song control may be lateralized, motor control of respiratory muscles possibly remains bilateral. Muscles of the syrinx are controlled by the tracheosyringeal branch of the hypoglossal nerve. Each syringeal half is ipsilaterally innervated by the hypoglossal motor nucleus (XIIts) in the brain, which in turn receives projections—mainly ipsilateral—from nucleus robustus (RA), an important song control nucleus that also regulates respiratory muscles. Laterality of song control has been observed all the way into the higher vocal center (HVC) brain region; unilateral lesions to HVC produce lateralized effects in the temporal patterning of song in the zebra finch. See also Bird song: Neuroanatomy Species-specific examples Canary (Serinus canaria) The waterschlager canary is the most robust example of unilateral syringeal dominance, creating song of which 90% of the syllables are produced by the left syrinx, as determined by recording respiratory pressure and airflow through each side during singing. Waterschlager canaries with left tracheosyringeal nerve cuts are only able to produce up to 26% of the pre-operation syllable repertoire. The waterschlager canary strain is conspecific to the domestic canary but has been inbred by humans for its beautiful song. The outbred domestic canary, however, does not exhibit the strong lateralization of the waterschlager canary. Possibly explaining their strong left lateralization, canaries of the waterschlager strain contain an inherited auditory defect that decreases their sensitivity by up to 40 dB to sounds higher than 2 kHz, which are produced mainly by the right side of the syrinx. Brown-headed cowbird (Molothrus ater) The brown-headed cowbird produces very rapid clusters of notes that alternate in frequency, with the right syrinx producing the high frequency notes and the left syrinx producing low frequency notes. The entire cluster is sung during a single respiratory expiration, called "pulsatile expiration", in which no inflow of air occurs between notes. By alternating note production successively between each side of the syrinx and without ceasing expiration, a cowbird is able to rapidly and abruptly switch the frequency of notes back and forth between high and low frequencies. To see a cartoon of how syllables are produced in alternate sides of the syrinx, click here Northern cardinal (Cardinalis cardinalis) Northern cardinals contain FM sweep syllables as part of their repertoire that begin around 6 or 7 kHz and sweep downward continuously to 2 kHz. Each of these syllables is sung unilaterally. However, the cardinal switches mid-syllable from employing the right syrinx at the high