Monarch Butterfly Update: Feb. 17, 2011
Please Report
Your Sightings!

How many monarchs are in Mexico this winter? Explore the data scientists just released. Find out how the monarch population is measured, and consider what the data mean for conservation. Begin with a bird's-eye view of a butterfly colony, and try to estimate its size!

This Week's Update Includes:

Image of the Week

Monarch butterflies in sanctuary in Mexico

How Many Monarchs?

Photo: Dr. Lincoln P. Brower, Sweet Briar College

Good News from Mexico: Monarch Numbers Are Up!

Population Up from All-time Low
Scientists announced good news from Mexico on Monday. This winter's monarch population is twice as large as last winter's. The results are a relief because last year's population was the lowest ever recorded. Take a look:

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

*One hectare equals 2.47 acres.

Look for Trends
Right now, scientists are analyzing the same data you are, and looking for trends. What trends do you see in the data? How has the size of the monarch population changed during your lifetime?

Which Sanctuaries do Monarchs Select?
Check out the map and pie chart to see which of the 12 overwintering sites most monarchs select. Which sites seem the most important to protect?

Compare This Year to Last Year
Look at two years' data on these pie charts to see if monarchs use the same sanctuaries equally each year. What new information and questions does this information raise?

What Affects Monarch Survival? Look for Factors!
Challenge yourself to identify factors that affect the monarch population size, just as scientists are doing. Taken together, factors throughout the coming year will affect the size of the next winter's population.


Graph: Monarch butterfly population in Mexico

Bar Graph
Monarch Population in Mexico
1994 - present

Did You Know?

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

Pie Graph: Monarch Butterfly Colony Selection
Map and Pie Chart
In which sanctuary are nearly half of this winter's monarchs?

Compare two years

Compare Two Years
Do monarchs use the same sanctuaries equally each year? What do these observations mean for conservation?

Journal Page: How Many Millions?

Scientists rarely say how many individual butterflies are in the colonies in Mexico. You'll appreciate why when you see how imprecise estimates based upon estimates can be!

  • Read the Story! Find out what caused scientists to raise their density estimate from 10 to 50 million monarchs per hectare.

Journal Page: How many millions of monarch butterflies?

Journal Page
How many millions of monarch butterflies?

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 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.



How many monarch butterflies this winter?

Teacher Guide

Life in the Monarch Butterfly Sanctuary Region

Monarchs Numbers Up, Tourists Numbers Down
"I have just been to El Rosario Sanctuary and we have been surprised to see the number of monarchs coming this year, begins Estela Romero. "Although the drop in tourism has been very noticeable this season, you will see many people are still visiting us, attracted by the wonderful monarch butterflies of our region. Enjoy the photos I took for you—and pack your suitcase and come to visit us!!!"


Monarch butterfly sanctuary in Mexico.

"They look so royal... we then understand why they bear such a name!!!"

Seeing Monarchs or Milkweed? Please Report Now!

All monarchs do not go to Mexico! Before spring migration begins, please help us document where monarchs are located this winter and where milkweed is available.

Map of monarch wintering sites in Mexico Pre-migration map: Winter monarch butterfly sightings (January or February) Map of milkweed emergence: Spring 2011

Mexico's Monarch Butterfly Wintering Region

Monarch Butterfly
Winter Sightings

First Milkweed
The next Monarch Migration Update will be posted on February 24, 2011.