Today's News Report Your Sightings How to Use Journey North Search Journey North

Monarch Migration Update: February 9, 1999

Today's Report Includes:

Get Ready to Track the Spring, 1999 Monarch Migration
Welcome to Journey North's 6th annual monarch migration study! When the migration begins in March, we hope you'll help track the butterflies' trip from Mexico. In the meantime, watch for these weekly news reports from the wintering grounds every Tuesday.

How Many Monarchs Are in Mexico?

Principal Monarch Over-wintering Sites in Mexico

Right now, the entire eastern monarch population is gathered together in Mexico. Like a snapshot in time, the winter months give scientists a unique opportunity to gather important information. But imagine if it were your job to count all the butterflies wintering in the mountains in Mexico! How do you suppose scientists go about estimating the monarch population size?

During last fall's migration, Ms. Rarick's 5 students in Franklin, TN, were among many who asked: "Where have all the monarchs gone? We used to see them everywhere-- they were very common. However, they are now scarce. Our class wants to know why." Bagensly Elementary, Franklin, TN (

Are there fewer monarchs this year? Should people be concerned? Before next week's update, look at a map of the sanctuary region and read this week's Field Notes from Mexico for clues. As a class, discuss all the factors scientists must take into consideration when making such an estimate.
Field Notes from Mexico by Dr. Bill Calvert
Dr. Calvert was among the first scientists to conduct research in the sanctuary region in the 1970's. Few people have spent more time observing monarchs there on a daily basis, so we're pleased to be able to provide you with his first-hand accounts:

February 7, 1999
Over the next 6 weeks, I'll be sending weekly observations about monarch over-wintering biology. Tomorrow will be my first day in the sanctuaries, so today I'll summarize what has most likely been happening since you tracked their migration here last fall:

When the butterflies first arrive at a sanctuary in November, they are strung out over miles of mountain ridges. Then they begin to gather into clusters, though initially the multiple clusters are not always connected. But as the temperatures drop in late November and December, the butterflies usually converge into 1 or 2 clusters (though there can be 3, 4, 5 or even more groups). Within each cluster, there is generally an area covered with tightly-packed butterflies. One gets the distinct impression that there are boundaries, even though there might be holes in the area covered, and some butterflies on the edges of the groups. A large cluster might cover 1,000--or even 2,000-- trees, but about 250 trees is more common. By mid-December the butterflies are packed into very, very dense clusters, and there are as many groups as there will be for that year (in that particular sanctuary).

In January/February, when the temperatures are the coldest, the butterflies are packed most tightly on the trees. As many as 15,000 butterflies can be on a single branch--so many that the branch actually bends under their weight! It makes you wonder:

Challenge Question #1
"If the typical monarch weighs 500 mg in January/February, how much might a branch full of butterflies weigh? (Give your answer in kilograms and in pounds. Also give name another object that weighs this amount, for comparison.)"

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

After mid-February these clusters begin to break up, or "bud", and the colonies gain area. The colonies start to split up as the monarchs spread down the canyons for nectar and water. When they come back up the mountain they don't form thick colonies any more.

Until next week,
Bill Calvert

"Field Guide" to Monarchs on the Wintering Grounds
Few people have the chance to visit the Mexican sanctuaries with Dr. Calvert. And if you visited alone, you'd wouldn't find a Field Guide for tourists with his depth of information. So why not write one this winter? Draw facts from Dr. Calvert's weekly updates, and add information and illustrations of your own. (Extra credit to anyone who writes in Spanish!)
School Weather Station to be Delivered Today
One of Dr. Calvert's first stops in Angangueo will be at Pedro Ascencio School, where he'll deliver weather monitoring equipment and data sheets. Watch for regular weather reports from the Pedro Ascencio students each week.

When most people think of Mexico, warm and sunny weather comes to mind. Those lucky monarchs! What is the climate where the monarchs spend the winter?

Challenge Question #2
"What do you suppose the high and low temperatures in the sanctuary region are at this time of year?"


  • Pedro Ascencio School is beside the Sierra Chincua Sanctuary, at 3,000 meters elevation
  • Their global address is: 19.60 N, -100.25 W
  • This is a 4 hour drive from Mexico City and 3 hour drive from Toluca
  • Check today's temperatures Mexican cities on the CNN Website

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 # 1 (or Challenge Question# 2)
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on February 16, 1999.

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

Today's News Report Your Sightings How to Use Journey North Search Journey North