Bald Eagle

Bald Eagle

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Western Bald Eagle Migration Update: March 24, 1999

Todays' Update Includes:

Field Notes from Biologist Jim Watson

To: Journey North
From: Jim Watson

Hello Students:
Spring is definitely sprung in western Washington. We actually had 2 sun-filled days this week! There are 4 pairs of resident bald eagles that nest just downriver on the Skagit River. Yesterday I noticed that 2 of them were incubating eggs. Washington has over 600 pairs of eagles that nest in the state.

Why Don't All Eagles Migrate?
That brings up some interesting points to ponder...why do these eagles remain to nest in the state, yet other eagles in our telemetry study migrate from Washington after winter to nest in other places? Or, a better way to ask this question is, why do eagles that nest in Washington remain here throughout most of the winter, while migrant eagles move into
Washington to winter? Discuss this as a class before you read on!

Some breeding populations are located in areas that are inhospitable in the winter and don't provide adequate prey due to the freezeup of lakes and rivers. These birds have to migrate to other areas in order to eat in winter. The relatively mild climate--and abundant chum salmon on the Skagit River--provide ideal winter habitat for these eagles. But because there is limited nesting habitat in Washington, these eagles move back to their breeding areas after winter.

Satellite Data from WESTERN Eagles
Time to check in with our 2 telemetered eagles. Finally, some action!

Winter Range as of 3/20/99

Eagle #18 has shown a definite movement from the winter area. Based on where this bird is located now, you can see the "flight corridor" he used to move from the previous location. Rather than flying over barren land, he flew along a "logical" landscape.

Challenge Question #11
"What 'logical' landscape did Eagle #18 fly over? Why do you think he flew along this corridor? Where might you expect him to fly in the upcoming weeks, based on this early movement?"

Eagle #12 has not shown the same type of movement at this point. Based on my discussion above, do you think she could be nesting in Washington?

Challenge Question #12
"Do you think Eagle #12 could be nesting in Washington? Why or Why not?"

(To respond to these questions, please follow the instructions below.)

Eagle Killed After Deep Snow Strands Moose
Finally, a followup report on the downed, telemetered eagle I reported on during the last update. It turned out the bird was an eagle that was doing very well until she was hit by a car near Prince Rupert, British Columbia, on the 24th of February. (See if you can find this town on a map 54.30N, 130.50W.) She was feeding on a road-killed moose with other eagles when she was killed. Evidently, the deep snow in that area stranded many moose on the highways and railroad tracks and provided a lot of carrion for eagles. I recovered the carcass and transmitter last week and was pleased to see that, except for some feather wear under the transmitter, she had worn the package quite well. Although it is unfortunate that she died, the fact that she had a transmitter on allowed me to identify where she was and how she died. Technology came through!

Good tracking until the next update,

Jim Watson
Washington Department of Fish and Wildlife
Discussion of Challenge Questions #9 and #10
In his last update, Jim Watson explained that the size, shape and
attachment method (backpack harness) of satellite transmitters were
developed to minimize their effects on an eagles. Aside from concern for
the individual eagle's health, this is important because he investigating
the natural, uninhibited movements of these eagles.

Challenge Question # 9 asked, Think of one way that a transmitter might
affect an eagle's health or behavior if it were: 1) too heavy; 2) too large
(surface area); or the harness too tight or loose. Here are Jim Watson answers:

If a transmitter were:
  • too heavy it might impede flight, access to food, health and hence survival;
  • too it might impede flight, particularly long migrations, when wind resistance and air flow over an eagles flight surface is critical;
  • too large it might also hinder mating [for female];

If a harness were:

  • too tight it might cause abnormal feather wear or pressure sores;
  • too loose it might cause shifting in the transmitter resulting in feather breakage, awkward flight, and perhaps most importantly increased opportunity to get snagged on a branch.

Discussion of Challenge Question #10
"If you wore a backpack that weighed 2% of your body weight, how heavy would your backpack be?"

Eagle with Satellite Backpack

Here are the calculations from Ms. Thurber's class in Vermont, "Betsy says that her backpack would weigh 1.16 pounds. That's because she weighs 58 pounds and 2 percent would be that much. Heather's backpack would weigh 1.94 pounds because she weighs 97 pounds. Heather's real backpack weighs a LOT more than that! Both of these girls are Girl Scouts - Two boxes of Girl Scout cookies would weigh almost a pound. Betsy discovered that her favorite reading book and a box of Girl Scout cookies weighed exactly a pound." (

And from our Bald Eagle trackers in Ontario: " If I had a backpack that weighed 2 % of my body weight, it would be 2.288 kg (Tyler--52 lbs) and it be 2.728 kg. (Kyle weighs 62 lbs.)" Scott Young Public School (
How to Respond to Today's Challenge Questions

Please answer ONLY ONE question in EACH e-mail message.

1. Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question #11
(or Challenge Question #12)
3. In the body of EACH message, answer ONE of the questions above.

The Next Bald Eagle Migration Update Will be Posted on April 7, 1999.

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