Nervous control of the syrinx in White‐throated sparrows ( Zonotrichia albicollis )

This study reports the results of sectioning of the motor nerves to the syrinx and tongue in 31 North American White‐throated sparrows, Zonotrichia albicollis . Unilateral sectioning of the hypoglosso‐cervicalis and its branch the cervicalis descendens superior to the syrinx produce maximum qualitative distortions when performed on the left side and none, or hardly any, when performed on the right side. The effective operations eliminated the pure whistles of the songs which were then replaced by shrill patterns with a lower relatively constant fundamental frequency accompanied by two or more strong harmonics. Two individuals sectioned through the left hypoglosso‐cervicalis were somewhat exceptional in that one continued to sing the first half of the song normally while the second half deteriorated. The second individual eventually lost its song entirely except for audible clicks apparently where the whistles would otherwise have ended. Unilateral sectioning of the cervicalis ascendens to the tongue as well as sham operations had no noticeable qualitative effects. Bilateral sectioning of the cervicalis descendens superior gave results similar to sectioning on the left side. In addition such birds produced whistles and rasping sounds in association with breathing. Some quantitative differences were noted in whistles and intervals between whistles. The occurrence of these changes were not consistent within a group and occurred widely in most groups without regard to the side operated upon. The results confirm that output of sound from the syrinx in most individuals is primarily from the left side. Membranes on the affected side continue to vibrate under the pressure of air expelled from the lungs, but with strong harmonics and at frequencies determined only by the properties of the membranes and syrinx and in relation to the force of the expelled air. Summary Sectioning of motor nerves to the syrinx of North American White‐throated sparrows confirms the lateral output of song primarily by the left side of the syrinx. One individual showed evidence of singing from both sides. There is also evidence that sectioning of motor nerves may have quantitative effects on the durations of whistles and intervals between whistles, particularly at the beginnings of songs. This suggests that singing is controlled dynamically through the interaction of central and peripheral controls.