Monarch Update: February 4, 2010
Please Report
Your Sightings!

Welcome to Journey North's 17th season! Three months ago, the first monarchs reached their winter home in Mexico after a long, fall migration. How many monarchs made it to Mexico — and how are the butterflies doing? This week, explore the population data scientists have just collected. Find out how scientists measure the size of the monarch population and what the data means for conservation.

This Week's Update Includes:

Image of the Week

How many monarchs?

Photo: Dr. Lincoln Brower, Sweet Briar College

News: Scientists Measure Monarch Population

Population at an All-Time Low
The twelve major monarch butterfly sanctuaries in Mexico are measured every winter. These yearly measurements give scientists a chance to estimate the size of the entire migratory population.
Scientists announced the results in January. This year's population is the smallest ever measured since monitoring began in 1994. Take a look:

Area of Forest Covered by Butterflies
Last year
5.06 hectares*
This year
1.92 hectares*

*One hectare equals 2.47 acres.

Did You Know?
Although monarch butterflies are not an endangered species, their migration is considered an endangered phenomenon. Scientists wait with anticipation for the winter population estimates to be released every year. Like a yearly check-up, the measurements indicate the overall health of the migratory population. The number reflects survival and reproductive success over the past year.
Scientists watch these numbers carefully and try to understand what causes changes in the size of the monarch population.

What Affects Survival? Look for Factors!
As you study monarchs with Journey North this winter and spring, focus on the theme of survival. What threats do you think monarchs face at the overwintering sites in Mexico? What challenges will they face during spring migration? Next spring and summer, what will affect the monarch's ability to survive and reproduce? Taken together, factors throughout the monarch's annual cycle will affect the size of the next winter's population. Challenge yourself to identify factors that affect the monarch population size, just as scientists are doing.

Bar Graph
Monarch Population in Mexico
1994 - present

Monarch Butterflies!
One bough can hold 15,000 monarch butterflies

map of monarch wintering sites in Mexico

Mexico's Monarch Butterfly Wintering Region

Slideshow & Teacher Guide: How Many Monarchs This Winter?

Look at a monarch colony from the air and imagine counting millions of monarch butterflies. Take a walk into the forest and see how scientists actually measure the monarch colonies!

Teacher Guide
This new Teacher Guide provides a framework for exploring monarch population data from Mexico. Students use actual data from current research. They investigate how scientists use the data to reflect on past events, assess current trends, and make predictions for the future. The activities put this year's population data into perspective and help students see why monarch population studies are so important.

Teacher Guide

Journal Page: How Many Millions?

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.

Journal Page
How many millions of monarch butterflies?

Seeing Monarchs or Milkweed? Report Now

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



Research Question and Links: Explore!

This Week's Research Question:
Why do scientists often say they don't really know how many monarch butterflies are at the overwintering sites in Mexico?

Explore these links to do your research:

Additional links to explore:

More Monarch Lessons and Teaching Ideas!

The Next Monarch Migration Update Will Be Posted on February 11, 2010.