Birds breathe and sing at resonances of the biomechanics

Evolution has shaped animal bodies, yet to what extent biomechanical devices provide constraints and opportunities across different behaviors remains unclear. In birds, quiet breathing operates at a resonance of the respiratory biomechanics, but song, a behavior thought to be shaped by strong sexual selection, requires much higher breathing rates. Combining physiological recordings with a nonlinear biomechanical model, we show in canaries (Serinus canaria) that song production drives the system into a nonlinear regime that broadens the frequency range of amplified responses. This enhancement encompasses all syllabic rates, with an average magnification of ~94% of the theoretical maximum. Our results show that birds breathe and sing at a resonance, revealing that optimization strategies can be shared across behavioral states and extend to sexually selected displays.