Geographic Variation in Syllables of House Finch Songs

Bird songs often can be described as strings of individually distinct units called syllables. Toward furthering our understanding of the processes and consequences of vocal learning, geographic variation in vocalizations may be as important at the syllable level as it is at the song level. To examine geographic patterns of song variation at the syllable level in House Finches (Carpodacus mexicanus), we analyzed the syllable repertoires of 91 males at 21 sites in northern Colorado. Analyses were performed and comparisons were made among individual birds within and between sites. Using Jaccard's similarity coefficient, we determined that syllable sharing among birds was significantly greater within sites and among sites less than 5 km apart than at greater distances. Within a site, any two birds usually did not share the majority of their syllable types, but discriminant function analysis showed that approximately 63% of the birds possessed syllable repertoires that matched most closely those of other birds at the same site. Less than 5% of the birds sang syllables that most closely matched those of birds at a site more than 20 km away. Our results suggest that House Finches in northern Colorado exhibit localized syllable sharing and that syllable sharing decreases exponentially with distance, but we found no evidence for discrete syllable dialects. Geographic variation in bird song typically has been evaluated using whole songs. Depending on how birds assess the singing behavior of other individuals and perceive differences in songs, it may be important to examine geographic variation and population differences at the syllable level as well.