THE PROCESS OF SYLLABLE ACQUISITION IN ADULT INDIGO BUNTINGS (PASSERINA-CYANEA)

Vocal learning in adult indigo buntings was studied by monitoring soci ally paired males housed together in sound isolation boxes. Two of thr ee yearlings socially paired with older birds in early spring acquired new syllables and reorganized their stereotyped and plastic songs, wh ile eleven yearlings socially paired later in the year largely Failed to acquire new material, as did the older adults socially paired at va rious times of year. Yearlings changed their stereotyped songs to more closely match their tutors' by replacing syllables or by inserting ne w syllables. This song matching involved two processes in which adult plastic song played a role: (1) new syllables were developed in plasti c song, and (2) newly mastered or pre-existing syllables were transfer red from plastic song into stereotyped song. Morphological similarity between yearlings' and tutors' syllables strongly influenced which syl lables yearlings retained. After social pairing, matching syllables te nded to be delivered more frequently by yearlings and become incorpora ted into their stereotyped songs, while non-matching syllables tended to decline in use or be discarded altogether. New syllables were forme d from existing syllables most morphologically similar to the ''target '' syllable, through transformation and combination of existing syllab les. As new forms became more common, old forms declined and eventuall y were discarded. Our data suggest that adult indigo buntings maintain the ability to sing stereotyped songs while new material is mastered, and held in reserve, in plastic song. Acquisition of new syllables in yearling indigo buntings requires trial-and-error learning, but proce eds without overproduction and subsequent attrition of distinct syllab le types, and does not substantially rely on improvisation and inventi on. Rather, syllable acquisition and changes to stereotyped songs are strongly influenced by the pre-existing syllable repertoire.