Irruptive Migration of Common Redpolls
The Common Redpoll is a small, brown-streaked finch with a yellow bill and a red fore-crown. It breeds in the northernmost regions of Canada and Alaska. Redpolls are irruptive migrants, meaning that their movements in winter do not follow a consistent pattern. Erratic winter movements are generally thought to be associated with the food supply. Like most irruptive migrants, the patterns of movement in redpolls during winter have not been well described. Previous research has generally been limited to small regions or time periods. In this paper, Lab scientists used Project FeederWatch data to thoroughly describe the irruptive migration of redpolls across North America in the winter of 1993-1994. The researchers found no evidence that the redpolls moved continuously throughout the winter. In other words, the birds were not nomadic. Rather, the birds simply seek out different wintering ranges in different years. However, the winter range chosen may be north of the U.S., which explains the lack of redpolls in some areas during some winters.
This article was written by Wesley Hochachka, Jeffrey Wells, Kenneth Rosenberg, Diane Tessaglia-Hymes and Andre Dhondt of the Cornell Lab of Ornithology. It appeared in the May 1999 issue of the Condor, an international journal that publishes scientific articles on the biology of wild species of birds.