SUMMARYKnight, T. A. 1974. A review of hearing and song in birds with comments on the significance of song in display. Emu 74: 5–8.The songs of birds are produced by the modulation of air streams in the syrinx of the singing bird. The notes produced may be modulated in amplitude or frequency and serve to carry information. Noises occurring in display may also be produced by other means. The use of a given sound-structure depends upon the physical characteristics of the habitat in which it is commonly used.The differences in response between the human and avian ear may result in our own perception of the displays differing from that received by the birds. The relations of song to behaviour are complex.