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Monarch Butterfly Update: March 3, 1998

Today's Report Includes:

Field Reports From the Mexican Over-wintering Sites

To: Journey North
From: Dr. Bill Calvert

February 28, 1998

Principal Monarch Over-wintering Sites in Mexico

Warm dry weather continues to dominate Mexico's Transvolcanic Belt. Mexico City is experiencing minimal pollution with clear, warm days (70's & 80's) and cool nights and mornings (60's).

Farther west in the butterfly overwintering area, the clear, warm weather has stimulated the butterflies to move. Many pour down the mountain during mornings, flooding the town of Angangueo, Michoacan. It is not certain whether these butterflies are the advance party of the return migration, or simply hungry, thirsty butterflies looking for water or nectar. The distance between the Rosario colony (Campanario on map) and the town of Angangueo is at least 3 kilometers, so the trek down to the town represents a considerable energy investment.

It is clear that the butterfly colonies have started to "bud" as they do every year about this time. Butterflies that have made the trek downward do not return to the main colony. Rather, they form "bud" colonies on the mountainside, usually in drainages, below the main colony. These buds can be just below the colony--or halfway down the mountain. At Rosario, there is now a bud colony about 1/3 of the way down the mountain. By mid-March they will be strung out like a string of pearls along the mountainside, all the way to the town.

Clusters in bud colonies are very different in appearance compared to the colonies of mid-winter. They are generally higher up on the branches and are much less densely packed. You can easily distinguish one colony type from the other by these characteristics. Why do colonies "bud" in late winter? Posibilities that are not mutually exclusive include:

1) They go down for water or nectar and conserve energy by not returning to their original elevation.


2) Budding is simply part of the process of colony breakup. These butterflies are headed home!

Mating activity is increasing, especially in the buds. Often 5 or more mating attempts can be seen in a 10 X 10 foot area, though only about 1 in 10 pairs actually join to mate. Mating proceeds like this: A male patrolling the canopy grabs the wings of a female, using the claws on his feet as he encounters her. The pair parachutes down to the ground. She tries to elude being attached to by his claspers. If he manages to attach to her (about 10% of the time), she folds her wings and he then flies off with her, if he can, to a safe perch where mating is completed. He transfers a spermatophore to her. She may use this to fertilize her eggs, or for nutrition. (More on this later.)

In general, butterfly activity during these warm day is intense. Butterflies are flying in the towns and along the paths to the colonies. They flood the llanas (meadows) near the colonies. One gets the impression of a butterfly blizzard.

Dr. Bill Calvert

Reporting from
Angangueo, Michoacan, Mexico

Also visiting the sanctuary region at the same time was naturalist Greg Munson of Rochester, MN. Here's his report:

Responses to Challenge Question #5
To help you prepare to track the migration, we asked this question last week: "Why is it important to note the condition of the butterfly's wings when tracking monarch migration? (That is, whether the wings are fresh or faded and tattered.)"

Students at Corinth Elementry in Shawnee Mission, Kansas said, "We think that you need to look at the monarch's wings when tracking their migrations so you can tell if they were last year's butterflies. You could also see how old they are." (
This is exactly our goal. When you report a monarch this spring, we hope to know whether it is an old butterfly, and has perhaps flown all the way from Mexico, or whether it is a new butterfly, perhaps the young of those now in Mexico. This week's observations of monarchs mating in Mexico reminds us the next generation will soon be on its way.

If you've ever raised a monarch, think back to the bright, fresh color if its wings at the moment it emerged. In contrast,
Evidence of predatation attempt on monarch in Mexican sanctuary.
the butterflies in Mexico have now been alive as many as 7 months. We can expect their wings to show the wear. After all, they've migrated hundreds of miles to Mexico, they've survived winter storms of wind, rain and snow, and the sun has bleached the color from their wings. They may have had some close calls with predators along the way, such as the butterfly pictured here. Before these Mexican monarchs appear at points further north, they will have traveled hundreds of additional miles, and endured additional weathering.

Therefore, when you watch for monarchs carefully note the condition of the butterfly's wings:

Fresh, colorful wings New butterfly
Faded, torn wings Old butterfly

Challenge Question #6
As you continue to wait for the monarch migration to begin, think about this:

Challenge Question #6
"How do you suppose monarchs know when it's time to leave Mexico?" and "What are the consequences of leaving too early or too late?"

How to Respond to Journey North Monarch Challenge Question # 6

1. Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question # 6
3. In the body of the message, give your answer to the questions above.

The Next Monarch Butterfly Migration Update Will be Posted on March 10, 1998.

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