Spectrograms show that sounds in the rainforest have evolved to occupy different frequency bands almost like the different frequencies of broadcast radio waves. There is a surprising degree of separation both in the frequency and time domain, which, it could be speculated, is to avoid interference with each other’s ‘broadcast range’ (fig. 10.7) . Indeed, research has shown that birds may vary the pitch of their song in order to avoid them being masked by insect noise (Kirschel et al., 2009).


Figure 10.7 The top spectrogram shows a typical rainforest at dawn with different sounds exhibiting a large degree of separation as if occupying the different frequency bands of a radio.