Animated Films of Song Production in Songbirds
The following QuickTime movies illustrate the different way in which Northern
Cardinals (Cardinalis cardinalis) and Brown-headed Cowbirds (Molothrus ater
ater) use their bipartite syrinx to produce their distinctive species-specific
songs.
You may obtain permission to download these movies for non-commercial use in
instructional settings such as classrooms or lectures at no cost, by sending an
email request to Rod Suthers suthers(at)indiana.edu.
The accompanying wav files are in stereo so right and left side of the syrinx
are heard on the corresponding speakers.
View Northern Cardinal Vocal Production Movie:
Click on either of links below picture to play video.
Play as WMV file Play as SWF file
The songs of Northern Cardinals often include frequency modulated notes or syllables that sweep through a wide range of frequencies. Cardinals sing fundamental frequencies below about 3.5 kHz with the left side of their syrinx and higher frequencies with the right side. Continuous broad-band frequency sweeps are produced by switching sound production from one side to the other midway through the note. Most birds make this switch with such precise coordination that it is not detectable in the emitted vocalization. In this example, phonation switches from the right to left side of the syrinx during the downsweep. Upward sweeping notes are produced beginning on the left side and switching to the right.
View Brown-Headed Cowbird Vocal Production Movie:
Click on either of links below picture to play video.
Play as WMV file
Play as SWF file
The Brown-headed Cowbird uses a different pattern of syringeal lateralization.
Cowbird songs contain 2 or 3 note clusters, each produced during a single
breath. These are followed by a loud high pitched final whistle. Successive
notes in each note cluster are produced on opposite sides of the syrinx,
beginning with the left side for the first note. By alternating sides in this
way the cowbird can adjust the silent side of the syrinx to start its note at a
different pitch without a frequency slur between notes that follow each other
without a silent interval between them. The final whistle is always sung on the
right side.
The vocal organ or syrinx of Oscine songbirds is located at the junction
between the primary bronchi and the trachea. Sound is generated by air flowing
across a pair of fleshy tissue pads, the labia, present at the cranial end of
each bronchus. The songbird syrinx thus contains two separate sound sources,
one in each bronchus. Sound production in each bronchus is controlled
independently by several muscles that are innervated by motor neurons in the
tracheosyringeal branch of the hypoglossal nerve coming from the same side of
the brain. During song, the labia on the side or sides of the syrinx that are
producing sound are moved toward each other into the airflow through the
bronchus, which is thought to generate Bernoulli forces causing them to vibrate
and produce sound.
This bipartite syrinx with its two independent sound sources increases the
diversity and acoustic complexity of bird song. Different species achieve
different vocal effects by using the two sides of their syrinx in different
ways. Some birds, such as grey catbirds and brown thrashers, can simultaneously
produce different sounds on each side of the syrinx that are not harmonically
related to each other. It is also possible to produce sound on only one side or
to switch sound production from side to side by fully adducting the labia until
they meet and close the bronchial lumen. This stops air from flowing through
that side of the syrinx and silences it. Vocal diversity is increased by the
fact that each side of the syrinx tends to be specialized in certain ways. The
right side of the syrinx, for example, generally can produce a higher range of
frequencies than can the left side.