Rhythm development in the zebra finch song

When we listen to the zebra finch song, the song sounds very rhythmic and repetitive. Each bird has its own song rhythm. In order to study rhythm development in songbirds we introduced a new concept to bird song research, the quantification of rhythm and periodicity in song structure. By developing a technique that gives us insights into the song rhythm we have studied how song structure changes during different stages of the zebra finch life. We found that birds trained from an early age (day 43) exhibit two types of rhythm transformations: the first type is a smooth down-modulation of rhythm during several days of song development. The second type is an abrupt transition from one rhythm to a different rhythm. Smooth transitions might be caused by a slow shift in the timing of neuronal firing, while abrupt transitions might be caused by reorganization of the rhythm generator. We also examined why is it that zebra finches that are isolated until the end of their sensitive period and then trained do not imitate well. We discovered that their poor imitation correlates with inability to add new syllables to the songs. Zebra finches that sing a long motif before the onset of training were able to imitate better than finches with a short motif, perhaps because they have more raw materials to work with. Our findings suggest that at the end of the sensitive period vocal changes still occur, but imitation is constraint at the level of song rhythm and on the level of fine temporal structure.