eastern greys (9.0), a total of 13 millions of all three species compared with 19 millions in 1980-82. This is an overall drop of about 30%. Because recent work suggests that the sightability of both species of grey kangaroos is lower than that for reds, estimates of grey kangaroos will be less than the real numbers and should, therefore, be regarded as indices of relative abundance rather than as absolute estimates
