Unilateral nervous control of the syrinx in java sparrows (Padda oryzivora)

Abstract

The syrinx of song birds contains two sound sources, the internal tympaniform membranes located one in each bronchus, that are controlled by the syringeal musculature. These muscles are innervated by the cervicalis descendens superior (CDS) branch of the hypoglossal nerve. Unilateral sections of the left CDS nerve in Java sparrows markedly disrupted tonal quality of the songs, although temporal parameters were unaltered. Bilateral CDS nerve sections caused greater disruption in frequency characteristics and temporal parameters were altered. Most birds died due to asphyxia soon after the operation. Right CDS nerve sections had much less effect, except on long whistles where extra low frequency sounds appeared, probably from the denervated right bronchus. Intact song pattern was restored within four months without re-innervation of the right syringeal musculature. This unilateral dominance in the control of the syrinx agrees with previous work and adds to the support for the “two voice” theory of sound production in birds (Greenewalt, 1968; Stein, 1968).