FINAL Migration Update: November 11, 2010
Please Report
Your Sightings!

We ushered the monarchs across the continent, and together we told their story. They flew overhead, rested overnight, and feasted on flowers as they traveled. The monarchs are arriving in Mexico now, and we end the migration season with a key question: How many monarchs made it to Mexico, and how is the population faring?

This Week's Update Includes:


Image of the Week
Roosting Monarchs: Preparing for Take-off

How many made it to Mexico?

News: The Overwintering Season Begins!

The Data Everybody's Waiting For...
Every December, when fall migration is over and the monarchs are clustered tightly in their winter colonies, scientists make an important measurement. They visit the monarch's 12 traditional wintering sites and measure the size of the colonies. (See map.)

This chart shows the data scientists have collected over the past 16 years. Notice last year's measurement. The population was the smallest ever recorded in 16 years of keeping records!

What will the scientists find this year?
That is the question on everybody's mind. Did the monarchs have a productive breeding season in the north? How many survived the long fall migration?

Scientists are waiting with great interest to see what this year's results will show. The measurements made in Mexico are the most reliable estimate we have of the size of North America's monarch population. Like a health check-up or a report card, the results tell us how the monarchs are doing.

Mexican biologist Eduardo Rendon of the World Wildlife Fund is the scientist who will lead the team. He will share his data with us when Journey North begins in February. (Watch for our first update on February 4, 2011.)

Any Predictions?
After following this fall's migration, how large do you predict this year's population will be?

Here's what we noticed about this fall's migration: People across the north said they saw lots of monarchs this summer. The breeding season seemed productive. When the migration season began unusually high numbers of monarchs were reported, especially at roosts in the Great Lakes region. However, by the time the migration reached Texas and northern Mexico, the observations people reported were not unusually high. In fact, they were somewhat lackluster. So where did all of the monarchs go?

  • Did the butterflies fly overhead and travel to Mexico largely unnoticed?
  • Did the large numbers of monarchs migrating along the Atlantic coast get swept out over the ocean?
  • Why were so many monarchs sighted in the Gulf coast states this year? Had they been blown down from the Midwest where south winds were persistent this fall?

Nobody knows answers to these questions, but the observations citizen scientists contribute each fall broaden understanding. Thank you for sharing your own observations!

Still Seeing Monarchs? Please Let Us Know!
Last Friday on the Texas Gulf coast was the one of the season's biggest migration days yet, with 600-1,000 monarchs passing per hour.

How long will monarchs continue to vacate the north? Tell us what you see! These observations are valuable, so please help us document when and where monarchs are present.

Graph of monarch butterfly population in Mexico.

The Data Everybody's Waiting For...


Did You Know?

A monarch colony contains 10-50 million butterflies in 1 hectare of forest.

How many monarchs do you estimate each winter's population contained, according to the chart?


Mexican monarch butterfly biologist, Eduardo Rendon
Eduardo Rendon
Mexican biologist Eduardo Rendon is the scientist who leads the team.


Map of monarch butterfly sanctuary region.

Mexico's Monarch Butterfly Overwintering Region



Traveling With a Monarch: Tell the Story of Fall Migration

What have you learned as you traveled with monarchs on their two month, 2,000-mile journey? Tell the story of the monarchs amazing tale of survival.

Ways to tell the story:

  • Write and illustrate a book.
  • Make a "travel brochure."
  • Create a poster or display.
  • Develop a lesson to teach younger kids.

Here's a checklist for your project and a map you can draw on.

Checklist Map
The Migration: Maps and Journal Page 
Map of All Monarch Butterfly Sightings: Fall 2010 Map of Monarch Butterfly Roosts: Fall 2010 Migration Journal Page

ALL Monarch


Fall Roosts


For Your Journal
This Week's Questions

Still Seeing Monarchs? Please let us know!

This is the FINAL fall Monarch Migration Update. See you in February, 2011!