Geographic patterns of song similarity in the Dickcissel (Spiza Americana)

Song sharing among neighboring males is a well-known, frequent outcome of song learning in oscine passerines and some other groups, but only limited investigations of the spatial scale of this phenomenon have been pursued. Oil the basis of recordings of 1,043 individuals, we investigated song sharing in Dickcissels (Spiza americana) at local and regional scales at sites from northern Kansas to northern Oklahoma. Classification of song elements revealed decreasing song similarity with increasing distances between individual birds at small to intermediate scales, to similar to 10 km. At the largest spatial scales (10-300 km between sites), there was very little similarity among sites and no obvious tendency for a decrease in similarity with increasing distances among our 30 sites. At our intensively sampled site, analyses of quantitative measurements showed that, at least for our most widely shared song element, frequency and duration were more similar in closer birds. Thus, distance between birds influences both quantitative and qualitative song similarity in Dickcissels. Variability existed among sites in the shape of the song-sharing decay Curve, which indicates that other factors besides distance also govern song-sharing patterns. We found high repeatability of individual songs for both second-year (SY) and after-second-year (ASY) mates throughout the season, and high conformity to the local song neighborhood in both SY and ASY males from their first recording soon after arrival in May. Returning ASY males sang the same song they had produced the previous breeding season. Received 4 October 2007 accepted 7 June 2008.