Two morphologically distinct subspecies of the Australian Ringneck Parrot (Platycercus zonarius) meet in a zone of hybridization in southwestern Western Australia. Individuals produce a flight call, a learned vocal signal used by a mated pair to maintain contact and coordinate their movements. I asked how the learned vocal signal covaried geographically with morphology. Across the distributions of the parental taxa and within the hybrid zone, I tape-recorded 398 birds in 38 locations and scored plumage traits. I found that the parental taxa exhibit a discrete difference in their flight calls, but within each of the parental taxa there also were local dialects. There were dialects in the hybrid zone as well, where individuals at a site shared the same type of flight call whether they displayed plumage phenotypes of parental taxa or of hybrids. In the hybrid zone, populations tended to have a form of the flight call intermediate between parental taxa, though the form of the call was more strongly influenced by introgression of call characteristics of one of the parental taxa. These results support both a cultural-dominance model and a blending model of cultural interchange. The parental taxa are hypothesized to have resulted from Pleistocene isolation in refugia during a severe arid period about 25,000–15,000 years ago, with subsequent expansion to create the observed overlap zone. My data suggest that the phylogenetic trace, evident in the culturally transmitted vocal differences of the contemporary parental taxa, originated in the remote past and has been retained for many generations.
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Vol. 125 • No. 3