Migration Update: February 5, 2009
Please Report
Winter Sightings! >>

Today's Report Includes:

Why do these trees look orange? >>
Picture of the week
by Dr. Lincoln Brower

Welcome to Journey North! 

Welcome to our 16th 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 spectacular migration. Today's report explores an important conservation question: How many monarchs are in Mexico this winter?

Monarch butterflies east of the Rocky Mountains fly to Mexico. >>
They gather together on only twelve mountain top sites. Find them! >>
How Many Monarchs in Mexico This Year?

Scientists Measured the Population in December
The twelve major monarch butterfly sanctuaries in Mexico are measured every winter in December. These yearly measurements give scientists a chance to estimate the size of the entire overwintering population.

Everyone Expected a Small Population
Last fall at the end of the migration we asked you to predict how large this winter's population in Mexico would be. People across the monarch's range had reported low numbers during fall migration. For example, only half as many overnight roosts were reported in fall 2008 as fall 2007. Monarchs were scarce during the summer breeding season, too. Based on observations like these Dr. Chip Taylor of Monarch Watch predicted the population would measure less than 5 hectares, and perhaps as small as 3-4 hectares. Many people returned unused tags "along with short notes lamenting the lack of monarchs this past fall and requests for an explanation as to why the fall 2008 monarch population was so low," he commented in Monarch Watch Blog. So what did the scientists in Mexico find?

A Surprise!
Last week the scientists announced good news. This year's population is not as small as predicted. In fact, it is slightly larger than last year's.

Area Covered by Butterflies
Last year
4.61 hectares*
This year
5.06 hectares*

*One hectare equals 2.47 acres.

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









How does this year compare? >> Where are the butterflies? >>

Compare this year's population to those in the past 14 years. How has the size of the monarch population changed during your lifetime? >>

Nearly 75% of the monarchs are at just two of the 12 wintering sites. Find them on the map. What does this mean for conservation? >>


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 changes in the size of the monarch population.

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

Journal Page: How many millions of monarch butterflies?

How many millions of monarch butterflies are in a monarch colony? For almost twenty years scientists used an estimate of 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. >>
  • Write in Your Journal: Estimate how many millions of monarch butterflies are in Mexico this winter. >>

Journal Page
How many millions of monarch butterflies?

News from Mexico: A Report from the Field >>

Thanks to Susan Meyers and Kim Baily of "Monarchs Across Georgia" for sending this report directly from Mexico. They are leading a trip for teachers and visited two monarch sanctuaries this week, Sierra Chincua and El Rosario.

As you read: Look carefully for words that describe the monarch's habitat. Also look for details about the butteflies' behavior. These are important clues about how monarchs survive the winter in Mexico.

Report Your Sightings: Seeing Winter Monarchs or Milkweed?

All monarchs do not go to Mexico. Please help us document where monarchs are located this winter, and whether milkweed is available.

  • Please report your sightings. >>



Links: Monarch Butterfly Resources to Explore
  • Monarch Math: How many football fields would this year's monarchs cover? >>
  • Pie Chart: Where Are the Butterflies This Winter? >>
  • Pie Chart: Which Sanctuaries Do Monarch Butterflies Select? Compare Two Seasons >>
  • Journal Page: How Many Millions of Monarch Butterflies? >>
  • Journal Cover & Pages: Monarch Winter Habitat Journal >>
  • History of science: How 10 Million Became 50 Million >>
  • Overview: About Journey North's Monarch Butterfly Overwintering Study >>
  • Get Ready to Track Spring Migration: How to Watch for Monarchs >>
More Monarch Lessons and Teaching Ideas!

The Next Monarch Migration Update Will Be Posted on February 12, 2009.