No abstract

Vocal learning in adult indigo buntings was studied by monitoring socially paired males housed together in sound isolation boxes. Two of three yearlings socially paired with older birds in early spring acquired new syllables and reorganized their stereotyped and plastic songs, while eleven yearlings socially paired later in the year largely failed to acquire new material, as did the older adults socially paired at various times of year. Yearlings changed their stereotyped songs to more closely match their tutors' by replacing syllables or by inserting new syllables. This song matching involved two processes in which adult plastic song played a role: (1) new syllables were developed in plastic song, and (2) newly mastered or pre-existing syllables were transferred from plastic song into stereotyped song. Morphological similarity between yearlings' and tutors' syllables strongly influenced which syllables yearlings retained. After social pairing, matching syllables tended to be delivered more frequently by yearlings and become incorporated into their stereotyped songs, while non-matching syllables tended to decline in use or be discarded altogether. New syllables were formed from existing syllables most morphologically similar to the "target" syllable, through transformation and combination of existing syllables. As new forms became more common, old forms declined and eventually 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 proceeds without overproduction and subsequent attrition of distinct syllable types, and does not substantially rely on improvisation and invention. Rather, syllable acquisition and changes to stereotyped songs are strongly influenced by the pre-existing syllable repertoire.

It is demonstrated that indigo buntings sing bouts of ‘‘adult plastic’’ songs (APS) distinct from stereotyped songs (SS). Some distinguishing characteristics of APS include syllables of variable morphology and syllables not present in SS. The hypothesis that APS may play a role in adult song learning is tested by monitoring socially paired males housed together. Some yearlings changed their SS to more closely match their tutors’ SS, by replacing syllables or inserting new syllables. New syllables were developed in APS through transformation and combination of morphologically similar existing syllables, and syllables were transferred from APS into SS. To address the limitations of manual scoring of spectrographs, dynamic time warping (DTW) for template-based automated analysis of continuous recordings of birdsongs was evaluated. With laboratory recordings, the DTW algorithm employed identified syllables and syllable boundaries of SS and calls of indigo bunting and zebra finch with greater than 97% accuracy. APS constituents were identified with approximately 84% accuracy. Under these restricted recording conditions, DTW has general applicability to objective analysis of birdsongs, and dramatically decreases the effort required. Application of hybrid hidden Markov models may improve the performance for variable vocalizations such as APS, and under noisy conditions of field recordings.