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 phenological events for birds. The proximate causes and potential consequences of this later timing of migration should be investigated.