SUMMARYMaclean, G. L. 1976. Rainfall and avian breeding seasons in north-western New South Wales in spring and summer 1974–75. Emu 76: 139–140.As a result of unusually heavy rains since 1973, many bird species in north-western New South Wales became seasonal breeders, starting to nest in the spring of 1974. Opportunistic breeding was no longer released by rainfall, probably because of some physiological or ecological feedback mechanism or both resulting from prolonged breeding since the start of the wet period (e.g. gonadal exhaustion, high population densities). This reflects an ancestral capacity in arid-zone birds to respond to environmental cues of a purely seasonal nature (photoperiod, temperature) rather than to the usual arid-zone cues of rainfall and the resulting improvements in food supply and vegetation.