In this study, the unilateral and bilateral syrinx nerve (NXIIts) were resected in the red-billed Leiothrix ( Leiothrix lutea
) to assess the roles of NXIIts in vocalization. Wavesurfer and Sound Analysis Pro were used to analyze pre- and postsurgical acoustic changes. After resecting of unilateral NXIIts, red-billed Leiothrix produced the common calls with lengthened syllable interval, shortened duration and a declined FM index. The effects of left NXIIts resction on temporal and spectral characteristics of syllables were more significant than that of right NXIIts. These results indicated that the neural control of NXIIts was unilateral and left-side dominated. Moreover, the left NXIIts could produce high frequency components and harmonic waves. After resecting of bilateral NXIIts, the calls were characterized by monotone, reduced loudness and increased syllable pulse numbers.