What the eagles tell us

As birds of prey, and especially eagles, are top predators in their ecosystems, studying their populations gives us information about changes in their habitats and threats to their (and ultimately to our) survival.

By studying the age-structure of migrating Golden Eagles, we can accurately measure the breeding success (and hence food availability) of the birds in Alaska and The Yukon. It can also tell us the survival rate of young birds in northern Mexico and southern United States, and this indicates the health of their wintering environment.

Satellite telemetry of birds originating in Denali National Park in Alaska (conducted by the US Department of the Interior: Carol McIntyre) has proved the long distance nature of the migration, with some birds moving as far as northern Mexico for the winter.

Comparison of age ratios of fall migrants with those of the succeeding spring migration gives us information on the survival of juvenile birds on their winter ranges.

Study of median passage dates (the date on which 50% of birds of a population has passed) is demonstrating long-term changes to the climate of western North America.

As the Golden Eagle is one of the top predators in its breeding and wintering ranges, any significant change in these environments will be reflected most rapidly in such predators. Because of the long-term nature of the database, it has also been possible to demonstrate the apparent cyclic nature of the movement, probably tied to Arctic mammal and bird prey species cycles.

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