MIGRATION ECOLOGY OF BALD EAGLES FROM AUTUMN CONCENTRATIONS IN GLACIER NATIONAL-PARK, MONTANA

During 1977-93, we studied the migration of bald eagles (Haliaeetus le ucocephalus) from autumn concentrations in Glacier National Park, Mont ana (GNP). Nonnative kokanee salmon (Oncorhynchus nerka) had attracted migrating eagles to lower McDonald Creek (LMC) in GNP since 1939. In 1987 the number of spawning kokanee declined precipitously from previo us peaks > 100,000 and by 1991 no spawning salmon were observed in LMC . The annual peak number of eagles, which had reached 639 in 1981, fel l to 25 in 1989. During 1977-88, we captured and leg banded 303 eagles ; of these, 66 also were radio tagged and 121 received patagial marker s. Patterns of migration, seasonal distribution, habitat fidelity, mar ker effects, mortalities, and foraging activities were documented. Cod e sightings (marker code read, n = 85) and marker sightings (orange ma rker reported, n = 195) came from 9 western states and Canada. Thirty- eight of 40 radio-tagged eagles wintered within the Intermountain Regi on (east of the Cascade and Sierra Nevada mountain ranges and west of the Continental Divide): 14 in Montana, 12 in Utah, 7 in Idaho, 2 in O regon, 1 in California, 1 in Nevada, and I in Wyoming. Wintering sites of individual eagles shifted as far as 660 km in different years. Win ter ranges varied from 102 km(2) to nearly 4,000 km(2). During spring migration, radio-tagged eagles followed converging routes to the GNP v icinity. Adult eagles followed a narrow corridor north through souther n Alberta and then gradually diverged to summering areas; paths of imm atures were more erratic. Thirty of 31 radio-tagged eagles summered wi thin the Mackenzie River Basin, Canada: 21 in the Northwest Territorie s (NWT), 5 in Alberta, and 4 in Saskatchewan. Distances between winter ing and summering areas were significantly different between juveniles (median = 1,480 km) and subadults (median = 2,268 km) or adults (medi an =, 2,056 km). During a 10-year period, we documented a nesting terr itory shift from Alberta to Montana (910 km) and then back to Alberta for 1 eagle. In GNP, 27% of wing-marked eagles were resighted in years after marking. Twenty-three banded eagles were reported dead (1 in Al aska). We demonstrated an eagle migration flyway connecting northern C anada's Mackenzie River Basin and the Intermountain Region of the west ern United States, All sites used by eagles throughout the flyway shou ld be highly valued and managed as part of a dynamic landscape mosaic, rather than being considered isolated habitat fragments.