WESTERN Bald Eagle Migration Update: April 27, 1998
Todays Report Includes:
News from Biologist Jim Watson
Washington Department of Fish and Wildlife
Journey North: Why do eagles like #16 "bother" to go so many miles north, if not to breed?
Jim Watson: There must be a strong innate drive for these eagles to return to their natal areas regardless of breeding status- this is how populations are maintained over time.
Journey North: What do you suppose non-breeding eagles do in the north during the nesting season?
Jim Watson: Since they are not breeding, of course, the primary drive is to eat. However, as eagles reach the age of sexual maturity (4-5 years) hormonal changes cause another drive...they begin to look for opportunities to occupy unfilled nesting "slots" in their natal region (i.e. due to death of adult), or exploit weaker or aging adults on existing territories by driving them out. Depending on whether the eagle population is experiencing population recovery (from contaminants, for example, in which case there is quality, unoccupied habitat) they may also seek out a mate and begin to establish a new territory in that habitat.
Journey North: When we see Eagle #16 traveling so far north--rather than staying in Washington State--it seems as if he's going "home".
Based on our movement studies of eagles monitored via satellite from Washington, movements of the 2 juveniles and 3 non-breeding adults mirrored those of the adults in terms of timing and location, but were more generalized. By that I mean, the older eagles and especially the established breeders, had shorter migration times, more consistent timing of annual movements, and more "refined" movements (i.e., flight patterns less nomadic, winter use areas more consistent between years, and returned directly to point location (i.e., home) following migration rather than wandering about their areas of origin.
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