This thesis investigated the use of song repertoires during territorial defense of the song sparrow, Melospiza melodia. The functional and adaptive significances of repertoires in the order Passeriformes were reviewed. Within the family Fringillidae, an examination of repertoire size and life history features of different species revealed no significant correlations. / Observations of six neighboring song sparrows yielded information about the relative uses of repertoire-dependent and repertoire-independent mechanisms in coordinated song interactions, as well as in signalling agonistic probabilities. The behavior of song switching, independent of the identities of song types, was found to most effectively perform both types of functions. / A series of playback experiments tested and supported the hypothesis that the song sparrow's rate of switching song types increases with agonistic stimulation. Song versatility, rather than switching rate per se, was found to be an appropriate agonistic stimulus.

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