Effect of syringeal denervation in the budgerigar (Melopsittacus undulatus): the role of the syrinx in call production.

In the budgerigar, the left and right tracheosyringeal nerves (ts) were sectioned both above and below the common anastomosis in order to assess the roles of the hypoglossal nuclei and syringeal muscle halves in the control of call production. Signal processing software was used to quantify changes in contact call fundamental frequency and duration, and similarity analysis for pre- and postsurgical contact calls was performed by means of spectrogram cross-correlation. After resecting a portion of either the right or left ts nerve above the anastomosis (thereby eliminating the input from the ipsilateral half of the brainstem), contact call fundamental frequency decreased 40-50% on Day 1 postsurgery, while call structure and duration remained largely unaffected. Fundamental frequency returned to normal within 4-7 days after surgery. In contrast, nerve sectioning below the anastomosis on either side of the syrinx (thereby eliminating input to the ipsilateral half of the syringeal muscles) resulted in moderately noisy harsh-sounding calls with little change in temporal characteristics. Thus, budgerigars differ from many oscines studied to date in that they do not demonstrate laterality in vocal control at the level of the syrinx. Vocalizations produced by birds after bilateral syringeal denervation were abnormal, consisting entirely of broadband harmonic sounds with very low fundamental frequencies (i.e., less than 900 Hz) and poor frequency modulation. In contrast, individual call durations, as well as the rhythm and patterning of vocalizations resembling warble song, were remarkably similar to presurgical recordings after both unilateral and bilateral ts nerve resection.(ABSTRACT TRUNCATED AT 250 WORDS)