Song and plumage phenotypes in a contact zone between subspecies of the White-crowned Sparrow (Zonotrichia leucophrys)

Abstract

We examined the transitions in a plumage character (lore color) and a learned behavioral character (song pattern) across a 400 -km intergrade zone between two subspecies of the White-crowned Sparrow (Zonotrichia leucophrys) in southwestern Alberta. The proportion of birds with black lores, characteristic of Z. l. oriantha, shifted gradually from over 80% in southernmost localities to less than 20% at the northern end of the zone, where most individuals had grey lores, characteristic of Z. l. gambelii. The song pattern of males also showed a complete transition across the zone, but the change was significantly more abrupt than for lore color, occurring over 50–100 km in the center of the intergrade zone. We suggest that this apparent difference in degree of introgression between the two characters may result either from differential dispersal of males and females or from switches in the song patterns of young males that immigrate into populations in which a different song type predominates. Our findings indicate that male song pattern may not be an accurate indicator of the genetic history of populations in this species.