Song organization of House Finches at the edge of an expanding range

Colonization patterns of House Finches (Carpodacus mexicanus) provide a rare opportunity to study regional differences in songs associated with differences in colonization histories. House Finches have undergone two different types of colonization events in the mainland United States which have given rise to differences in singing among three regions. In this study, I describe songs of House Finches that have recently colonized southeastern Wisconsin at the western edge of their expanding eastern range. Song stereotypy, repertoire size, and song sharing patterns in Wisconsin differ from those of eastern and western House Finches. An earlier House Finch colonization of the East Coast, by the parental West Coast stock, resulted in an increased rigidity of song syntax, decreased repertoire size, and increased song sharing. Colonization of Wisconsin by East Coast stock, however, has]ed to a decreased rigidity of syntax, increased repertoire size and decreased song sharing. The two colonization events differ markedly in the numbers of founders and the size of the area from which potential colonizers may have originated. Differences in singing between these two areas may have been influenced by the amount of heterogeneity of song types present during the early stages of colony establishment.