SEWALL, K.B.; HAHN, T.P.; University of California, Davis; University of California, Davis: Differential Heterospecific Mimicry in Three Species of Cardueline Finches

Vocal mimicry has been documented in a number of oscine taxa. However, the prevalence and function of heterospecific mimicry in bird song remain unclear. We sampled songs from 15 individuals each of three Cardueline finch species in the genus Carpodacus in a comparative study of vocal mimicry. Using acoustic and spectrographic techniques, we assessed both the number of heterospecific sounds mimicked by each male and the frequency with which heterospecific signals were incorporated into the birds’ songs. Cassin’s finches (C. cassinii) and purple finches (C. purpureus) incorporated numerous heterospecific imitations into the middle and end of their warbled songs, and Cassin’s finches occasionally produced long songs composed almost solely of imitated sounds. Though mimicry has been documented in house finches (C. mexicanus), the individuals we examined did not incorporate any recognizable heterospecific sounds into their vocalizations. Further, in the only record of heterospecific mimicry in a house finch, the bird inserted an imitation at the beginning of the song. This suggests a qualitative difference between the imitation process in Cassin’s and purple finches, versus house finches on the rare occasions when it does occur. These observations, coupled with the phylogenetic relationships among the three species, suggest that heterospecific vocal mimicry evolved in this group with the division of the Cassin’s / purple finch lineage from the house finch lineage, about 9 mybp. At this point, vocal mimicry appears to be a normal aspect of song in Cassin’s and purple finches but only occurs as an anomaly in house finches. The functional significance of mimicry in these three species should prove an interesting area of future study.