Eastern Bald Eagle Migration Update:
April 18, 2000
Today's Report Includes:
Latest Migration Map and Data
Field Notes from Biologist Peter Nye
(To respond to these questions, please follow
the instructions below.)
Discussion of Challenge Question #12
"This has made it difficult for those of you trying to answer Challenge Question #12. ('How many days did Eagle #K58's migration take? On average, how many miles per day did she travel?') But at the time the question was asked, she had left the wintering area after March 1st, and had reached Prince Edward Island as of March 12th. Using her March 1st and 12th dates and locations, that's 541 miles in 11 days, or an average of 49 miles/day. (It's very important to remember that the satellite readings are not taken every day! Therefore, we must estimate the arrival and departure dates, and the mile/day average is also affected.) Using the format required for the online 'Distance Calculator', Eagle #K58 traveled:
Still Waiting for Eagle #F83's Take Off
"And of course there's Eagle #F83, who left southern NY back in early March, but soon stopped in northern NY in the Adirondacks and has been there ever since. Recall he is the one that went way up into northern Quebec last spring/summer (to 58 N), but wandered around up there, apparently not breeding. Perhaps he's found NY to his liking? Although I'd love to believe that, I doubt it. I'd bet he's just found some eagles up there he is hanging with, and will depart for further north by the end of April. So we'll just have to wait and see..."
Eagle Eye Nye
New York State Dept. Environmental Conservation
Which Watershed? Discussion of Challenge Question #16
"Which watershed do you think Eagle #K70 is now in, the Lake Superior or Hudson Bay watershed? What about Eagle #K72? How can you tell?"
Here is a basic map showing the major river basins of North America. To find the watershed, look at the direction the rivers are flowing in the region where Eagles #K70 and #K72 were on March 28. Notice that the rivers all flow to the north. (In fact, most of the rivers in Canada and Russia flow to the north, and ultimately to the world's largest basin, the Arctic Ocean.)
As Timmy in Plano, Texas noted: "I think that Eagle K70 and K72 are in the Hudson Bay watershed because there is a mountain in between the Hudson Bay and Lake Superior and they are on the Hudson Bay side. So I think that the water on the Hudson side will go downhill to the Hudson Bay by way of the James Bay."
Eagles, Fish and the Food Chain
On average, an eagle's daily food consumption is estimated at 250-550 grams per day, or between 5-10% of its body weight. What contaminants might an eagle be picking up along with the fish? According to one study, environmental contaminants are believed to be the single most important factor affecting reproductive success of eagles. ("Reproductive success" is a measure of how well an animal is able to reproduce.) The higher the concentration of contaminants, the study found, the lower the number of eaglets successfully raised.
Back in New York, Peter Nye has been studying the concentrations of the toxin known as PCBs in bald eagle prey along the Hudson River. By studying prey with known PCB concentrations, he can calculate the PCB concentration likely to accumulate in eagles that consume that prey. And, using results from other PCB studies, he can actually estimate how many young a bald eagle nest can be expected to produce. Nye's study predicted that productivity on the Hudson River would even differ depending on where on river the eagle is feeding. For example:
Bald Eagles typically lay two (2.0) eggs per year. Healthy rates of productivity are considered to be more than one ( >1.0) eaglet per occupied breeding territory.
Make a diagram of the eagle's food chain, using the illustrations and facts on this page: Eagles, Fish and the Food Chain
How Much Do Eagles' Transmitters Weigh?
Discussion of Challenge Question #14
"If you wore a backpack that weighed 2% of your body weight, how heavy would your backpack be?"
Well, luckily for the eagles, their backpacks aren't as heavy as the boys calculated.
Just a small mistake with a decimal would mean a terribly heavy backpack for an eagle! The backpack for a 120 pound
person would weigh only 2.4 pounds. (The 24 pounds the boys calculated would be 20% of the 120 pound person's weight.)
To calculate 2% of that weight, multiply by .02 and you get just 2.4 pounds. (.02 x 120 = 2.4 pounds) Aren't you
relieved to know that eagles don't have to carry a backpack that's 20% of their weight?
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: email@example.com
2. In the Subject Line of your message write: Challenge Question #17
(#18, #19 or #20).
3. In the body of EACH message, answer ONE of the questions above.
The Next Bald Eagle Migration Update Will be Posted on May 2, 2000.