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Monarch Migration Update: September 13, 2000

Today's Report Includes:

Highlights Along the Migration Trail

Strong Cold Front Pushes Monarchs Through Iowa
Writing from Des Moines, IA, where a cold front arrived late Monday afternoon, Dr. Bob Woodward describes conditions that were "superb for watching a monarch 'event'." Here are his comments, along with those from others who witnessed the strong migration Monday in Iowa:

"A spectacle of nature occurred late Monday afternoon in the skies over central Iowa. The day's temperature had tied a record high at 97, and a cold front was passing through from the northwest to southeast. At approximately 4:30 p.m., migrating monarch butterflies could be seen in the sky floating on the wind, their shadows showing sharply against the clouds above. As the wind picked up in intensity, monarchs could be seen flying high and quickly, floating speedily on the wind, or being pushed to the east by the windy conditions.

Cold front moving through Iowa. (Click to view larger map.)
Above our butterfly garden in Altoona, Iowa, approximately 100 monarchs were counted in about 40 minutes from 5:20 p.m. to 6 p.m. as the cold front passed through the area. Many of the monarchs could be seen only through binoculars while others could be seen with the naked eye as their shadows showed on the clouds above. It was a riveting event and displayed the extremes of weather through which the monarchs must pass as they make their way southward to Mexico." Drake University (
See Dr.Woodward's website "Save the Monarch", with journal of daily observations.

09/11/00 Waterloo, IA (42.29 N, -92.20 W)
"There were clouds of monarchs in the air as the front moved through Waterloo, Iowa on Sept. 11. They were thick in the air above the cars. A teacher at my building said what appeared to be over 100 monarchs roosted in her neighbor's tree last night. We did not get any rain out of this front, but the temperature dropped significantly." Kittrell Elementary (

09/11/00 Tama, IA (41.58 N, -92.34 W)
"We saw a large number of monarchs right after the storm last night. The front passed here around 7 pm. With it, the wind changed around from the north and temps cooled by at least 10 degrees. At that time, monarchs were everywhere among the trees. There were hundreds of monarchs in our yard at that time. They must have continued on with the front because they were not roosting in the trees this morning. We are located in east central Iowa along the Iowa river." (

9/12/00 Cedar Rapids, IA (42.00 N, -91.38 W)
"Wow, here they come right on schedule. Knowing that I spotted them last year between the 12th and 14th, yesterday I searched and searched and only spotted one. It was very hot in the 90's. Today, however, amazingly again on Sept. 12th, I spotted 79 within a half hour of driving (approximately 6 miles). Last night a storm brought clear skies and cooler temperatures in the 70's for today." (

Will the Same Cold Front Trigger Migration in the East?
Cold fronts are shown as blue lines on a weather map. Click on image to watch the Sept. 12 & 13 cold front move.
Visit the
CNN website for daily weather forecasts (QuickTime).

By this evening, September 13, the same cold front that pushed through Iowa on Monday will have moved across the continent. Observers throughout the eastern U.S. States and Canadian Provinces are anxiously waiting for the migration to begin there in earnest. Observers report very few monarchs at all--and only weak indications of migration.

We asked Dr. Lincoln Brower for his thoughts about this apparently low numbers of monarchs. He replied: "It is a mystery to me....There have been virtually no migrants here in Virginia at all to date. However, we have not yet had a strong cold front push through. If we do not start seeing migrating monarchs by the end of this week, then we can begin really wondering."

Cold Fronts, Wind and Fall Monarch Migration
How is the flight behavior of monarchs affected by cold fronts? Generally, says Dr. Calvert, when winds are from the south, monarchs are flying low, and are the most visible to observers. When the winds shift to the north, monarchs move to high altitudes where the winds are stronger--but where the monarchs are less visible to observers.

"It's easy to see why monarchs come in on cold fronts," says Calvert. "It's like catching a bus going your way - in this case the ride is even free! Monarchs probably ride the layer of uplifted air associated with the advancing edge of these cold fronts. But that is not all they ride. They generally move with any wind that has a northerly component and may still be seen traveling days after the front has past. They may also migrate in not-so-strong southerly winds! In these cases, they are often found flying low to the ground and are very noticeable."

Peak Migration Now in Nebraska
The southernmost edge of the peak migration now appears to be in Nebraska, according to observers there. A flurry of reports arrived from that state beginning last Wednesday. Read these observers' comments, note the date of their sightings, and then check the Weather Map Archives to investigate how weather conditions affected the migration:

When Will Monarchs Reach the Sanctuaries? Revisiting Challenge Question #2
As you watch the migration move down your map, revisit your prediction--and let us know what you think!

Challenge Question #2
"When do you predict the first monarchs will be sighted in the sanctuary region this fall? (Or, as the tired travelers might ask, "When are we going to be there?" )

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

Four Ways to Watch for Migrating Monarchs
The four observation methods described below include many helpful tips for making your fall migration-watching interesting and valuable. Included are descriptions from experts, and links to websites with examples.
  • Method #1: Stationary Count
  • Method #2: Road Census
  • Method #3: Count of Monarchs at Overnight Roost
  • Method #4: Count of Monarchs at Nectar Source

See: "Four Ways to Watch for Migrating Monarchs"

How Many Monarchs in the Alfalfa Field?
Challenge Question #3

The monarchs now passing through the Midwestern states are moving through the U.S. "Corn Belt," so named because so much of the land is planted in corn. In fact, where there was once prairie, as much as 90% of the land is now planted with crops. Monarchs looking for nectar in this region sometimes find alfalfa fields in bloom--a good source of nectar.

Surrounded by miles of corn and soybean fields, the 40 acres of blooming alfalfa shown in these photos is a magnet for hungry butterflies. Alfalfa hay is used for milk cows, and farmers rarely allow alfalfa to bloom because the food value of the hay decreases when it's allowed to flower. On this fall day, the alfalfa was in full bloom and there was a butterfly every 8 feet--so many butterflies that the field itself appeared to be fluttering.

Challenge Question #3
"How many monarchs do you estimate were nectaring in this single 40 acre alfalfa field?"

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

When Will the Migration Reach You?
Discussion of Challenge Question #1

Fall 1999 Migration
(Click on map to enlarge.)
Challenge Question #1 asked, "According to the Journey South migration map for Fall 1999, between which dates did the Monarch Migration peak in Ontario, Massachusetts, Oklahoma and Texas last fall?"

Students in Ms. Dempsey's Second Grade Class in Framingham, MA, and in Mrs. Kloewer's 4th Period Science Class in York, NE agreed:
  • Ontario: September 15-24
  • Massachusetts: September 22-28
  • Oklahoma: September 29-October 5
  • Texas: October 6-12

"We think that's moving pretty fast for some little creatures," said the Nebraska students.

Reminder: EARLY Symbolic Migration Deadline--October 2nd
Only 19 more butterfly-making days before the deadline. Don't be late! Butterflies received after the postmarked deadline cannot migrate!

How to Respond to Today's Monarch Challenge Questions:

IMPORTANT: Please answer ONLY ONE question in each e-mail message!

1. Address an e-mail message to:
2. In the Subject Line of each message write: Challenge Question #2 (or #3)
3. In the body of the message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on
September 20, 2000.

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