Vocal Dialects and Gene Frequencies in the Chingolo Sparrow (Zonotrichia capensis)

Zonotrichia capensis, known in the literature as the Chingolo, Andean Sparrow, and Rufouscollared Sparrow, is one of four species of the genus Zonotrichia, all confined to the New World. The Chingolo is a small songbird that ranges from Tierra del Fuego to the Mexican state of Chiapas, and has also colonized the Caribbean islands of Santo Domingo, Aruba, and Curagao. This species is distributed over 6400 km of latitude, and 4800 km of longitude, from sea level to 5000 m of altitude. Within this extraordinary range, Chapman (1940) recognized 22 races. The Argentine provinces of Buenos Aires and Tucuman, where the present study was conducted, fall within the range assigned by Chapman to Z. capensis hypoleuca. Neighboring populations of Z. capensis frequently differ in the characteristics of their song. When these differences are marked and systematic they give rise to dialects (Nottebohm 1969). Over vast areas of pampas country, the dialect of the Chingolo remains unchanged. But where life-zones change over short distances, as in altitudinal transects, dialects also change over short distances. This observation suggests that song dialects in this bird may have evolved to reduce gene flow between neighboring populations experiencing different selective pressures. Females born in a given dialect area would breed in that dialect area and choose as mates males with a song that matched that dialect; males, in turn, would learn to sing the dialect of their birth area (Nottebohm 1969, 1970). To test this hypothesis, it is necessary to evaluate the genetic differences that may exist between neighboring populations with different dialects, and to compare them with differences between samples of neighboring populations having the same dialect. Measures of gene frequencies have been used in the past to evaluate the degree of gene flow between segments of rodent populations (Selander 1970; Selander et al. 1971), but the present report is a first attempt to correlate vocal and genetic differences among populations of a songbird species. Though the results presented here do not permit a final assessment of the influence of song d alects on gene flow, they constitute the first report of simultaneous measurements of allelic and dialect characteristics of avian populations.