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THE ROLE OF HIERARCHY LEVELS IN VOCAL IMITATIONS OF SONGBIRDS

The singing of adult birds shows a clear hierarchical organization and, due to its development through vocal imitation of sound patterns, makes an excellent biological model to examine the variables that influence the imitation of patterns on different hierarchy levels, e.g., songs and elements composing the songs. We studied such variables in the nightingale (Luscinia megarhynchos), i.e., a species that in the wild uses a large repertoire of songs. Subjects were raised in the lab and tutored by presenting them with a serial learning task, here a sequence of differently patterned songs. Analyses of singing, which the trained subjects performed at the end of their vocal ontogeny, allowed us to uncover hierarchy-related accomplishments and also specific constraints in learning by imitation. Our results showed that an imitation of elements and element sequences reflected a kind of "gestalt" learning, which finally became visible in the form of specific song patterns. An imitation of song sequences, on the other hand, reflected a kind of "list" learning, which finally emerged into the formation of specific subrepertoires of song types. The structure of such subrepertoires mirrored the serial order of imitated songs but allowed, nevertheless, a serially flexible retrieval of single types of songs. These findings contribute to a better understanding of relationships between signal imitation and signal use during vocal interactions among songbirds.