Migration News: October 27, 2006
  • This Week: A Navigation Mystery--The Migration Through Mexico

The monarchs are now crossing Mexico, where food and water can be scarce.

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Eight days after a cold front pushed spectacular numbers of monarchs across west Texas, they cruised into northern Mexico, 200 miles to the south. But this time, people saw "miles y miles de mariposas monarcas" and said a "frente frio" was responsible.

"¡POR FIN LLEGARON!" they said. "At last they are arriving!"

Special thanks to Rocío Treviño of Correo Real for forwarding these spectacular observations from northern Mexico this week!

  • First-hand observations(in Spanish) >>

Crossing into Mexico

People entering Mexico must go through customs. Monarchs can fly between the countries without stopping!

The Rio Grande River is the Border

In Texas, the Rio Grande River marks the border between the U.S. and Mexico. Above: As seen between Del Rio, Texas, and Acuna, Coahuila.

The Exact Line

On the international bridge between Del Rio and Acuña, this line on this sign declares the exact border between the United States of Mexico and America.

This Week: A Navigation Mystery--The Migration Through Mexico

The map below shows the route the monarchs probably take as they cross Mexico. It is based on observations made by biologist Dr. Bill Calvert--and many others--during fall migration. The direction the monarchs travel is "delightfully confusing!" says Dr. Calvert. The map illustrates a mystery of monarch navigation.

Take a look: The monarch's winter home is directly south of the region in Texas (centered on Del Rio) where most monarchs cross the border into Mexico. However, the monarchs don't travel straight south as they cross Mexico. Study the map and notice the way the monarchs travel instead. Compare the line of longitude -100 West to the path of the migration.

Think about this question:
Why don't the monarchs travel straight south as they cross Mexico?
(Click to see larger map.)

Then read Dr. Calvert's description >>

Teachers' Guide

The suggestions in this guide are provided to help teachers integrate Journey North's real-time program in the classroom.

Also: Migration Rate Math: Here is this week's collection of quantifiable monarch observations: Who saw the strongest migration this week?

The Next Monarch Butterfly Migration Update will be posted on November 3, 2006

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