S. Nowicki et al., TEMPORAL PATTERNING OF WITHIN-SONG TYPE AND BETWEEN-SONG TYPE VARIATION IN SONG REPERTOIRES, Behavioral ecology and sociobiology, 34(5), 1994, pp. 329-335
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.