Monarch Butterfly Monarch Butterfly
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Monarch Migration Update: March 11, 2005

Today's Report Includes:

Field Notes from Mexico from Dr. Bill Calvert
"Never was the importance of shelter illustrated so dramatically than it was at the Chincua sanctuary yesterday," began Dr. Calvert in a phone conversation on Thursday. "High altitude, westerly winds were blowing dry, cool air at nearly gale force. Trees were blown, branches shook, butterflies lost their grip and were strew about the ground."

What happened to the monarchs that did not move out of the wind? Can you find at least three dangers they encountered?
A Late Migration?
"I don't think any of them had left yet," continued Calvert. "It's very wet and colder than usual. My impression is that heat is a factor in driving them. It will be interesting to see if you get delayed reports because of all the cold weather."

Food, Water, Shelter, and Space: Today's Focus is FOOD

Look at this graph before reading further. What does this suggest about food in the monarch's winter habitat? If your weight changed this much between November and April, how much would you weigh today?

Survival of the Fattest
It's now mid-March. How much fat does the typical monarch have left by now? If weight-loss were to continue at the same rate, when would most monarchs run out of fuel? Running out of fat is a common cause of death. "Monarchs that you see littering the ground have usually starved to death," says Dr. Calvert.

The Monarch Food Budget: Spending What They Earned
Journaling Question
Why does a monarch butterfly burn less energy when temperatures are cool? Explain your reasoning.

Here is a unique feature of the monarch's winter habitat: Rather than provide food for millions upon millions of butterflies for five months, its cool temperatures allow monarchs to SAVE energy.

Where did they get the fat they are burning?

  • In the north as caterpillars
  • In the north during fall migration

Is Nectar Important?
It's common to see butterflies drinking from flowers in the over-wintering area. One might quickly conclude that YES, nectar is important. A study by Dr. Lincoln Brower and Eduardo Rendon disagrees: Monarchs that are visiting flowers are starving to death, they believe. Those butterflies are "running out of gas." They resort to nectar in a futile attempt to stay alive. In contrast, the monarchs clustered in the trees are healthy and don’t need nectar. They still have enough stored lipids. Here’s information and data from their research:
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Photos Courtesy of Dr. Lincoln Brower, Sweet Briar College

Scientists Don’t Always Agree
"As far as I'm concerned, this question is unresolved at this time," says Dr. Calvert. "This suggests that butterflies are wasting their time nectaring, and I have a little trouble with the notion of creatures wasting their time in nature."

He agrees that there are too many butterflies for local plants to supply sufficient nectar. "However," he says, "we don't know much about what they do if they survive until, say, the beginning of March. It may be that the ones that are starving are just driven out of the colony and they find nectar on the routes to the north. That's a real possibility. We haven't really measured. We haven't looked at butterflies to the north of the overwintering areas. Indeed they are almost impossible to catch and measure."

Challenge Question #6: What Food Will Monarchs Need Soon?
The migration is about to begin. Consider this:

Challenge Question #6
"Aside from nectar, what food are monarchs about to need in great supply? Explain how you think food might be related to the timing of monarch migration."

Discussion of Challenge Question #5:
How Are These Monarchs Avoiding Predators?

Mrs. Anderson's Grade 6th grade class in Plymouth, MN inspected last week's photos carefully. They did a splendid job considering how the forest protects monarchs from predators. Here's what they said:
  • We think it helps them by making it harder to catch them when they are
    up in the trees. The mice can't get them as easily.
  • Also, it is like a school of fish. It is harder to focus on one monarch and catch that one because of the others.
  • They also camouflage in the trees. They look like leaves.
  • The trees keep the monarchs drier and warmer. The monarchs are warmer
    when they cluster. Then they won't fall to the forest floor from the
    cold. Predators can get them more easily on the floor.
Dr. Lincoln Brower, Sweet Briar College 
 Monarchs climb any plant they can find to stay off the forest floor. Notice how well monarch wings match the oyamel forest. >> Safety in numbers:
Too many for one to eat

The Stage is Set for the Migration: Are You Ready?
"The milkweed is here, so the stage is set. We're waiting in the audience for the actors to come on stage. The play should begin in the next few days," wrote Carol Cullar poetically from Eagle Pass, Texas. Based on observations in past years, monarchs should arrive there within the next 7-10 days, she predicted on March 8.

Predicting the Route of the Monarch's Spring Migration
As the monarchs pour out of Mexico this spring, where do you think they will arrive first? What pathway do you suppose they will travel? Follow this key lesson as you track the migration during the next three months.

Ask the Expert Open Through March 18
Once again this year, monarch biologist Dr. Karen Oberhauser has volunteered to respond to students' questions. We are thrilled to offer this opportunity to you!

How to Respond to Today's Monarch Challenge Question

1. Address an e-mail message to:

2. In the Subject Line of your message write: Challenge Question #6

3. In the body of your message, answer the question above.

The Next Monarch Migration Update Will Be Posted on March 18, 2005

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