Migration and Winter Ranges of Ferruginous Hawks From Washington: 2000 Progress Report

In the spring of 1999, a study was initiated to investigate the migration and winter ranges of ferruginous hawks (Buteo regalis) that breed in Washington state. We attached satellite PTT’s (platform transmitter terminals) to 9 adults and 1 nestling to monitor their longrange movements. All but 1 adult migrated across the continental divide in early fall and most hawks became localized in northwestern Montana/southeastern Alberta. Adult hawks remained at initial destinations 4 to 10 weeks. Proximal cause of migration was a high population of Richardson’s ground squirrels (Spermophilus richardsoni) along the northern Rocky Mountain front. Straight-line mean distance of migration to early fall destinations was 616 km. Hawks made at least 1 additional major movement prior to October. Three hawks migrated to the plains of North Dakota, Nebraska, and Oklahoma. Ground visits identified hawk locations in towns of black-tailed prairie dogs (Cynomys ludovicianus). Four adults migrated back across the continental divide to California. Ground visits identified these hawk locations in association with colonies of California ground squirrels (S. beecheyi). The juvenile hawk followed the same route of her mother, but moved back and forth along the migration path and covered at least 3,168 km in 69 days. We confirmed 1 adult mortality, possibly from gunshot, and another adult mortality was suspected. Satellite monitoring will continue through spring, 2000, with plans to deploy at least 4 additional PTTs.