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Monarch Butterfly Update: March 10, 1998

Today's Report Includes:

Field Reports From the Mexican Over-wintering Sites

The monarchs will soon be on their way! Here's the latest news from Mexico, where the butterflies are preparing to begin their trip:

To: Journey North
From: Dr. Bill Calvert

March 6, 1998
Three to 4 weeks of warm, dry, cloudless weather has stirred the over-wintering monarch butterflies up to a frenzy. There is much movement of the colonies down slope. Many millions fly through the woodlands each day to take water and nectar, and perhaps to exercise their wing muscles in preparation for their return migration to the north. One gets the impression of swarming--increased activity in preparation for a move. Much mating is going on in the colonies, every step or so pairs litter the ground.

Sierra Chinchua Sanctuary

Principal Monarch Over-wintering Sites in Mexico

The head of the Chincua colony is now at the bottom of the Arroyo Hondo, in the same drainage or depression down from from Llano del Toro where it was located in mid-January. The colony itself is spread out about 500 meters along the drainage, and it is very narrow, only about 20-30 meters deep. This is a surface area of about 1 hectare. The clusters still very dense. When the butterflies are most densely packed from mid-December to the beginning of February, they number about 13,000,000 per hectare! More on methods of estimating population size next week.

El Rosario Sanctuary
Much the same activities are also occurring at the Rosario site. However, at el Rosario the butterflies are limited as to how far they can descend the mountain, due to cleared agricultural fields beneath the colony. While at Sierra Chincua the butterflies may be as low as 8,500 feet, at Rosario they must remain between 9,000 and 9,500 feet. Nothing is known as to what limits on these agricultural field put on butterfly survival. However, it's very clear that the temperatures are much cooler and moisture levels are much lower at Sierra Chincua than at El Rosario. The agricultural fields beneath the forest clearly increase the heat within the forest. (The overall concern about heat is that it can desiccate the butterflies more quickly.)

Much burning of agricultural fields is now occurring in and around the butterfly over-wintering areas. There are fires everywhere on mountains around the region. Sheep and cow ranchers in the states of Michoacan and Mexico burn in order to return nutrients to pastures. They do this during driest part of the year, believing the nutrients will return to the soil when it finally does rain.

Farmers have probably done this for eons. The effect is to haze up the sky and reduce visibility. What effect if any would you expect this practice to have on the butterflies? One could argue that the haze lowers temperatures because more solar radiation reflected away from the area. Or one could also argue that more heat is retained due to the haze cover. The smoke itself is so diffuse, so unless quite near the butterflies, it probably doesn't have an effect on them. (Lincoln Brower once saw smoke drift into a colony and saw the butterflies move in response.) Fires here aren't as dangerous, as don't seem to crown or get very hot. This is probably because very little dead wood builds up on the forest floor. Until next week,

Bill Calvert
Reporting from
Angangueo, Michoacan, Mexico

South Carolina Teacher Visits Mexican School
Last month, ten teachers accompanied Bill Calvert to the monarch sanctuary region. While there, they visited Escuela Benito Juarez. This school sits beneath the Sierra Chincua sanctuary, and it's the winter home of some of your Symbolic Monarch butterflies. Teacher Marty Siarkowski describes his experience as a highlight of a lifetime. Here is his report:

Letter from Angangueo Student Luis Fernando Romero

Here's news from Fernando--and a chance to practice your Spanish. Special thanks to teacher Jon Dicus of Blake School for help with translation. (We'll provide the English version next week!)

Please report monarchs overwintering and/or breeding in your area.

Last Call: Please Report Over-wintering Monarchs
Before the migration from Mexico begins, we want to know where monarchs have over-wintered this year. During warm years, monarchs can successfully live and breed in the Gulf States. In next week's update, we'll include a map showing all placed monachs have been reported this winter. Report these monarchs as "first" monarchs, but use a winter date for your sighting so we know you are NOT reporting migration.

Reminder: 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 17, 1998.

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