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Monarch Butterfly Migration Update: April 11, 2001

Today's Report Includes:

Monarchs Surge into Oklahoma, Arkansas, and Louisiana!
What a change we've witnessed during the last week. The leading edge of the migration hadn't moved beyond northern Texas (33N) for almost two weeks. Between April 4-8, a sudden influx of sightings arrived from Oklahoma, Arkansas, and Louisiana.While we don't know how far a single butterfly traveled in a day, we can see that the migration front advanced some 200-250 miles, to about 36N in Oklahoma:

Measuring from Dallas, Texas:
  • to the Mountainburg, Arkansas sighting on April 4: 250 miles (402 km)
  • to the Wagoner, Oklahoma sighting on April 8: 236 miles (380 km)

Monarch Migration
as of April 11, 2001

Monarch Migration Map
as of April 4, 2001

Beginning on April 1st, low pressure to the northwest of Texas kept south winds blowing for 9 consecutive days through Texas and northward. Visit the Weather Map Archives and see if you can see evidence of south winds on April 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, and 9th! (Also check temperatures and sky conditions before and after April 1st.)

Is the Milkweed Ready for the Monarchs?
How does the readiness of monarch habitat affect the pace of the migration? How will the availability of milkweed affect the reproduction of the next generation?

These are critical questions. Please help find the answer! Keep a close eye on the sky for monarchs--and an eye underfoot for milkweed. Here's the latest milkweed map:

Please report the FIRST MILKWEED to Emerge This Spring!

The Monarch's Journey NORTH?
Analyzing Spring Monarch Migration Patterns

Now that the migration is spreading out from Texas like a huge fan, plan to analyze the pattern each week. Imagine drawing the leading edge of the migration at different stages as the monarchs move across the continent. Such a line is called an "isopleth," and this lesson walks you through the steps.

Predicting the Route of the Monarch's Spring Migration
As you analyze the data each week, continue to revise your predictions as to where the monarchs will appear next. Record the arrival dates and the order of states/provinces on your Monarch Spring Migration Route Prediction Chart.

Discussion of Challenge Question #17
We asked you to, "Send your list of the 15 states where you think the monarchs will appear next. Why do you think the monarch migration will arrive in the states in the order that you predicted? Explain your reasoning!"

Here's the predicted path from the Fourth grade class at Sterling Memorial School in Oneco, CT. How does their prediction compare to yours? What have we learned from this spring's migration records so far?

"We think that the states that the Monarchs will travel to next are: Oklahoma, Mississippi, Alabama, Arkansas, Georgia, Tennessee, New Mexico, Arizona, South Carolina, Kentucky, Kansas, North Carolina, Missouri, Virginia, Illinois. The reason we picked the states in this order is because the monarch's will follow the warming weather as it spreads north."

What About the Sighting from Athens, Georgia?
Today's map contains a big surprise--do you see the sighting in Athens, Georgia? Athens is over 400 miles (644 km) east of the leading edge of the migration. It's also 275 miles (443 km) north of the nearest Florida sighting. The observer was Elizabeth King, a teacher who was trained last summer at a "Monarchs in the Classroom" workshop. Here are her comments:

04/08/101 Athens, GA
"Unbelievable! At approximately 5:40pm, I witnessed a large monarch cruising NE 3 to 4 feet over an open field of our property. Weather was mostly sunny, calm with slight breezes and 86*F. I'm so excited! I am absolutely sure it was a monarch. In fact, yesterday (04/09/01) I spied yet another. A good-sized Monarch on a north-westerly heading cruising approximately 40-50 ft. it seemed to be taking advantage of the breezes, as it would flap a couple times then sail. Weather was a warm but calm 86*F with light breezes. There are now 32 milkweed sprouts in my garden. Asclepias tuberosa (butterfly weed) began sprouting shoots on March 13th. By March 28th, A. tuberosa sprouts had grown to about 1 1/4 inches. Northeast Georgia is finally on the map!!

You're the Scientist: Evaluating Data Collected by Peers
When unusual or surprising sightings occur, what questions come to mind? Listen to your questions! Write them down! Don't simply take our word for it! Good scientists always question the data. Before you add migration sightings to your map, make sure you trust the accuracy of the information.

Remember: All sightings and observers' comments are available on the Journey North Web site. Come to the web and read them. If you still have questions, contact the observer by e-mail. The lesson "You're the Scientist" explores ways people question information, and how they decide what sources they believe. Remember, this is your study and...

Challenge Question #20
Now you must decide whether to add the Athens, GA sighting to your migration map!
  1. List all of the factors that you think make the sighting believable
  2. List all of the factors that you think make the sighting doubtful

Challenge Question #20:
"Will you add the Athens, Georgia sighting to your migration map? Why or why not?"

(To respond to this question, please follow the instructions below.)

The Count is In:
How Large Was This Winter's Monarch Population?

Each week, you've received Eligo Garcia's measurements from one sanctuary, the Sierra Chincua. We've seen how the numbers of monarch trees varies over time, and how much the colony moves. Once every winter, all of the colonies are measured. This is done in December, because during the coldest time of year the butterflies are clustered together most tightly.

Like a snapshot in time, the annual winter measurements give scientists a chance to estimate the size of the entire over-wintering population. Here are this winter's measurements, thanks to Eligio. The data show the surface area each colony covered, in hectares:

Size of Over-Wintering Monarch Population
(Monarch Coverage in Hectares)









Sierra Chincua








El Rosario








*Other 3 Sanctuaries
















*Note: The "Other 3 Sanctuaries" are Chivati, Cerro Pelon and Altamirano. So that the years can be compared, we have excluded data from some of the smaller colonies (such as San Andrés, Piedra Herrada, San Fco. Oxtotilpan and Palomas) for which data was not consistently collected every year.

How Many Monarchs in Mexico This Year?
As a rule of thumb, Dr. Calvert estimates that there are 13,000,000 monarchs per hectare. Using this figure, you can estimate the number of monarchs that over-wintered in Mexico this year. You can also compare the population size from one year to the next.

Challenge Question #21
"According to the data provided by Eligio Garcia, and Dr. Calvert's estimate of 13,000,000 monarchs per hectare, how many monarchs do you estimate were in Mexico during each of the past 7 years? How does this year's population size compare to other years'?
  • 2000/2001
  • 1999/2000
  • 1998/1999
  • 1997/1998
  • 1996/1997
  • 1995/1996
  • 1994/1995
(To respond to this question, please follow the instructions below.)

Try This! Suggestions for Analyzing Population Data
Graph the population data from the winter of 1994/1995 to the present. Then answer these questions:
  • In which year was the population the highest during the past 7 years?
  • In which year was it the lowest?
  • Calculate the average population size, based on 7 years' data?
  • How does this year's population compare the average?
  • Describe this year's population as a percentage of the highest and lowest years.
  • Look at data from the two largest sanctuaries, Chincua and El Rosario. How much do the sizes of the colonies vary from year to year?
  • Which sanctuary would you say in the largest, based on 7 years' data?

Discussion of Challenge Question #16
Unlike people, who take care of their offspring for at least 18 years, a female butterfly's job as a parent is finished as soon as she lays her eggs. Females typically lay only one egg per plant. (When you find multiple eggs on a plant, they were probably laid by different females, with each butterfly laying only one of the eggs.)

Challenge Question #16 asked, "Why do you think female monarchs avoid laying more than one egg on a milkweed plant?" Students from Ohio to Maine put their heads together and came up almost a dozen reasons why. Their answers show an understanding of such ecological concepts as predation, competition between different species (inter-specific competition) and competition between individuals of the same species (intra-specific competition). Here are the reasons they think females lay one egg per plant:
  • So the larva has enough milkweed to eat.
  • So each baby can have more food and nutrients
  • If a plant is destroyed only one baby is lost, not many
  • Because after the eggs hatches, the caterpillars are very, very hungry. They eat, and eat, and eat. If more than one caterpillar is sharing the milkweed plant, they will be competing for the same food source and may not have enough for everybody.
  • Because if that plant is destroyed...phoofff all her hard work is gone.
  • So that anything that starts eating the milkweed would only destroy one egg.
  • If one of the eggs were to hatch a few hours ahead of the other ones, it would probably eat them to get the nutrients from the eggshells of the others.
  • So that when the larva emerges it would not fight with another larva.
  • Because they might fight over the milkweed.
  • Because they might eat each other.
  • If predators are near they can eat only one egg instead of them all.

Thanks to these students for sharing their thoughts!

  • Mrs. Grimm's 5th grade class, Kidron, OH
  • Mrs. Millard's Class, Roosevelt School, River Edge, NJ
  • Jimmy S. of Ms. Allen's class, Village Elementary School in York, ME
  • Ms. Ockene's 5th graders, Heath School, Brookline, MA
  • Mrs. Sheer's 4th grade class, Glenwood Elementary, Chapel Hill, NC
  • Mrs. Dempsey's Second Grade, Charlotte Dunning School, Framingham, MA
  • Jamie M. and Amy P. (School and location not provided)

Some butterfly species commonly lay multiple eggs--even masses of eggs--on a single plant. This strategy has its merits too, as Mrs. Dempsey's Second Grade could imagine:

  • If a predator eats some eggs, a few would still be left.
  • Maybe a predator might think [the eggs] are just a disease on the plant.
  • Some might die after they are caterpillars and then some would be left to live.
  • The mother lays the eggs on the milkweed when the leaves are little, and when they hatch, the milkweed will be big and they don't have to worry about having enough to eat.
  • If there is not much milkweed, the mother may think she can only pick one plant because the other monarchs might need room for their eggs.

How to Respond to Today's Monarch Challenge Questions:

IMPORTANT: Answer only ONE question in each e-mail message.

1. Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question #20 (or #21)
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on April 18, 2001.

Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form

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