Song clustering by meadowlarks: Is it related to repertoire size?

Some birds with song repertoires sequentially associate (or cluster) songs of different types. That is, certain song types may occur together repeated ly, even on different days. We determined whether clustering of meadowlark songs correlated with repertoire size. We also tested whether clustered son gs reflect either their structural similarities, or dissimilarities. Our da ta were obtained from recordings of free-living individuals of two meadowla rk species, eastern, Sturnella magna, and western, S. neglecta. Eastern mea dowlarks have approximately 10 times more song types per bird than do weste rns. Therefore, if clustering is related to repertoire size, we predicted t hat there should be (1) proportionately more song clusters in eastern meado wlarks than in westerns, and (2) a similar correlation across individual bi rds within a species, especially so in easterns, which have a broader range of repertoire sizes. All 14 easterns examined showed clusters whereas only 5 of 11 westerns did so, and the easterns had proportionately more per bir d. Many of the same clusters occurred in different recordings of individual easterns. In easterns, the extent of clustering as measured by a PCA analy sis correlated strongly with estimated repertoire size. Clustered songs wer e neither more similar in structure, nor less so, than randomly-paired song s.