A syringeal muscle encodes both the timing and frequency of birdsong

Understanding how motor commands are transformed into vocal behavior requires linking neural activity, physiology, and the nonlinear dynamics of the vocal organ. In birdsong, a widely used framework assigns distinct functional roles to syringeal muscles, separating the control of phonation timing from the modulation of acoustic structure. Here, we build on this view by analyzing simultaneous recordings of syringeal electromyographic activity and respiratory pressure in singing canaries ( Serinus canaria ). We find that the syringealis ventralis muscle (vS), beyond its established role in frequency control, encodes information about phonation timing: periods of suppressed oscillations under otherwise permissive pressure conditions are consistently associated with transient increases in vS activity. Within a low-dimensional dynamical model of the syrinx, this dual role arises naturally from the nonlinear interaction between motor commands and the biomechanics, suggesting that timing and spectral features can be jointly encoded through concurrent motor actions. As a consequence, vS activity alone contains sufficient information to reconstruct both the temporal and spectral structure of song, enabling realistic synthesis from a single physiological variable. This reduction provides a new perspective on motor replay during sleep, where much syringeal activity occurs in the absence of song-like respiratory patterns, and suggests a route to infer and synthesize the acoustic structure of internal motor sequences.