Monarch Butterfly Migration Update: September 17, 2004
Today’s Update Includes
Highlights From the Migration Trail
We have tracked the fall migration to Mexico for eight years. For the first time, we can't determine the migration's leading edge or any peak. Reports of monarchs are coming in--100 sightings during the past week--but they are scattered all over the map. Also noteworthy are observations of eggs and larvae in northern regions, perhaps suggesting late reproduction. Comments about LOW NUMBERS, such as the following, are being reported regularly:
Interactive Maps: Read All Reports on the "MapServer"
All monarch sightings that have been reported are displayed on our MapServer. You can “click” to read each observer’s comments.
Journey North Archives: Fall 1997-2003
Visit our archives and read for examples of how this year's migration is different than those in past years:
This Week's Fall Migration Focus: Flight
During the past two weeks, we have written about monarchs resting in roosts and fueling their flight with nectar from flowers. But migration is about traveling. So let's take a look at monarch flight this week...
Wind and Thermals: Two Ways Butterflies Fly Free
On windy days, monarchs can catch a free ride. If the wind is from the north, they can glide effortlessly southward. (Which weighs more, an autumn leaf or a monarch butterfly?)
On sunny days, monarchs can rise into the sky on “thermals.” (A thermal is a column of rising air. Thermals occur in places where the sun heats the earth unevenly.) When a monarch is lifted by a thermal, it circles in tight spirals, and goes higher and higher. Then it glides downward and southward to catch the next thermal.
Free Ride to Mexico: Glide Don't Flap
When a monarch glides or rides with the wind, it burns no more energy than when it is sitting still. (The rate of energy burned while at rest is called the "resting metabolism.") Gliding provides a free ride. It's as easy as riding a bike downhill. In contrast, "flapping" or "powered" flight takes a lot of energy.
Dr. David Gibo is a glider pilot. (A glider is an airplane without an engine.) He is also a scientist who is interested in studying monarchs. So, Dr. Gibo has thought a lot about monarchs, gliding and energy use during flight.
According to calculations by Dr. David Gibo, who’s a glider pilot himself, a monarch burns 140 mg of fat to either:
How Expensive is Flapping Flight?
Flapping Flight: A Look at Flight in Slow Motion
Here is a video clip of monarch flight in slow motion. The action is slowed down 50 times. This means the video clip lasts fifty times longer than it did in reality. In other words, we recorded this monarch flying for one half second and then stretched it out to last for 25 seconds.
During “powered” or “flapping” flight, monarchs flap their wings about 5 to 12 times a second, depending on how hard they’re trying to move. They flap at the slower rate when flying leisurely, such as during migration. The faster rate is needed when flying into a strong headwind, or when trying to escape from a predator, for example.
Video Clips and the Scientific Process
Observation is the first step in the scientific process. Video clips provide an opportunity for students to make authentic scientific observations. Here are some suggestions for viewing video clips as a scientist:
Field Trip in the Sky: Flying in a Thermal
By Elizabeth Howard
I had read about thermals, but now I understand them. Thanks to Dr. Ian Worley, pilot and professor at the University of Vermont, I went up into the sky and found out what it's like to fly in a thermal.
We hopped aboard his plane and headed for the sky. But where would we find a thermal? And, I wondered nervously, what WOULD it feel like to fly through one in a small plane?
Reminder: Symbolic Migration Deadline Oct 15
Only 42 more butterfly-making days before the Symbolic Migration deadline. Don't be late! Butterflies received after the postmarked deadline cannot migrate.
How to Respond to Today's Challenge Question
1. Address an e-mail message to: firstname.lastname@example.org
2. In the Subject Line of the message write: Challenge Question #5 (or #6)
3. In the body of the message, answer the question above.
The Next Monarch Migration Update Will Be Posted on September 24, 2004.
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