frequency beginning of the sweep to the left syrinx at the lower frequency end. This switch usually occurs when the sweep reaches the 3.5 to 4.0 kHz range. The transition is abrupt yet timed so precisely that neither sonograms nor audition can detect the switch. To see a cartoon of how the syrinx produces cardinal song, click here. Northern mockingbird (Mimus polyglottus) Because the mockingbird has the ability to mimic the songs of other species, it has been useful in determining whether the vocal motor patterns employed by particular species in producing their unique song types are constrained by acoustic properties or whether the unique song types may also be produced by different motor patterns generated by the same songbird vocal system. When juvenile mockingbirds were tutored with the recorded or synthesized song of a cardinal or cowbird, the mockingbirds employed the same respiratory and lateralized vocal pattern as the original species to produce its mimicked song. When the mockingbird motor pattern differed from the tutor motor pattern, the song output also differed, suggesting that the vocal motor pattern is largely determined by the acoustic restraints of the song type. Even though the mockingbird was able to mimic the FM sweeps of cardinals by employing the same motor pattern—switching mid-syllable from right syrinx to left syrinx—the mockingbird did not perform the transition seamlessly. This indicates that precise unilateral control of song production in the syrinx of certain birds, such as cardinals, has allowed them to become unique vocal specialists. Possible functions Because the lateralized control of songs of certain species, such as cardinals, demands such precision in motor control, the ability to produce high-quality, seamless syllables may provide an indicator of fitness to potential mates. Supporting this hypothesis, certain syllables called "sexy syllables" sung by male canaries at high frequency are more effective than others in eliciting sexual displays from females. These particular syllables all contain two notes that are sung alternately by each side of the syrinx. Thus, control of the rapid switching from one side of the syrinx to the other is required to produce these attractive syllables. Lateralization also allows for rapid and abrupt frequency changes. Studies of mockingbirds mimicking tone pairs in which the first tone was either higher or lower than a median tone of 2 kHz (either side is capable of producing this median tone) revealed that alternating sides of the syrinx for each