Eastern Bald Eagle Migration Update:

April 18, 2000

Today's Report Includes:

Latest Migration Map and Data

Field Notes from Biologist Peter Nye
"Incredible! But if you believe the data, Eagle #K70 came back on her winter/capture area last week on the St. Lawrence River--all the way from central Ontario. That's some 500 miles! The satellite fixes were of good quality and appear to be accurate! Why do you think she might have 'dropped back' to the winter site??

Can You Solve the Migration Mystery?

Challenge Question #17
"What do you think happened around April 6 that might have sent Eagle #K70 all the way back to New York as of April 10?" (Clue: Based on their own experiences in the last 12 days, people who live in eastern North America should be able to guess more easily.)

Challenge Question #18
"According to #K70's satellite data from Sunday, April 16, what do you think will happen next?"

"Eagle #K58 seems to keep us guessing as well. First I thought for sure she was going to nest on Prince Edward Island (and we were planning our family vacation up there), then she dropped down to Nova Scotia (which would've been OK too), but now she seems to be back in PEI again! There is still hope!

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:
• From: 42:89:00N 73:59:00W (location on 3/1/00)
• To: 46:90:00N 63:84:00W (location on 3/12/00)
• 541 miles (871 km) between March 1st and 12th

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
Because the eagle diet is primarily fish, biologists pay close attention to the watershed an eagle uses. Any environmental contaminants that enter a watershed might also enter the food chain--and ultimately the eagle! (With a migratory species, ALL the watersheds from which an individual eats during its annual cycle must be considered.) For example, even though Eagle #K72 may nest on a pristine lake or river in Canada this summer, what contaminants might have been in her blood at the time her eggs formed?

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:

 River Mile Nearest Town Predicted Productivity* (# eaglets/occupied breeding territory) 203 Glen Falls 0.99 197 Bakers Falls 0.38 194 Fort Edwards 0.14 159 Waterford 0.64 143 Albany 0.46

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.
Try This!
Make a diagram of the eagle's food chain, using the illustrations and facts on this page: Eagles, Fish and the Food Chain

Challenge Question #19
"Do you think a small, medium or large fish would potentially contain more toxins? Explain why."

Challenge Question #20
"Why do you think loons, who eat small and medium-sized fish, have had fewer problems with environmental contaminants than have eagles, who eat large fish?"

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?"

"I think Journey North is asking this question so that people know how an eagle feels when it is wearing a backpack," said Chris, Bill, Jacob, and Rhyan from New York. "If I wore a backpack, and if I weighed 120 pounds, my backpack would weigh 24 pounds." (pboyle@ogdensburg.neric.org)

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?

Fill a backpack until it weighs 2% of your body weight to see how it feels. As the boys in NY point out, this is what we--and the scientists--are concerned about. Scientists do not want their research to interfere with the life of the eagle. This is for humanitarian reasons, but also because they don't want their research to be affected. The scientists 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.

How to Respond to Today's Challenge Questions