Bald Eagle

Bald Eagle

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Bald Eagle Migration Update: March 6, 2001

Today's Report Includes:

March is Migration Month!


Winter Range Map
This Week's Satellite Data

If past years are any clue, the first eagle should move out of New York any moment. However, at the moment, a huge Nor'easter is blasting the East Coast. Up to two feet of snow are predicted in New York, and schools across the state are closed. When the storm clears away, which eagle do you think will be the first to move?
Try This! Do Eagles Migrate at the Same Time Each Year?
Take a look at migration records from last spring and predict when each eagle will take off this year. Peter Nye is doing the same thing right now!

Challenge Question #6
"By what time last spring had each of the eagles begun to migrate: Eagle F43, F81, K58, K70 and K72?"

(To respond to this question, please follow the instructions below.)

Field Notes from Peter Nye

Two New Eagles Now Online: Welcome to Eagle E49 and E63

Hi Kids,
We've continued our trapping and with great success! Since our last update, two more birds have been captured, Eagle E49 and Eagle E63, for a grand total of 8 eagles. Eagle E63 is our 2nd male--do you think male and female eagles migrate at different times? I hope you enjoy the capture stories of our latest Eagles:
  • Link to Full Story of Capture of Eagle E63
    "He was perched atop the main carcass, head down and feeding actively. I told Amy, 'Pull!!' A loud bang and huge cloud of smoke instantly covered the trap site and all its occupants as the net deployed."

  • Link to Full Story of Capture of Eagle E49
    "This time, we took a slightly different approach in our trapping effort because we were after two particular Eagles. Instead of spreading a number of traps around an area we spent three days studying these birds' habits until we found a pattern we could use."

We are excited to see where these eagles will go this spring, and hope you are too!

Until next time,
Peter Nye

Male or Female?
When capturing Eagle E49, the biologist said, "It's hard to say if this Eagle was a male or female. Usually you can tell because female Eagles..." How would you complete this sentence?

Challenge Question #7
"The plumage of adult eagles is identical. What other clues do you think scientists use to determine if an eagle is male or female? List as many visual--and behavioral--examples as you can."

(To respond to this question, please follow the instructions below.)

Discussion of Challenge Question #3
Home on the Range
"Based on one month's data, which eagle seems to have the largest home range?", we asked.

Iselin Middle School's 7th grade students said, "We believe eagle F81 has the largest home range. It flies 125 miles from East to West and 40 miles from North to South."

F81's Winter Range
(Click for larger image.)

Great job in measuring! It's interesting to note that Eagle F81's behavior changed during the second month of data. In fact, between February 6th and March 2nd, the greatest distance between any two points of travel was only 15 miles. What a contrast with the 125 miles he spanned in January! So far, we've learned that different eagles have different sized home ranges. We also know that we might think an eagle's home range was larger or smaller depending on when we measured it. The added information F81 provided this month shows how flexible scientists need to be in their thinking. Reassessing is an important step in the process of science.
Discussion of Challenge Question #4
Human Home Range
"How does an eagle's winter range compare to your own? How much of your home range do you consider to be your territory?"

"I consider my room to be my territory," begins Timmy of Plano, TX. "It is about 12' by 12'. My winter range is normally about 15 miles by 15 miles with a trip north to my Grandma's at Christmas of 1000 miles. My normal range is smaller but I travel further north from my comfortable climate in my side trip than the eagle does."
Discussion of Challenge Question #5
Why Do Talons Beat Beaks?
In our last update we asked, "Why do you think eagles carry their prey with their talons instead of their beaks? List as many good reasons as you can."

Journey North students came up with at least 14 different reasons! Here are three answers from bird expert Laura Erickson, followed by the terrific ideas students provided:

Eagle Eyes: All the Better to See You With!

People often say that eagles and other birds see farther than we do. How can that be? After all, we humans can see the sun 93 million miles away and stars thousands of light years away with our naked eyes!

But let's come down to earth. When a person looks down from the Sears Tower in Chicago, cars below appear as tiny as bugs, and we can barely see the people. If a Bald Eagle looked down from the same height, scientists think it could spot a mouse on the sidewalk below! So when we say birds see farther, we mean that at a given distance, they see things in much greater detail.

Eagle eyes have several features that give them clearer vision than humans have. One is the little spot in the retina called the fovea. Primates including humans, and all birds, have a fovea. Here the light sensitive cells (called rods and cones) that actually enable us to see are VERY concentrated. When a person or eagle is looking at something, we turn our head and eyes so that the light from the image hits our fovea.

These little cells are in some ways similar to the tiny dots (pixels) on the screen of your computer monitor. Humans have such great vision because our fovea has about 200,000 rods and cones packed into each square millimeter of the fovea. But eagles have over a MILLION rods and cones in each square millimeter of their fovea!! That's about the same number of visual cells as the finest computer monitor has on its entire screen when set at its highest resolution. The resolution for a person would be similar to setting a computer's screen at a much lower resolution.

Challenge Question #8
"A person with good vision should be able to see a mouse at about 200 feet. Based ONLY on the number of rods and cones in the fovea, from how far away do you think an eagle could see that same mouse?"

Eagles can't read an eye chart to show us how good their vision is. So how does anyone know!?

Challenge Question #9
"How do you think scientists evaluate how good an eagle's eyes really are? (Clue: Think about eagle behavior and anatomy."

How to Respond to Today's Challenge Questions:

IMPORTANT: Answer only ONE question in each e-mail message.

1. Address an e-mail message to: jn-challenge-eagle@learner.org
2. In the Subject Line of your message write: Challenge Question #6 (#7, #8 or #9).
3. In the body of EACH message, answer ONE of the questions above.

The Next Bald Eagle Migration Update Will Be Posted on March 20, 2001

Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form

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