Bald Eagle

Bald Eagle

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Eastern Bald Eagle Migration Update: February 22, 2000

Today's Report Includes:

Field Notes from Biologist Peter Nye

Home on the Winter Range

Winter Range Map
as of February 18, 2000

"At last! Glad to see that Eagle #F81 is finally 'home'! It took until February 16 for him to return to the area he occupied last year. In contrast, notice how Eagles #F43, #F83, and #K70 have been staying within their wintering/capture areas?

Today's Satellite Data

This is just what we expect, especially from older birds. But Eagle #F81 has not exhibited the same fidelity to his wintering area as the other birds have. It may be that he is a young and unattached male. Perhaps he's still kind of floating around, trying out different areas, and has not yet settled on a 'permanent' wintering site. (Or breeding site for that matter. If you study his spring/summer 1999 movements, those also look like a young, unmated bird without a definitive breeding territory yet. The locations are not in a tight cluster like many of the others. Rather, they're scattered over time and range.)

Discussion of Challenge Question #1
"By the way, Eagle #K70 was captured in the St. Lawrence River on Wellesley Island, which is one of the larger Thousand Islands. So all the students who figured 'Thousand Islands' had a pretty good answer! She has been staying very local to the capture area except for her minor southern junket to the interior on 2/16. It'll be interesting to see how long she stays around there. Likely just a short 'visit', then back to the river. We'll see.
Research Goals: Information for Protecting Eagle Habitat
"We are trying to learn several things from these studies that are of great importance to us. First, we want to identify critical night-roosting, daytime feeding and daytime perch areas for these eagles. Such habitats are of vital importance to our wintering eagle population. Armed with the knowledge of what habitats these birds use, we can then determine if they are threatened and might be lost--and then try to protect them if need be. Today's map gives a good indication of the areas these 4 eagle are using.

"We're also trying to locate similar critical habitats along the migration routes and on the breeding grounds of these eagles. We have learned that many NY wintering birds are coming from similar areas in Canada, breeding areas that may not be known by the Canadian and Provincial governments, and that might also need protection.

"And finally, because we have satellite radios that can operate for multiple years, we are learning about "fidelity" to these sites and routes. That is, how faithfully do these eagles use their wintering areas, migratory routes and nesting areas year after year?
Nye's Surprises About Fall Migration
Discussion of Challenge Questions #2 and #3

"Challenge Question #2 asked, What did you learn about 'fall migration' that surprised you the most?

"I expected these birds to come back down to their wintering areas as in the past, more based upon calendar timing (amount of daylight) than anything else. This they didn't do. As you know, Eagle #F81 didn't complete his "journey south" until last week. Eagle #F43 arrived back in NY on 8 January in 1999, but not until the 21 January this year. Other adult eagles begin arriving back in New York in November and December--so there is quite a range in their arrival dates overall.

"Why do some birds travel at different times than others? We don't yet have all the answers! I suspect much is related to: where they are coming from; the amount of open water (and thus fish and the eagle's ability to survive); if the winter is very mild, as ours was here in the East until mid-January, travel dates will be affected. In such situations, the eagles are under no pressure to move south.

"Perhaps breeding eagles move south earlier than non-breeders or visa-versa. If you are an 'unattached' eagle, you have nothing special to hold you, so you might start wandering away from your summering area sooner, but you also might wander slower and with no particular direction or place in mind. Perhaps age has much to do with it. Maybe older (wiser?) eagles know what they have done for many, many years had suited them well and kept them alive, so they move to these same places on roughly the same schedule each winter. We need to keep thinking and keep learning!

"Challenge Question #3 asked, What good news does the data suggest about the population survey in NY on Jan. 15?

"Did you notice that our population survey took place before #F43 and #F81 returned to New York?! Without satellite tracking, we never would have known. This says two things: 1. We undercount the numbers of wintering eagles using New York, and 2. Our ever-growing wintering population is partially a result of our own success in reestablishing breeders. As our breeding population grows, and as they fledge more and more young each year, those birds are adding to our wintering population. (For those interested in graphing the increase in eagle numbers from 1980 to 2000 see: )

"It is also interesting to note that the National Mid-Winter Bald Eagle Survey is scheduled for 1-15 January each year. This is based upon the idea that eagles have largely arrived at their wintering areas across the country and are static (not moving) by then. Obviously our "new" satellite data is indicating otherwise! However, though we would pick up a few more eagles if the survey date were changed to late January, we would lose consistency of data collection. By doing the survey in the same manner over the same route and time each year, it is thus comparable. And if nothing else, it serves as a useful index to the overall population.

Eagleye Nye
New York State Dept. Environmental Conservation
Delmar, NY

You're the Scientist: Challenge Question #4
Make a "winter range map" for the eagles using the data provide below. (Or print and analyze our map.) Your job is to define each bald eagle's wintering range, and then describe the eagle's behavior within that range. Try to write the best verbal description you can. To get started, look at your map and answer this question:

Challenge Question #4
"What is the greatest distance between two points that each eagle has visited in the past 3 weeks? (Give your answer in miles and kilometers.)"

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

Human Home Range
To put these eagles' travels in perspective, compare them to your own travels. In the past 3 weeks, what is the greatest distance between two places you have visited? Calculate the furthest distance between points within your winter range, then answer this question:

Challenge Question #5
"How does an eagle's winter range compare to your own? What are your reasons for moving? Why do you think an eagle moves around within its home range"

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

Are YOU Ready for the Migration?
Lessons to Hone Your Skills
  • Latitude, Longitude and Distance Traveled
    This lesson will help you get comfortable with satellite data, so you'll have a feeling for the distances involved when latitude and longitude change. (This is especially helpful for those needing practice with decimals.)
  • How to Map Satellite Telemetry Data
    This lesson includes charts with step-by-step instructions for pinpointing latitude and longitude on a map. By putting a transparency on top of your map, an eagle's exact location can be more easily found.

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 #4
(or Challenge Question #5)
3. In the body of EACH message, answer ONE of the questions above.

The Next Bald Eagle Migration Update Will be Posted on March 7, 2000.

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