Left syringeal dominance in testosterone-treated female canaries.

Male canaries (Serinus canaria) produce most of their song syllable types on the left side of the syrinx, the two-sided vocal organ. Female canaries treated with testosterone propionate begin to sing in a male fashion, a behavior seldom seen in untreated females. To learn whether syringeal dominance occurs in testosterone-treated female canaries, we deactivated either the right or the left side of the syrinx by severing the tracheosyringeal nerve on that side. Recordings of the birds' songs were made before and after the nerve cut, and song analysis was based upon visual comparisons of sound spectrograms. Pre- and post-operative syllable types were identified by their frequency structures and repetition rates. Six of eight birds displayed clear left dominance as assessed by nerve cuts; therefore, we concluded that most, but not all, female canaries generate the majority of their syllable types with the left syrinx.