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Monarch Migration Update: October 27, 2000

Today's Report Includes:

Highlights Along the Migration Trail

La llegada: Students in Sanctuary Area Report Monarchs' Arrival
"El domingo varios ninos observaron en lugares distintos de 3 a mas mariposas sobre las flores blancos," reports Escuela Justo Sierra, a school with a view of the El Rosario sanctuary. And from Escuela Emiliano Zapata, "Los ninos vieron estas mariposas en plantos cercanas a sus casas y en el rio."

As this week's data show, the students surrounding the sanctuaries continued to see early-arriving monarchs last week, but not in greater numbers than they reported the week before. Because the migration through Texas came in two distinct waves this year, it will be interesting to see whether this pattern is also seen as monarchs arrive in the sanctuaries. As German Medina Nieto, who drives a truck to the sanctuary for tourists, says: "Ya es tiempo que las mariposas llegan en grupos mas grande." Stay tuned!

Can You Follow the Monarchs' Trail?
Millions upon millions of butterflies are now traveling toward Angangueo, crossing northern Mexico to the sanctuary region. Dr. Bill Calvert describes the migration pathway below.

Here's Dr. Calvert's description of the fall migration pathway:
"At the latitude of the southern tip of Texas, the monarchs' flight path is only about 8% as wide as it was when they started from their breeding grounds in the North. This funneling is due to the Gulf of Mexico and Mexico's Sierra Madre Oriental (the Rocky Mountain's extension into Mexico). Enormous numbers of monarchs travel through the mountainous areas in the Mexican states of Coahuila and Nuevo Leon and further south, because these geographic features compress the monarchs' flight-path. When they reach deep, central Mexico they get thicker and thicker and are easier to find as they are concentrated by the Sierra Madre Oriental along which they fly.

"These mountains seem to focus the migration, and direct it towards the overwintering sites located in the Transvolcanic Belt of central Mexico (19 N, -100 W). The Sierra Madre Oriental forms a great elongated massif that stands in the path of the easterly winds that predominate at this time of year. In short, as easterly winds blow, the butterflies get a 'lift' from these winds. The air rises over the east-facing mountain slopes of the multiple ranges of the Sierra Madre Oriental. When the butterflies fly through the inner montane valleys of the Sierra Madres, this rising air makes flight much easier. During late afternoon, after a day when no or few butterflies have been seen, they often quite suddenly 'fall out' of the sky and begin to nectar or to form their evening roosts.

As you read his remarks:

  • Look at a physical map of Mexico and see if you can find: The Sierra Madre Oriental mountain range, the Sierra Gorda Mountains, the Transvolcanic Mountains, and the Nevado de Toluca volcano.
  • Look at a political map of Mexico and see if you can find these towns: Ciudad Acuna, Monclava, Santa Catarina, Linares, Galeana, Ciudad Victoria, Jaumave, Ciudad del Maiz, Cardenas, Rio Verde, Jalpan, Queretaro, Tesquisquiapan, Coroneo, Contepec, Mil Cumbres (curve in road between Ciudad Hidalgo and Morelia), Angangueo.

Tip: The National Geographic Atlas of the World shows most of these towns.
Now try this question:

Challenge Question #15
"What is the name of the Mexican state each of the above towns is in?"

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

Finding the Narrow Finishing Line

Dr. Calvert watching as
monarchs arrive in Mexico's sanctuary region.

"Amazingly, the sanctuary area the monarchs target is very, very narrow. The western-most side is at 'Mil Cumbres' (-100.8 W, a large wiggle in the road between Ciudad Hidalgo and Morelia) and the eastern-most side is the Nevado de Toluca (-99.7 W). This is an area only is 1.1 degrees wide, in longitude. This means that, assuming that monarchs cannot 'home' and correct the consequences of a miss, those migrants flying in from the north must strike the Transvolcanic Belt somewhere within this 1.1 degree window to find the overwintering sites!"

Challenge Question #16
"Based on the measurements Dr. Calvert provides, how wide is the monarchs' finish line? Name a town that is the same distance from your town, so you can visualize this distance."

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

This winter, the entire eastern population of monarch butterflies in Mexico will cluster together on only 10-12 volcanic mountains, in large colonies estimated to contain millions of individuals. Significantly, an estimated 80% of the butterflies concentrate each year in only four core colonies. (All of the colonies are in Mexico's Transvolcanic Belt, and most of these colonies are spread along an arc from the western face of the volcano "Nevado de Toluca" to the northeastern extreme of the state of Michoacan. The four core sites are located in the center of the arc, near Angangueo.)

Going, Going, Gone?
As the migration from Canada and the U.S. draws to a close this fall, we hope you are watching for your LAST monarch of the year. How late in the season do you think monarchs will be found in your region?

Please Report Your LAST Monarch of the Season
Please keep watching for butterflies in your area, and report the FINAL monarch you see this fall. We're still receiving reports from the frosty north so as you can see, you need to wait a looooong time to be sure you've seen your LAST monarch:

10/20/00 Pittsburgh, PA (40.47 N, -79.95 W)
"After last week's cool weather, we weren't sure whether we'd see any more monarchs, but today we saw two more!" Ms. Rava's First Grade at Ross Elementary (

10/20/00 Toronto, ON (43.72 N, -79.41 W)
"Although we had a heavy frost on the October 6th weekend, it seems that some monarchs have survived that event. Since last Wednesday, October 18th to Sunday , October 22, the weather has been extremely warm in south western Ontario. Monarchs were sighted at the local schools near Brantford and Tillsonburg at different times during the warm spell. I saw 2 on Saturday and 2 on Sunday. They are certainly welcoming any New England Aster or Butterfly bush with flowers for a quick meal. Then they are off again , heading south probably for Long Point or Point Pelee. What a treat for the end of October!" Mr. Chipps Grade 10, Sir John A. Macdonald Collegiate Institute (

Not All Monarchs Go to Mexico
Residents of the Gulf States and California: Please help us document whether monarchs remain in your region throughout the winter. Plan to record all your fall and winter sightings. When we begin to track migration next spring, we hope you'll report whether monarchs were present all winter. (Watch for instructions when Journey North begins next February.)

FINAL Fall Monarch Migration Updates: Fridays, Nov. 3rd and 10th
Now that the monarchs have begun to arrive in the sanctuary region, we expect to have just two more updates for the fall season.

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 #15 (or #16)
3. In the body of the message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on November 3, 2000.

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