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Western Bald Eagle Migration Update: May
19, 1999
Special Thanks to the Bald
Eagle Biologists!
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Jim Watson
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Peter Nye
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Special Thanks to the Bald Eagle Biologists! As the migration season draws to
a close, we'd like to turn your attention behind the scenes. In addition to their
busy jobs, over the past 4 months scientists Jim Watson and Peter Nye each found
extra time to share their research and knowledge with us all. Journey North would
not be possible without the dedication of scientists like these who contribute their
expertise voluntarily. Thank you Jim and Peter!
Western Bald Eagle Migration as of 5/17/99
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Final Migration Map and Data
Eagle #12's Behavior Reveals Reasons Behind
Why Eagles Migrate
Nothing is as simple as it seems: All migratory birds don't journey northward in
the spring, for example. Eagle #12 is a case in point. She raised many questions,
because she did not do what we expected. We decided to ask Jim Watson for some answers,
before ending the season. As you'll read below, this eagle's behavior reveals the
basic reasons why eagles migrate in the first place.
Journey North: We know #12 is an adult
female. We assume she is NOT nesting locally because satellite data show she has
NOT been stationary, and because your local eagles began nesting many weeks ago.
Jim Watson: That is correct. Eagles in Washington
area have young that are 1-2 weeks old.
Journey North: Is she too young to nest?
Jim Watson: No. In fact, she exhibits the crystal
yellow eyes and pure white head and tail of an adult at least 7 or 8 years old. Bald
eagles are capable of breeding at their 4th year.
 Journey
North: Because last year she didn't head north until July, and because
she doesn't appear to be leaving now, we assume she did not nest last summer and
probably won't nest this summer either.
Jim Watson: That is correct. She has not exhibited
the kind of movements that I would expect to see if she were a territorial adult.
When adults are territorial ("territorial" meaning the adults reside on
a defended area during the nesting season) they only move within a few kilometers,
at least during the early months of spring. Eagle #12 has been considerably more
mobile than that, yet has not migrated north (reference your map). The fact that
she has resided in Washington state during the breeding season, rather than migrating
to northern provinces or Alaska, suggests she was hatched in Washington and may eventually
be recruited into the local nesting population.
The fact the she an adult but is not breeding, and that their are other adults that
are non-territorial in Washington (we call them floaters or non-breeders), is suggestive
of a healthy nesting population. Bald eagle nesting habitat will be saturated with
eagles in a healthy population, resulting in a surplus of floating adults that can
be recruited into the nesting population.
Journey North: Any comments about why she didn't
move until July last year?
Jim Watson: Two factors have probably dictated
the timing and location of her movements. Foremost, as mentioned above, is that she
is likely from a different nesting population than the other wintering eagles. They
are from the nesting population to the north, she is a local (Washington) bird. Her
movements last winter mimicked those of our local breeding population; they reside
here during the nesting season and migrate up to the coast of British Columbia to
Alaska after nesting (September, October) or earlier if their nests fail (June-August).
Because bird #12 is a non-territorial adult means that her movements, and the timing
of those movements, were similar to birds who did nest but whose nests failed. Therefore,
her drive to eat (the second stimulus) rather than nest, resulted in her northward
movement in the summer.
 Journey North: Why do these migrants go to southeast
Alaska in July?
Jim Watson: Coastal salmon, and for eagles the
all-important chum salmon, begin to spawn and die during the summer in southeast
Alaska. Salmon spawning follows progressively down the coast of British Columbia
as the fall progresses. Eagles can follow these runs southward from Alaska during
the fall back to Washington.
Journey North: What were your reasons for guessing
she'd go here to nest at this location: 55N, -130W?
Jim Watson: I did not guess that she'd NEST there,
but that she would MIGRATE there. This location, Portland Inlet and the Nass River,
were at the northern extent of her movements last year. Eagles from our study exhibit
consistent annual migration patterns for the most part, which are dictated primarily
by prey abundance. In this case, the annual chum run on this Nass River is probably
a consistent food source for migrant eagles and a good bet for #12 to check out again.
Ultimately, the availability of chum carcasses and other prey in that area, and on
surrounding rivers, will determine exactly where she goes this summer and fall.
Jim Watson
Washington Department
of Fish and Wildlife
Scientist Says: How Scientists Communicate
Research Results
One of the most important steps in a scientist's work is sharing research results
with other scientists. This is how the body of scientific knowledge is built--and
how it constantly changes as new research findings replace the old.
As a way to synthesize your learning this spring, write your own scientific paper
based on the Bald Eagle research you have witnessed----just as our featured scientists
are preparing to do!
This lesson guides you through the steps of writing a real scientific paper:
Discussion of Challenge Question #23
Eagle #18 made a bold dash northward between March 20 and April 2. He flew all the
way from Washington's Columbia River to Canada's Northwest Territories in only 12
days! We asked, "How many miles per day did Eagle #18 travel, on average?"
- Because the total distance is 814 miles (1310 km), he flew 67.83 miles per day
(109.17 km per day).
- If we estimate 12 hours of flying per day (which would mean traveling all the
daylight hours), he averaged 5.65 miles each hour (9.09 km each hour).
Please Share Your Thoughts
This is the FINAL Western Bald Eagle Migration Update. Have
a Nice Summer!
Copyright 1999 Journey North. All Rights Reserved. Please send
all questions, comments, and suggestions to our feedback form
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