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Monarch Migration Update: February 16, 1999

Today's Report Includes:

Mexican Monarchs on National Public Radio Next Monday
Tune in next Monday morning, February 22, for a National Geographic "Radio Expedition" to the monarch sanctuaries in Mexico. The program will include an interview with monarch biologist Dr. Lincoln Brower during a recent trip to the Sierra Chincua and Rosario overwintering sites. It is scheduled to be broadcast on NPR's Morning Edition (7-9 am), and after airing will be archived on the WWW at:

Field Notes from Mexico by Dr. Bill Calvert
A strong, cold air mass from the north (called a "norther" ) has blown deep into Mexico, bringing unseasonably cool temperatures. It's downright COLD for this part of the world!

We haven't been to the sanctuaries since cold weather hit on Thursday, so we have yet to see the effect of this storm system. But past experiences indicate that cold weather--accompanied by snow, sleet, hail and high winds--is bad news for butterflies.

Last week, when warm and dry, butterflies at the El Roario and Sierra Chincua sanctuaries were extremely active, traveling as much as 1 km out from the colonies to drink water and take nectar. Butterflies numbering in the thousands, and in some cases tens of thousands, were a common sight at seeps and wet spots where streams cross roads.

A new entrepreneurial venture was launched at the El Rosario sanctuary: For 1 peso (10 cents), visitors may leave the main trail and go into an area where spring water soaks the grassy ground. (Some of the water has been diverted into a channel.) Drinking butterflies accumulate there by the thousands, and benches are provided so people can relax and mediate.

How Many Monarchs are in Mexico?
Last week, we asked you to imagine counting all the butterflies in Mexico. Meet Eligio Garcia Serrano who's job it is! Eligio works for the Mexican government's National Institute of Ecology (Intituto Nacional de Ecologia, "INE") and is graciously forwarding news to Journey North this spring. Now how do you suppose these scientists go about estimating the monarch population size?

In last week's update, Bill Calvert gave a clue about WHEN it's best to count butterflies: He said the monarchs cluster tightly together during the coldest months. This is exactly when biologists make their estimates. They travel to all the monarch sites and measure the total surface area that all the clusters of butterflies cover.

Here's another clue from Dr. Calvert: "In 1986, we did a 'mark & recapture' study at one of the sites in January. On the basis of that study we estimated 13,000,000 monarch per hectare. Albeit crude, you can use that figure to estimate the size of the total monarch population for a year."

According to Eligio's measurements, in total this year the monarchs cover less than 6 hectares. Significantly, almost 4/5 of the population is found in only 2 sanctuaries. Here are his measurements for the winter of 1998/1999:

Sanctuary Surface Area Covered With Monarchs*
El Rosario

2.00 hectares

Sierra Chincua

1.96 hectares

All 3 other sanctuaries

1.25 hectares

*These measurements include only the 5 sites located in the Reserva Especial de la Biosfera Mariposa Monarca (REBMM), the sanctuaries which are protected by the Mexican government: Altamirano, Sierra Chincua, El Rosario, Chivati, and El Pelon.

Since monitoring began, the lowest coverage recorded was 3.5 hectares. Here are the records from the past several years. (Get ready: You'll need a little Spanish to do today's Challenge Question!)

  • En la temporada 1997-1998 las colonias de mariposas dentro de los cinco santuarios ocuparon 4.53 hectareas.
  • En la temporada 1998-1999 las colonias de mariposas dentro de los cinco santuarios ocuparon 4.31 hectareas.
  • La temporada que mayor numero de hectareas ocupo la mariposa desde hace 5 años fue en la temporada 1996-1997 que ocupo 17.63 hectareas.

Challenge Question # 3
"According to Eligio Garcia's statistics, how many monarchs do you estimate were in Mexico during the winters of: 1998/1999, 1997/1998, 1996/1997? What are the fewest and greatest numbers of butterflies estimated in the last 5 years?"

What the heck is a hectare? Everybody must be wondering this by now. Maybe you can tell us:

Challenge Question # 4
How large is a hectare? (Be sure to compare a hectare to a size people understand.)

How Many Monarchs on a Branch?
Angangueo student Blanca Medina and trees full of monarchs.

Thanks to everyone for sending the great monarch math! We wish we had room for all your answers, but here's a sample:

How to Respond to Today's Monarch Challenge Questions

IMPORTANT: Please 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 # 3 (or Challenge Question # 4)
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on February 23, 1999.

Copyright 1999 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form

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