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Monarch Butterfly Migration Update: February 27, 2004

Today's Report Includes:

Field Notes from Mexico by Dr. Bill Calvert
Dr. Calvert phoned home from Mexico on Wednesday after visiting the Sierra Chincua sanctuary. The season is progressing right on schedule. "The most intense part of the dry season is beginning now," he said. "The forest is literally drying out. And the butterflies no longer can take water from dew patches, or wet areas in the forest, because they’re drying up."
Monarchs form tight clusters during cold temperatures. On sunny days, they fly away from the colonies. As the dry season advances, the tight colonies break up. The butterflies go to lower elevations where there is water and don't return.

Writing Prompts for Your Science Journal
  • What is an arroyo?
  • Why are arroyos so important to monarchs at this time of year?
  • How did the January frost hurt monarch habitat now, in late February?

Seasons in the Tropics: Wet and Dry

What causes the wet and dry seasons in the tropics? See National Weather Service

Find the Tropic of Cancer on a globe (23.5 N). If you live north of this line, you live in the "temperate zone." In general, temperatures fluctuate greatly with the seasons in the temperate zone. So does the amount of day light (photoperiod).

Below the Tropic of Cancer--and all the way to the Tropic of Capricorn (23.5 S)--is the region known as the "tropics." In the tropics, temperatures and photoperiod don't vary much year round. However, precipitation does vary greatly.

There are distinct dry and rainy seasons in the tropics. The cycle of the seasons in the sanctuary region of Mexico follows this pattern:

  • Dry Season: November to May
  • Rainy Season: May to October

Scientists Learn from Butterflies: More Land is Needed
When land was put aside to protect the monarchs in 1986, the biological needs of the over-wintering butterflies were not well understood. It took many years of study to realize that, during the dry season, the monarchs move to lower elevations where there is water. Over time, scientists realized that the monarchs were moving beyond the sanctuary boundaries. The land the butterflies needed during the dry season was not protected for them.

Dr. Lincoln Brower explains, "One important goal of the newly established sanctuary boundaries (November, 2000) 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."

Tropical vs. Temperate Zones: Watch the Seasons Change
Watch how the seasons change in different parts of the globe. Try this simple activity once a month from March to June. Predict the temperature and day length at your temperate zone home and at the monarch’s tropical winter refuge. Then check your predictions against the actual data.

Life in the Sanctuary Area: Water Resources for Families
How does life change for people during the rainy and dry seasons? Maria Luisa and her family share their story.
water16 water21

Imagine carrying 800 liters of water every day to your house from a well a half a mile foot!" begins Maria Luisa.

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

Discussion of Challenge Question #4
Bough-full of Butterflies

"If the typical monarch weighs 500 mg in midwinter, how much would a branch loaded with 15,000 butterflies weigh?," we asked.

"There are about 16.5 pounds of butterflies on one branch," say Grade 3 students at Ferrisburgh Central School, Ferrisburgh, VT.

What else did they find that weighs the same? Two newborn babies, or 128 Star War Action figures, or 4 ibooks, or 3 bags of flour or a partly filled box of computer paper, say the students! Here's their math.

How Many Paper Clips Bend a Branch? Just Ask Nikki!

Mrs. McGehee's students in Illinois

Thursday at recess Mrs. McGehee's students tried the paper clip test suggested in the Feb. 20 update. They have been studying measurement in class and knew that a paper clip weighed approximately 1 gram. They estimated that the branch would bend at between 250 - 500 paper clips.

“At 310 paper clips the branch, which we considered a medium size branch, began to bend. Nikki was the closest estimate at 320 paper clips,” they said.

Great job! So, if the typical monarch weighs 500 mg, how many monarchs could bend the same branch?

Did You Know? 
The monarch's behavior of moving during the over-wintering season is an example of an adaptation.
Discussion of Challenge Question #5
Reasons Monarchs Move

“Monarchs move during wintering because they need to survive,” said Mallika of Harrington School in Lexington, MA. “They might move because of hail, rain, predators, climate changes, and more. Also because they need a certain amount of warmth and moisture,” she added.

Milkweed Emerging on the Migration Trail!
On the Texas mid-coast, Harlen Aschen reports the first native milkweeds appearing in the garden. Based on past experience, he predicts that the two main native milkweeds for monarchs in the area should also be sprouting over the next two weeks. Hooray! Please help monitor the emergence of the monarch's food plant across North America.

Report the FIRST MILKWEED LEAVES to Emerge This Spring!

Please Report Winter Monarch Sightings NOW
This map shows where people have reported monarchs this winter:

Challenge Question #7:
"Do you think the monarchs that are now spread along the Gulf Coast, from Texas to Florida, will migrate north this spring? Or will all the butterflies come from Mexico? How might we be able to tell?"

How to Respond to Today's Challenge Questions:

IMPORTANT: 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 #6 (or #7)
3. In the body of EACH message, give your answer to ONE of the questions above.

The Next Monarch Butterfly Migration Update Will Be Posted on March 5, 2004

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