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Bald Eagle Migration Update: March 26, 2002
Today's Report Includes:
- Despite His Back, Peter Nye is Back!
- How Many Days Does Migration Take? Challenge Question #10
- Interpreting Satellite Data: What Happens When Nobody's Looking?
- Try This! Challenge Question #11
- Transmitter Weights: Discussion of Challenge Question #8
- High, High Tech: The Science of Satellite Tracking
- How High? Challenge Question #12
Despite His Back, Peter Nye is Back!
"Feeling a bit better each day," wrote Peter this weekend. "It appears it will take some time." Nevertheless, directly from his sick bed to you, Peter sent the latest migration news. Thank you, Peter---but take care and get back to bed!
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Everybody is STILL staying put?Everybody except Eagle E49, that is. That eagle has already traveled back to her
nesting region, about 300 miles from her wintering grounds in New York! She made a speedy trip last week, and traveled
even faster this spring than last. (Link to Last Spring's
Migration Map and Eagle E49's Migration Data)
Challenge Question #10:
"By what date had Eagle E49 arrived in her nesting region this year? Last year? How many days did her migration take each year?"
(To respond to this question, please follow the instructions below.)
Interpreting Satellite Data
What Happens When Nobody's Looking?
By now, you're probably comfortable using satellite data to track migration.
But don't get too comfortable! Let's step back for a minute. Think about the information the satellite sends us every two days, and the assumptions we might be making when we interpret the data.
Try This!
Close your eyes. Imagine being in your classroom, day and night, with your eyes closed. Every 2 days, you blink your eyes open for a few seconds. You ONLY have that time to see what is happening. The rest of the time, you see nothing but darkness. As a class, consider the conclusions you might draw, based on your limited observations.
Think about that image when you interpret satellite data. The satellite only sends a snapshot representing a moment in time. Consider what might be happening when we're not looking!
Challenge Question #11:
"How might an eagle's behavior be different than our migration map shows? That is, what might an eagle be doing during the time the satellite is NOT sending us data? Give an example."
(To respond to this question, please follow the instructions below.)
Transmitter Weights
Discussion of Challenge Question #8
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"Seeing as how I weigh 200 pounds of lean, mean, cut muscle, my backback would weigh 4 pounds. Because 1% of 200 is 2, and that times 2 is 4," figured Jonathan at Ohio's St. Wendelin High School.
"My weight is 130 pounds so my PTT package would be 2.6 or almost 3 pounds," says his classmate Dustin.
Seventy-five pound Stephen in Ferrisburgh, VT figured that 2% of his weight is 1.5 pounds. "I don't think that it would be very heavy," he decided. "When my backpack is half full, it weighs 5.75 pounds. I went down to the nurse's office to weigh it."
"Does it hurt the birds when they have to carry around that transmitter all the time?" a student named
Holly asked Peter Nye.
"We don't think so, but it is hard to know what an eagle is thinking!," said Peter Nye. "They seem
to be able to carry it fine and go about their normal day-to-day business without any effect. The transmitters
are designed to fall off the birds after a few years. You raise a good point though, and one which wildlife researchers
constantly need to ask themselves: Is the impact on my study animal worth the information?"
Scientists do not want their research to interfere with the life of the eagle. This is for humanitarian reasons,
but also because they want to learn about NORMAL eagle behavior. How many ways can you imagine that the backpack
might cause ABNORMAL behavior? The scientists must always have this in mind when they design their research--and
when they interpret the results.
Try This!
Fill a backpack until it weighs 2% of your body weight to see how it feels. Go about your daily activities. Are
there some times that the backpack bothers you more than others?
High, High Tech: The Science of Satellite Tracking
The eagle's PTT is powered by a battery. Because the battery wears down each time it's used, the PTT can't constantly send signals. It is programmed to send a specific radio signal according to a schedule the scientist sets. For example, Nye's batteries now last for approximately 2 years if he programs the PTT to emit signals every 2 days.
The eagles' signals are picked up by polar-orbiting satellites when they pass high overhead. Just think: Zipping through space, the same satellites are picking up signals from other Journey North species-the manatees in sunny Florida, the caribou in the cold arctic, and the whooping cranes, also in Florida, poised for their first migration.
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NOAA-15 before launch |
- The satellites travel 833 km above the earth!
- Time to circle the earth: 101 minutes
- NOAA-15 was launched May 13, 1998 Vandenburg Air Force Base, CA (see photo)
- Weight at liftoff: 2,231 kg (4920 pounds)
- Length: 4.2 meters (13.75 feet), Diameter: 1.88 meters (6.2 feet)
Challenge Question #12:
"How many miles above the earth do the polar-orbiting satellites travel?"
(To respond to this question, please follow
the instructions below.)
The satellites receive the message sent by the transmitter and the transmitter's location (its latitude and longitude)
are calculated by computers on the ground. The locations are calculated using what's known as "the Doppler
shift." You've experienced the Doppler shift if you've ever listened to the shift in sound a race car or train
make when approaching and then traveling past you. (With your voice, make the high-pitched sound of an approaching
race car, then the zooming sound it makes as the car races past you, and its pitch quickly slides lower.)
According to Service Argos, the company who provides the satellite-tracking
service to scientists, "When the satellite 'approaches' a transmitter, the frequency of the signal measured
by the satellite receiver is higher than the actual transmit frequency, and lower when it moves away." This
is the basis for calculating location.
Down on earth, even if sick in bed, the scientist can access the ground-based computers and receive migration information.
"Then you guys get it - pretty cool huh?" says Peter Nye.
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 #.
3. In the body of EACH message, answer ONE of the questions above.
The Next Bald Eagle Migration Update Will Be Posted on
April 2, 2002
Copyright 2002 Journey North. All Rights Reserved.
Please send all questions, comments, and suggestions to our feedback form
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