Figure 1. Modulation of the respiratory rhythm in two different songbirds species.

Amplitude and temporal pattern of respiratory pressure (P, horizontal line indicates ambient pressure) during vocalization (illustrated as spectrogram in top panel) change markedly from that during normal, silent respiration. Top: Zebra finch song consists of a repetition of a motif (M) composed of 4 (in this example) distinct pressure pulses (top), which is repeated four times in the depicted song bout. A distance call (C) precedes the song bout. Bottom: Canary song is generated with a series of pressure pulses that give rise to different trills. Each sound of the various trills corresponds to an air sac pressure peak, either during a sustained expiratory pressure pulse (first pulse of song) or during rapid alterations between expiration and inspiration (mini-breaths). Song is a series of different trill patterns, each generated by a series of stereotyped respiratory pulses. The respiratory pattern of song therefore contains a sequence of different respiratory rhythms.