Teacher Guide: How Many Monarchs This Winter? Estimating the Size of the Monarch Population in Mexico

Teaching Suggestions
How Many Monarchs This Winter?
Estimating the Size of the Monarch Population in Mexico
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Summary
Every year monarchs migrate to Mexico from across eastern North America. They cluster by the millions in 12 mountain sanctuaries. Because the butterflies are gathered in one small region of Mexico, scientists have a chance to estimate the size of the entire migratory population once each year. Students analyze authentic data through graphs, maps and charts to explore the essential question:

Essential Question
Why is it important to collect and analyze monarch population data from year to year?

Slideshow/Booklet

Lesson Goals and Objectives:

Lesson Goals

Explore how scientists estimate the size of the monarch population in Mexico's overwintering region each year.
Investigate questions about why monarch population studies are important; how scientists use the data to reflect on past events, assess current trends, and make predictions for the future.
Broaden students’ awareness of monarch population questions and concerns.

Lesson Objectives
After reading the slideshow and completing the follow-up activities, students will:

Describe what a monarch population estimate is.
Explain why scientists collect and analyze monarch population data each year.
Write analysis statements that accurately describe this winter's population using actual data, charts, graphs and maps.
Pose questions and possible explanations for the population findings collected and graphed from 1994 to the present.

Page-by-Page Planning Guide

Experience the text first as a reader and then as an instructor. As you read through the slideshow/booklet text, use this planning guide to capture your thoughts: observations, questions, discoveries, vocabulary, possible teaching applications, etc. Share your thinking process with students to model effective reading strategies.

Page-by-Page Planning Guide

Planning Guide

Step-by-Step Instructional Plan

Pre-Reading: Set the Stage for Learning

1. Invite students to examine the cover photo of the slideshow/booklet with the aerial view of a monarch colony. Ask students to guess why the trees look orange. Explain that this is a monarch butterfly colony! Ask: How many butterflies do you suppose are in this picture?

Explain that scientists have just finished estimating the size of this winter's monarch butterfly colonies in Mexico. Break students into groups. Have each group decide how they could estimate the number of monarchs they see in the photo. Ask: How would you use this photo to estimate the number of butterflies in a monarch sanctuary? How do you suppose scientists do this important job? Have students estimate how many individual butterflies are in the picture and explain the procedure they used to make their estimate.

Photo: Dr. Lincoln Brower
Sweet Briar College

Aerial view of a monarch colony.

Map
Mexico's Monarch Butterfly Wintering Region

Reading/Viewing the Slideshow

As a class read through the pages of the slideshow together, stopping occasionally to spotlight key ideas and ask questions. Encourage students to share questions sparked by the information and images.

After Reading: A Closer Look at Monarch Data

As you prepare students to look at the data on graphs in this lesson, explain:

"Right now, scientists are looking at the same data you are about to see. They use this data every winter like a 'report card.' It tells them how the monarchs have been doing over the past year. Scientists must consider causes for any changes they see."

Place students in small groups. Distribute one or all of the three graphs below.

Encourage students to share interesting and surprising findings from the graphs and charts.
Invite students to pose questions.
Challenge students to write discovery statements and/or comparison statements to summarize what they learned from the graph.
Chose from a brainstorm list of Guiding Questions to help students explore the graphs in this lesson.

Guiding Questions

1. Population Bar Graph: How Many Monarchs This Winter?

This graph shows winter monarch population estimates from Mexico from 1994 to the present.

Sample questions to use with this graph:

What information does the graph show?
Based on the graph, in which year was the population the highest? The lowest?
How does the size of this year's population compare to those in previous years?
Why do you think it's important to measure the monarch population every year?
For more samples, see Guiding Questions.

Population Graph
How many monarchs this winter?

2. Map and Pie Chart: Which sanctuaries do the monarchs select?

This map shows the location of the monarch's 12 major overwintering sanctuaries in Mexico. Each sanctuary is marked with a colored circle. The pie chart shows what percent of this year's monarch population is using each sanctuary.

Sample questions to use with this graph:

Which sanctuary did most monarchs select this year?
What factors might influence why monarchs use one sanctuary over others?
How do you think scientists could use the information on this map and graph?
For more samples, see Guiding Questions.

Map and Pie Chart
Which sanctuaries do the monarchs select?

3. Pie Charts: Compare Two Winter Seasons

These pie charts show how the monarchs were distributed last year and this year. The measurements are taken each year in December.

Sample questions to use with this graph:

What new information do you gain by comparing last year's data to this year's?
Why is it important to have information about the percent of monarchs in each sanctuary from more than one year?
What mistakes might scientists make if they had information from only one winter?
For more samples, see Guiding Questions.

Pie Charts: Compare Two Years
Do monarchs select the same sanctuaries every year?

4. Wrap Up: Summarize Learning

Use questions to help students summarize and extend their learning:

How do scientists describe this year's monarch population in Mexico this year?
Why do you think scientists collect information about the number of monarchs at the overwintering sites every year?
Scientists can't predict which sanctauries the monarchs will select use in any particular year. How do you think this makes conservation decisions difficult?

Challenge students to imagine they are scientists and have them present the population data collected this year in a creative way.

Did You Know?

Although monarch butterflies are not an endangered species, the migration is considered an endangered phenomena. These winter population measurements are the best indicator of the monarch population's status, so scientists wait every year with anticipation for the results to be released.

Related Journey North Lessons and Links

1. Story and Journal Page: Changing Estimates

Story
Scientists really don't know how many individual butterflies are in a monarch colony. For almost twenty years, their best estimate was 10 million monarchs per hectare of forest. Then something happened that caused them to raise their estimates 5 times higher, to as many as 50 million monarchs per hectare.

Story
How 10 Million Became 50 Million

Journal Page
How many millions of monarchs are in Mexico this winter? Use this journal page to help students estimate the number of butterflies based on two different monarchs-per-hectare estimates. Reflect on why scientists often say that they don't really know how many monarch butterflies are in a monarch colony.

Journal Page
How many millions of monarch butterflies?

2. How Many Football Fields Would the Monarchs Cover?

How many hectares (or acres) of forest are filled with overwintering monarchs? Try this math activity to find out:

How Many Football Fields Would the Monarchs Cover?