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WESTERN Bald Eagle Migration Update: April 6, 1998
Today's Report Contains
- News from Biologist Jim Watson
- Satellite Data from WESTERN Eagles #05, #12, #13, #16
- Challenge Question #10: Guess the Nest
- Migration Routes to the North: Interview With Jim Watson
- Announcement: Watch for Weekly Data Updates
News from Biologist Jim Watson
Here's the news we've been waiting for:
"Birds #12 and #13 have not left Washington--but #5 and #16 are on their way home! Eagle #05 was in southeast Alaska yesterday, and #16 is on the McKenzie River by Great Slave Lake," reports Watson.
Latest Satellite Migration Data
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Latest Travels of Western Eagles |
WESTERN EAGLES
Notice how many miles Eagle #16 flew last week, between March 24th and April 3rd! But how do you interpret the
news that haven't left Washington yet? What are the possible reasons? Take a look at the migration data below,
and read today's interview with Jim. Then see if you think you know where ALL the eagles intend to nest this season:
Challenge Question #10: Guess the Nest
Where do you think our WESTERN eagles' nests are located? Be sure to give the exact latitude and longitude for
each eagle's nest.
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Eagle |
Lat (N) |
Long (W) |
| #05 | ||
| #12 | ||
| #13 | ||
| #16 |
(To respond to this question, please follow the instructions at the end of this report.)
Migration Routes to the North
Interview With Jim Watson
We interviewed Jim about the routes the eagles are taking. Here's what he had to say:
Journey North
Would you comment on the 2 routes your eagles seem to take, the coastal & the interior corridors?
Jim Watson
Both migration corridors provide ample opportunities for eagles to feed as they move to and from breeding areas. Inlets and rivers on the coastal route provide seabirds and fish, such as salmon, in the fall, and herring in the spring and summer. The Fraser River and its tributaries on the interior provide salmon in the fall, but also a variety of other fish and birds throughout the spring.
The coastal migration route is a logical flight corridor for eagles nesting in southeast and interior Alaska, and northern Yukon Territory. However, we also had 2 eagles in the spring of 1997 that flew up the coast to southeast Alaska, and then back east to interior British Columbia and Northwest Territories.
This may have been a result of the fact that lakes and rivers in the northern interior were still be frozen by late March--by using the coastal route, these eagles can get a good part of their migration done, and by the time they reach southeast Alaska waterways are thawed out in the interior. For eagles nesting in central and southern British Columbia, the interior route is closest to their breeding areas.
Journey North
How is food availability different/same? Why?
Jim Watson
There may be some differences in food availability (how much is available to eat) along these flight corridors, but nobody has collected or compared this information since that would be difficult. Notice that the coastal route probably provides marine fish, seabirds, and even marine invertebrates (i.e., crabs, oysters, clams) to migrating eagles, whereas the Fraser river and associated lakes and streams provides freshwater fish, waterfowl, and mammals to migrating eagles. The fact that these routes both provide food makes them more attractive to migrating eagles than flying over land.
Journey North
What other factors might influence the route they take?
Jim Watson
Whether or not the eagle is a breeder and has a specific location to return to is likely a key factor determining the exact route the eagle uses in migration. If the bird is not breeding, the presence of other migrating eagles likely influences where and when it moves. However, even non-breeding eagles eventually return to their natal areas as we have seen from studies in Washington. An eagle's choice of the exact route it takes is certainly influenced by the local topography and prevailing winds on a given day. Ideally, these factors will allow the eagle to fly on "cruise control" and expend less energy.
Journey North
Is this a learned pattern, so that maybe populations of eagles go along
certain routes?
Jim Watson
There probably hasn't been enough research done to say for sure how much of an eagle's directional sense is learned and how much is innate. However, it seems that juvenile eagles during their first migration have a definite sense of which direction to fly. In Washington, we found that juveniles migrate north from the nest area without the adults. After they leave the nest area, they probably follow other eagles as they migrate through the same area. Over time, these younger eagles likely remember the flight route from visual cues, much the same as we do when we take our annual vacations.
It would be an interesting experiment to take an eaglet out of a nest in a northern latitude where the breeding
eagles migrate southward (i.e., Yukon Territory), and place it in a nest in Washington where the breeding eagles
migrate northward. Would the eaglet migrate south or north when it fledged?
Journey North
Do individuals go same route each year?
Jim Watson:
For the 4 eagles we monitored this spring and last spring (including #5 and #16), the eagles have followed the
same routes both years.
Journey North
Do eagles fly with their mates? Or with other related eagles?
Jim Watson
I am unaware of any study that has tracked both adults from a territory from breeding to wintering areas and back
to the breeding area. We've observed some nesting activity by migrant eagles in spring before the moved north,
and similar activity was observed in Colorado. In general, when we see eagles migrate north from territories
in Washington, the adults do not leave on the same day. It seems unlikely they fly together, although they may
end up on the same wintering area. As I mentioned above, juvenile eagles are independent once they migrate from
their natal area and don't have any association with the adults after that time. The juveniles we have followed
returned the following summer to within a few kilometers of their natal area, but not to the nest site.
Announcement: Watch for Weekly Data Updates
Since the eagles are now on their way, we'll post a quick data update each Monday so you'll have the latest news. Watch for the next update on April 13, 1998.
How to Respond to Today's Challenge Question
1. Address an e-mail message to: jn-challenge-eagle@learner.org
2. In the Subject Line of your message write: Challenge Question # 10
3. In the body of your message, answer today's question.
The Next Bald Eagle Migration Update will Be Posted on April 13, 1998.
Copyright 1998 Journey North. All Rights Reserved.