Figure 2.

Elliptical migration route for the Connecticut Warbler (Oporornis agilis).

This relatively common pattern of migration for songbirds concentrates them along the Atlantic seaboard during the fall migration, but more inland during the spring. This is a possible mechanism for the western extension of the range for West Nile virus in the United States.

Map courtesy of the U.S. Department of the Interior and the U.S. Fish and Wildlife Service, Migration of Birds, Circular 16 (Washington, D.C., 1998).