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Monarch Migration Update: February 23, 1999

Today's Report Includes:

First Weather Report from Pedro Ascencio School

To enlarge, click on face of map.

Students at this small country school live beside the largest monarch sanctuary in the world, the Sierra Chincua. Monarchs often fly silently over the schoolyard, to and from the sanctuary. Find their community, "Garatachea", beside the sanctuary on this map.

At 10,000 feet elevation, where the monarchs spend the winter, over-night temperatures can drop to freezing. All of Mexico is not warm and sunny! As Dr. Calvert explained last week, cold temperatures, wind, rain--and even snow--can affect the entire population of monarchs resting in this region. With the new weather station, Pedro Ascencio students will monitor the local climate. This will help us understand how the climate and weather change during the over-wintering season. Here are their first week's observations:

15 febrero - 20 febrero


Temperatura Maxima



Helada o Rocio?

Lunes, 15 febrero





Martes, 16 febrero





Miercoles, 17 febrero





Jueves, 18 febrero





Viernes, 19 febrero





Sabado, 20 febrero





Challenge Question #5
"According to Pedro Ascencio students, which day was the warmest last week--and which night was the coldest? (In your answer, convert from degrees Celsius to Fahrenheit.) In addition to temperature and photoperiod, what else are the students measuring? Any ideas why?"

Over the weeks leading up to the monarchs' departure, we'll send this data in each report. Predict how temperature and photoperiod will change between now and time the monarchs leave in March. A graph like the one shown will help you see these changes. (To enlarge, click on face of graph.)

Coming Next Week
Symbolic Monarch Migration Update

Gustavo de Jesus Castillas with butterfly sent from Sarah in
Delaware, NJ

Whose butterflies landed at Pedro Ascencio school? Next week we'll introduce you to each of the students, and show you whose butterflies they are caring for. We'll take you home with the students see how children in this region live.

Field Notes from Mexico
by Dr. Bill Calvert
Teachers traveling with Dr. Calvert visited Pedro Ascencio last week, and were greeted by Profesor Gilberto Salazar Vargas. "Por lo cual los ninos estan muy contentos, " he said. "Para mi es un grato honor mandarles esta informacion y lo seguiremos haciendo con gusto." We hope to have personal notes from the U. S. teachers in a future update. In the meantime, here's the news from Dr. Calvert:

February 22, 1999
After last week's cold snap, warm temperatures have returned to the butterfly areas. The major effect of last week's cold weather appears only to have been to hold the butterflies in place on the slopes of the mountainside. There was no noticeable increase in mortality. There has been no apparent movement downward since my first observation of their position on Feb 8. Also, the clusters are still densely packed on the oyamel trees as they are in mid-season. (See Eligio Serrano Garcia's records below.)

But this is about to change. As the ambient temperature heats up the butterflies will leave the colonies and not return to the dense cluster. Instead they will move downslope and re-form in smaller clusters, higher in the canopy, and more widely dispersed in the forest. The colony will cover a wider area and will appear less densely packed. This dispersion from dense packing later in the season suggests that the close-packing does serve to warm them during the cold part of the season. (See Eligio's note below.)

Until next week,
Bill Calvert

Monarchs' Use of the Sierra Chincua Sanctuary
Biologist Eligio Serrano Garcia has been measuring the surface area and number of trees covered with butterflies at the Sierra Chincua Sanctuary each week for Journey North. Let's watch how this changes as temperatures warm, and the butterflies move as Dr. Calvert predicts they will:

Surface Area and Trees Covered with Butterflies at Sierra Chincua



# Trees













How Many Monarchs Are in Mexico?
Discussion of Challenge Question #3
Mrs. Cheney's students in Sugar Grove, IL, and Ms. Matusumoto's class in Minneaplis, MN agree: According to their estimates this year's monarch population stands at 56,030,000 butterflies! Translating hectares into butterflies, here are the past years' records:
How Many Monarchs Were in Mexico?


# Hectares

of Monarchs










Lowest in past 5 years



Estimates Based on Estimates
In order to protect monarchs, scientists need to know if their population getting smaller, larger or staying the same. As you've seen, these population estimates are made by combining two estimates--and there's lots of room for error! First you used the scientist's estimate of the number of hectares the butterflies cover. Then they you multiplied that number by 13,000,000-- the estimated number of monarchs per hectare. Dr. Calvert made this estimate using a method called " Mark, Release, Recapture".

Try This!
  • Try a "Mark, Release and Recapture" estimate in your class (advanced students):
    Link to Mark, Release and Recapture Lesson
  • Compare the area covered with butterflies at Sierra Chincua on February 4 and on February 11. If you were a scientist visiting the sanctuary to estimate the population size, how much would your estimate vary depending on the day you visited?

How Many is 56 Million?
It's hard to imagine such a large number! Let's translate butterflies into people and see what we get:

Challenge Question # 6
"Begin with the population of your state or province, then start adding! Add the population of as many neighboring states or provinces as you can, until you reach 56 million. If you gave 1 butterfly to each person, people from how many neighboring states/provinces would get a butterfly?"

Don't Anybody Sneeze!
Think how a cold can travel through your family, your class-or even your entire school! Disease is one obvious risk of having all the butterflies crowded into one place for the winter. But that's not the only challenge the butterflies face:

Challenge Question # 7
With the entire population of monarchs gathered in one place, how many risks to the butterflies can you think of? Are there any benefits?

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 your message write: Challenge Question # 5 (or Challenge Question # 6)
3. In the body of EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on March 2, 1999.

Copyright 1999 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form

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