Bald Eagle Migration Update: March 20, 2001 Today's Report Includes: More Eagles Now Moving North! This Week's Migration Map and Data Comparing Migrations: Discussion of Challenge Question #6 Guess Where They'll Nest: Challenge Question #10 Watch the Snow Melt Across North America Male or Female? Discussion of Challenge Question #7 What Does Bortolotti's Formula Say? Challenge Question #11 Eagle Eyes: All the Better to See You With! Discussion of Challenge Questions #8 Discussion of Challenge Question #9: How Do We Know? Vision: An In-Depth Look at Eagle Eyes Challenge Questions #12 and #13 More Eagles Now Moving North! Migration Map This Week's Satellite Data Five of our nine eagles are now on their way! As this week's migration map shows, the first to take off were K70 and E63 (both by March 9th), followed by F43 (March 12th), E47 (March 14th) and E49 (March 16th). We're still waiting for K58, K72 and E50 to move north. Make your own migration map, or print and analyze ours. Because Eagles F43 and F81 were captured in Spring 1998 and 1999 respectively, the batteries in their transmitters are now wearing down. Peter Nye had not been receiving reliable readings so we couldn't be sure whether they'd left the wintering grounds yet or not. This morning, Nye finally received a good reading from F43: "Apparently F43 moved out around March 12th, and as of her March 19th reading, had arrived back on her nesting grounds. How does this departure date compare to her departure dates over last three years? About how long did it take her each year to get back to her nest?", asks Nye. Comparing Migrations Discussion of Challenge Question #6 Last week we asked a similar question, "By what time last spring had each of the eagles begun to migrate?" This chart shows you a summary of last year's migration compared to this year's. What can you conclude about Eagle F43 and the others? Guess Where They'll Nest Every year at this time we challenge you AND Peter Nye to guess where each of his new eagles will nest this spring. Test your wits against the pro! We'll provide Nye's answers along with yours! Challenge Question #10 "Where do you think Eagles E47, E49, E50 and E63 will nest this spring? Give the exact latitude and longitude of their final destination." (To respond to this question, please follow the instructions below.) Watch the Snow Melt Across North America Link to animated NOAA Snow Cover Map As the eagles move north this spring, you can watch their habitat get ready. How does the timing of their migration relate to the melting of ice and snow? This NOAA animated map shows where snow and ice cover is currently found across North America. The animation shows the last 30 days, and it's updated every single day to include yesterday's readings. Amazing! By the way, keep your eye on Eagle K70. Last spring, she had traveled far to the north of Lake Superior by April 4th when a strong, late-season blizzard hit. She turned around and flew 500 miles back to her wintering grounds! Peter Nye was amazed: "Over the years I've had eagles hold-up in a place due to foul weather for up to several days, and even retreat some, but never the distance that K70 moved. She really covered some ground; in only two days, she moved 300 of the 500 miles!" See Last Spring's Migration Map Male or Female? Discussion of Challenge Question #7 In many bird species, it's easy to tell males from females because the plumage is different. Not so with eagles! Challenge Question #7 asked, "What other clues do you think scientists use to determine if an eagle is male or female?" Link to Male or Female? Peter Nye explains, "We can use size measurements from different parts of the eagle's body to determine the sex of the eagles we capture. Female eagles generally have larger wings, feet, talons, beak, etc. A biologist by the name of Bortolotti discovered that the bill and hallux ("toe claw") measurements can be used and their sex can be determined in the following formula: These measurements can be used in the following formula: Sex = (bill depth x 0.392) + (hallux length x 0.340) -27.694 If the answer is positive, the eagle is a female. If the answer is negative, the eagle is a male. What Does Bortolotti's Formula Say? Here are the key measurements from 6 of our eagles. Can you determine the sex of these eagles yourself? Challenge Question #11 "According to Bortolotti's formula, what is the sex of each eagle?" Eagle Bill Depth* Hallux Length* Sex K58 37.9 44.5 ____________ K72 35.9 42.7 ____________ E47 35.0 42.2 ____________ E49 35.5 42.7 ____________ E63 32.6 40.5 ____________ E50 32.4 41.2 ____________ * Bill and hallux measurements are given in millimeters. (To respond to this question, please follow the instructions below.) Eagle Eyes: All the Better to See You With! A typical eagle weighs only about 14 pounds, but eagle eyes are the same size as human eyes! As you can see in this picture of a bird skull, the eyes fill a huge portion of the head. Bird eyes sometimes even weigh more than the bird's entire brain! This pigeon skull shows how large bird eyes really are! Eagle Face Human Face   Last week we asked 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?" This was a hard question--but it has an interesting answer--so read on! An eagle could see the mouse 446 feet away, and can see 2.24 times better than humans can. This is how we figured out the answer: The LENGTH of the mouse is 3 inches. That means we can't think about the AREA of 1 millimeter square, but the LENGTH of it. An eagle has 1000 cones along an edge of that area (the square root of 1,000,000), and a human has 447 (the square root of 200,000). So just considering the fovea, an eagle could see 2.24 times as far as we can see. Congratulations to Grade 7 students at Iselin Middle School in New Jersey and at Hearthside Academy in New York for attempting this CHALLENGING Challenge Question! Both concluded that, since an eagle has five times as many visual cells, it can see five times better. But that isn't quite correct! The important factor is how close those rods and cones are to each other. That's why we need to know how many rods and cones are in a line, not in an area--so it's necessary to take the square root. Here's a picture of a dragon fly, as seen by a human and as probably seen by an eagle. Eagle vs. Human Vision How a distant dragonfly might look to an eagle How the same dragonfly might look to a person Discussion of Challenge Question #9 How Do We Know? Challenge Question #9 asked, "How do you think scientists evaluate how good an eagle's eyes really are? Field observations are one way: If a scientist sees an eagle suddenly plunge down to grab a mouse in a field (sometimes eagles DO eat mice), and can reasonably estimate the height of the eagle when it suddenly made a bee-line for the mouse, s/he would know the eagle could see that distance. Vision: An In-Depth Look at Eagle Eyes Studying the anatomy of the eagle eye and comparing it to a human eye is another way. This is the science of "comparative anatomy." Read this special overview about eagle eyes, then see if you can answer today's Challenge Questions. Link to: Vision: An In-Depth Look at Eagle Eyes Eagles (and other birds) have three eye lids! Their inner eyelid is called a "nicitating membrane." Challenge Question #12 "Why do you think birds have a nictitating membrane?" Challenge Question #13 "Why do humans need oval-shaped eyelid openings to see well? Why do birds need round-shaped ones?" 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 #10 (#11, #12 or #13). 3. In the body of EACH message, answer ONE of the questions above. The Next Bald Eagle Migration Update Will Be Posted on March 27, 2001 Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form