The Bell's Vireo subspecies is restricted to coastal California where it was once widespread, and is now Federally Endangered. A number of Important Bird Areas that support the species have been identified by Audubon California. These include the Santa Margarita River/Camp Pendleton IBA which holds the largest population in the state (300 pairs), the San Luis Rey River IBA (200 pairs), and the San Pasqual Valley IBA (150 pairs). Surprisingly little is known about the species wintering range, which extends along the Pacific coast from northern Mexico south to northern Nicaragua. (From Audubon Watch List)