Migration Update: February 7, 2008
Please Report
Winter Sightings! >>

Today's Report Includes:

  • Welcome to Journey North! >>
    • How many monarchs this year? >>
    • Are there as many as last year? >>
    • Where are the butterflies? >>
  • Slideshow: How do scientists measure the colonies? >>
  • Challenge Question #1
    • How many individual butterflies? >>
  • Seeing Monarchs?
    • Please report your sightings! >>
  • Links: Monarch Butterfly Resources to Explore >>


Butterfly Trees! >>
Picture of the week
by Dr. Lincoln Brower

Welcome to Journey North's spring season! 

Welcome to our 15th season of tracking the monarch's spring migration. When Journey North begins every February, the monarchs are at their winter home in Mexico. As we wait for their migration to begin in March, our weekly updates focus on the theme of survival. The monarch's ability to survive the winter in Mexico is as remarkable as their migration. Today's report explores an important conservation question: How many monarchs are wintering in Mexico this winter?

Monarch butterflies east of the Rocky Mountains fly to Mexico. >>
They gather together on only twelve mountain top sites. >>
How many monarchs in Mexico this year?

The twelve known monarch butterfly colonies in Mexico are measured every winter. These yearly measurements give scientists a chance to estimate the size of the entire overwintering population.

This year's butterflies cover
4.61 hectares*
That's equal to
11 football fields!

Mexican biologist Eduardo Salinas-Rendon led the team that measured the monarch population this winter.

As many as last year? >> Where are the butterflies? >>

Are monarch numbers rising or falling? Compare the 2008 population to those in the past 13 years. >>

Over half of the monarchs are at just two of the wintering sites. Find them on the map. >>


How do scientists measure the colonies? >>

Scientists want to know if we are doing a good job protecting monarchs. Because the monarchs in Mexico have come from across eastern North America, the winter measurements have extra meaning. Scientists watch these numbers carefully and try to understand what causes the changes they see.

Today, see how the scientists measure the monarch colonies, and try making some measurements yourself. >>

Challenge Question #1: How many individual butterflies?

Scientists don't know how many individual butterflies are in the monarch sanctuaries. For almost twenty years the scientists' best estimate was 10 million monarchs per hectare. Then something happened.

  • Read the Story! Find out what caused scientists to raise their estimate to as high as 50 million monarchs per hectare. >>
  • Then Try Challenge Question #1: There are 4.61 hectares of monarchs this winter. If there are 10 million monarchs per hectare, how many butterflies are there? What if there are 50 million monarchs per hectare?

To respond: Write in your journal and send us your answer for possible inclusion in next week's update. (Don't forget to tell us your name and school!)

Seeing Monarchs? Please report winter sightings!

All monarchs do not go to Mexico. Please help us document where monarchs are located this winter. These observations are important as we watch for ways climate change could effect the monarch's range and migration.

  • Please report your sightings. >>


Links: Monarch Butterfly Resources to Explore
  • Math: How many football fields would this year's monarchs cover? >>
  • History of science: How Many Millions of Monarchs? >>
  • Journal: Monarch Winter Habitat Journal >>
  • Overview: About Journey North's Monarch Butterfly Overwintering Study >>
  • Get Ready to Track Spring Migration: How to Watch for Monarchs >>
  • Get Ready to Map the Migration: >>
More Monarch Lessons and Teaching Ideas!

The Next Monarch Migration Update Will Be Posted on February 14, 2008.