First-year migration and natal region fidelity of immature ferruginous hawks

Abstract

From 1999 to 2014 we used satellite telemetry to address knowledge gaps in the migration of juvenile Ferruginous Hawks (Buteo regalis) related to their migration independence from adults, migration patterns, and locations of settlement ranges. Nine fledgling hawks migrated independently from their radio-Tagged parents, left natal areas at different times and directions, and settled on summer ranges separated from parents by an average of 592 km. Juvenile hawks that we followed through their entire first year (n = 12) travelled about three times farther and twice as long as adults during annual migrations, and arrived an average of 11 to 38 d later on summer, winter, and spring ranges. Hawks that hatched west of the Continental Divide (n = 14) migrated northeast in summer to ranges in the northern grasslands and to winter ranges in California and the Great Plains. Hawks that hatched east of the divide (n = 17) also migrated north to summer ranges, but wintered south from the Central Plains to Mexico. At the end of their first year, hawks (n = 14) settled on spring ranges within their natal regions, an average of 350 km from their hatch locations. In their third spring, hawks (n = 6) settled an average of 123 km from hatch locations and two females nested. We ascribe differences in migration distance and timing of juvenile hawks relative to adults to juveniles' inexperience in locating suitable feeding areas and range prospecting independently from parents. Because migration patterns and regional fidelity of juvenile Ferruginous Hawks to settlement ranges were similar to those exhibited by adult hawks, the protection of fossorial prey and their habitats on seasonal ranges that promote survival of adult hawks will afford the same benefits to the juvenile cohorts.