SONG REPERTOIRE OF THE BOBOLINK - A REASSESSMENT

Previous studies have reported that male bobolinks, Dolichonyx ovyzivo rus, sing only two stereotyped song types. Here me reassess this descr iption of the bobolink repertoire, using methods of sampling and class ifying songs better suited to describing song diversity. Recording the songs of 51 males from five prairies in Iowa, we examined within- and between-individual variation for each of three levels of bobolink sin ging organization: phrases, phrase sequences and repertoires. A single song was composed of 1-15 phrases selected from about 10 locally used phrase types. Shared phrases were used with similar frequencies among different males at a locality. Two-, three- and four-phrase sequences were used repeatedly in the song variants produced by individual male s. Unlike other investigators, Ne considered each song unit composed o f a unique sequence of phrases to be a different song variant. Some in dividuals had two basic song patterns which were varied to create In a ssortment of song variants. Other individuals had repertoires too comp lex to be described by two basic patterns. Eighteen males for which we obtained samples of 20 or more songs sang between 8 and 43 different song variants. Computing an index of singing versatility derived from information theory, we found that these individuals varied considerabl y in the versatility with which they delivered their song variants. Ma les with high versatility used a greater variety of phrase transitions and repeated song variants less often than males with low versatility . This method of describing song repertoires and singing versatility p rovides the potential to test hypotheses regarding the role of the bob olink song repertoire in communication and mate choice.