Partial migration and wintering localities of American kestrels nesting in the Pacific northwest

Abstract

Based on banding recoveries, an estimated 89.5% of American kestrels (Falco sparverius) nesting in eastern Oregon, eastern Washington, and Idaho (excluding the Snake River Plain) are migratory and primarily migrate to western Mexico for the winter. Band recoveries from Mexico may be biased; however, we do not know whether the bias is toward more or fewer recoveries. The banding data imply that the remaining kestrels from the region (10.5%) are permanent residents, and we found 2.8% of a northeastern Oregon population on nesting territories in January 1981 (permanent residents). A higher percentage of the nesting population appears to be permanent residents in the valleys along the Snake River Plain than in the remainder of Idaho, eastern Oregon, and eastern Washington (p = 0.02). Limited evidence shows that permanent resident kestrels in eastern Oregon nest earlier than migrants. Information available for the population west of the Cascade Mountains in Oregon and Washington was limited.