TEMPORAL PATTERNING OF WITHIN-SONG TYPE AND BETWEEN-SONG TYPE VARIATION IN SONG REPERTOIRES

In many songbird species, males sing a repertoire of distinct song typ es. Song sparrows typically are described as having repertoires of abo ut a dozen song types, but these song types are themselves quite varia ble and some songs are produced that appear intermediate between two t ypes. In this study we quantify the similarity between successive song s produced by song sparrows in order to determine if differences betwe en song types are emphasized or deemphasized in bouts of continuous si nging. In spite of the high degree of variation within song types and similarity between song types observed in this species, we show that t ransitions from one song type to the next are distinct as compared to transitions within sequences of the same type (Figs. 4 and 5). Variati on does not ''accumulate'' across sequences of the same song type, and the average variation observed within a continuous sequence of the sa me song type is significantly less than is predicted from the total va riation recorded for that type across many different bouts (Fig. 6). T hese results support the view that song sparrows include two levels of variation in their singing: differences between song types as is comm only observed in species with song repertoires, and an independent lev el of variation observed for songs of the same type.