Call learning in black-capped chickadees (Parus atricapillus): The role of experience in the development of 'chick-a-dee' calls
The role of learning in the development of bird vocalizations other than territorial song is not well studied. The well-known role of direct imitation in the development of territorial song potentially masks the effects of other processes in the development of vocal behaviour. The 'chick-a-dee' call of black-capped chickadees is a good system in which to investigate more subtle developmental processes because this call is composed of a small number of distinctive note types. These note types may be classified objectively based on a simple set of acoustic variables, allowing for a quantitative assessment of vocal learning. We raised four groups of black-capped chickadees under different degrees of social and acoustic isolation. We then used a multivariate analysis of the acoustic structure of the introductory call notes ('A-' 'B-' and 'C-notes') to determine how similar the notes produced by these hand-reared birds were to the notes of wild birds. Hand-reared chickadees with greater exposure to normal phonology produced notes of all three note types that were more similar to those of wild birds. Regardless of experience, however, all birds produced A-notes that fell within the normal range of those produced by wild birds. By contrast, the development of normal B- and C-notes appears to be more dependent upon experience. These data suggest that learning may play a different role in the development of different phonological units within one vocalization. Our results also illustrate the importance of considering processes other than simple imitation in the development of avian vocalizations.