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Monarch Butterfly Migration Update: February 28, 2001

Today's Report Includes:

Field Notes from the Mexican Monarch Sanctuaries

Eligio Garcia Reports Early Monarchs Heading North
The grand exodous from Mexico is still several weeks away, but last week and again this week, Eligio observed a few butterflies flying to the north of the sanctuaries: "Observe dos mariposas cerca de Maravatio pero si creo que ya inicia el regreso al norte," he says. These early sightings may indeed be early migrants, but the masses of monarchs generally depart over about a two-week period in mid-March. By the first week of April, the millions of monarchs will be gone.

Link to this week's observations from the Sierra Chincua sanctuary
Field Notes from Dr. Bill Calvert

February 26, 2001
Greetings from the high altitude tropics--where the weather has turned cold. It sleeted and hailed Sunday night and now the butterflies aren't flying. We only saw two on Monday!
Fortunately, during last week's visits to Chincua and El Rosario, the weather was mostly sunny with a few patchy clouds. When students, parents and teachers of White Bear Lake, MN and I arrived at El Rosario at about 1 pm, the butterflies were flying down to water in droves. Within the area of the clusters, they basked and flew around, among, and over the trees.
The Cloud Effect: Challenge Question #8

Basking butterflies

An occasional small cloud caused a spectacular response from the butterflies known as "the cloud effect." This occurs in the colony when the sun goes behind a cloud. It is especially pronounced after a long morning of sunshine, when the sun has heated the forest and the butterflies are basking, exposed to the sun's rays. Basically what occurs is as follows:

The instant the cloud creates shade, the butterflies that were basking immediately push off into the air. The sound of their wings, which is normally a soft din resembling light rain, increases audibly to a noise like a bee hive. The recently airborne butterflies continue to fly in a fury, until either one of two things occurs:
  1. The sun returns--and the butterflies resume basking in exposed positions as they were before. Or:
  2. The cloud remains--and the butterflies fly back to their clusters, in more protected areas of the forest.

Courtesy of Dr. Lincoln Brower

In this picture, taken from a helicopter by Dr. Lincoln Brower, a cloud has just blocked the sun. Notice the brilliant orange across the treetops, where the butterflies are launching into flight.

The behavior, which is dazzling to witness, is thought to serve an important purpose:

Challenge Question #8
"What purpose do you think is served by the behavior known as the 'cloud effect'. That is, why do you think the butterflies suddenly fly into the air the moment the sun goes behind a cloud?"

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

What's Wrong With This Story?
Challenge Question #9
When at El Rosario, we were told by our guide that about 25% of the overwintering butterflies were not born in the north as the others were. He said these butterflies were the "guides" who presumably led the others back to the Mexican overwintering sites the following year. When asked what food plants these "guides" ate, our guide pointed to a nearby plant. As evidence, he showed us holes in the leaves, and then he showed adult butterflies taking nectar from the flowers of this plant.

Challenge Question #9
"What is wrong with this story? In your answer, explain the term 'complete metamorphosis.'"

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

Until next week,
Bill Calvert (reporting from Valle de Bravo, Mexico)

Mexico's Wet and Dry Seasons
Height of the Dry Season in Sanctuaries

Thirsty butterflies drinking from a seep

Find the Tropic of Cancer on your map (23.5 N). If you live north of this line, you live in the "temperate zone" where temperatures fluctuate greatly with the seasons. Below the Tropic of Cancer (and all the way to the Tropic of Capricorn) is the region known as the "tropics." In the tropics, temperatures don't change very much year round. However, there are distinct dry and rainy seasons in the tropics. It is now the peak of the dry season in the sanctuary region, and water is especially important to monarchs now. Scientists didn't realize this when the sanctuary boundaries were first established. It took many years of observation and study to realize that, during the dry season, the monarchs move to lower elevations within the watershed. They were moving outside of the sanctuary boundaries, to land that was not protected for them.

Dr. Lincoln Brower explains, "One important goal of the newly established sanctuary boundaries was to protect the watershed for the monarchs at this time of year. On sunny days, as winter advances, butterflies fly out of their colonies down-stream for up to 1 km to drink. This enables the butterflies to restore their water balance as the dry season advances. The new sanctuary boundaries take this biological need into account."
Life in the Sanctuary Area
Water Resources for Families
How does life change for people during the rainy and dry seasons? Maria Luisa Mondragon and her family share their stories:

"Imagine carrying 800 liters of water every day to your house from a well a half a mile away ...by foot!" begins Maria Luisa. Luckily you don't have to fill the following with water, but can you fill in the blanks?

Challenge Question #10
"Carrying 800 liters of water is the same as carrying:

  1. ___ bathtubs full of water (assuming one bathtub holds 70 gallons)
  2. ___5-gallon buckets full (like the one Maria Luisa is using)
  3. ___ half-gallon milk cartons full


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

Milkweed Now Emerging on the Migration Trail!

Common Milkweed
Asclepius syriaca

Nature is making ready for the monarchs. During the last week, observers in Texas, Louisiana and Florida report the emergence of native milkweed. On Monday, 7th grade students in San Antonio, Texas reported, "Today on our Signs of Spring Walk we found the first Asclepius asperula on campus. It was 4 cm tall, in excellent condition, and there were no invertebrates found on the plant."

Please report the FIRST MILKWEED to Emerge This Spring!

We hope you will help us monitor the spring emergence of the monarch's food plant across North America.

Today's Map
Winter Monarch Sightings (Pre-Migration)

This map shows where people have reported monarchs this winter:

In order to track the migration accurately, we need to know where monarchs may have remained all winter. People assume the spring migratory monarchs are all coming up from Mexico but we really don't know the importance of the Gulf Coast over-wintering population.

Please Report Your Winter Monarch Sightings NOW!

We need your help before the monarchs arrive from Mexico.

How to Respond to Today's Monarch Challenge Questions:

IMPORTANT: Answer only ONE question in each e-mail message.

1. Address an e-mail message to: jn-challenge-monarch@learner.org
2. In the Subject Line of your message write: Challenge Question #8 ( #9 or #10)
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on March 7, 2001.


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