Shift to Later Timing by Autumnal Migrating Sharp-shinned Hawks

Increasing proportions of Sharp- shinned Hawks (Accipiter striatus) migrated later in autumn at the Hawk Ridge Bird Observatory, Duluth, Minnesota during 1974-2009. Migration averaged about 4 days later over 35 years since 1974, and about 8 days later during late September through October in the last 16 years of the study. Our results augment previous findings demonstrating recent shifts in pheno- logical events for birds. The proximate causes and potential consequences of this later timing of migration