Migration Patterns, Timing, and Seasonal Destinations of Adult Ferruginous Hawks (Buteo regalis)

The Ferruginous Hawk (Buteo regalis) is a keystone raptor in arid-land ecosystems in western North America that is experiencing population declines in some regions. Range-wide migration patterns, destinations, and chronology of adult hawks have not been described. Between 1999 and 2014, we captured 69 adult Ferruginous Hawks east and west of the Continental Divide and monitored them ≤6 yr with satellite telemetry to document their migration ecology. During a short time (x̄ = 30 d, SD = 23) before migrating, 22% of hawks made brief movements away from territories (x̄ = 211 km, SD = 133) and then returned. Migrating hawks (98% of 89 analyzed patterns) moved across broad fronts using five different strategies in three distinct periods: summer (July–August), fall (September–November), and spring (February–March). Breeding range longitude and latitude strongly influenced (r = 0.78) timing of summer migration that was directed to focal areas shared by breeding populations of hawks in the Northern Grasslands and Central Plains. Hawks nesting in grasslands from Canada to the Southern Plains demonstrated a strong pattern of southward migration to summer and winter ranges along the east front of the Rocky Mountains to central Mexico. Hawks from shrub-steppes in the Columbia Basin and Great Basin migrated eastward to summer ranges across the Continental Divide to grasslands, then to wintering areas in California and northern Mexico. On average, adult hawks spent 64% of the year away from breeding home ranges and migrated 2376 km (SD = 1165) annually, but differences in migration destinations, distance (P = 0.048), and duration (P < 0.0001) among populations potentially exposed them to variable levels and types of stressors. Accordingly, conservation of nonbreeding habitats used by Ferruginous Hawks is important for maintaining health of breeding populations; conservation efforts should emphasize protection of fossorial prey and habitats on shared summer ranges and winter ranges in the Mexican grasslands and Central Valley of California.