Monarch Migration Update: April 5, 2000

Today's Report Includes:

Why Such a Slow Week for Migration?
An amazing change has occurred: We received 38 sightings during the week of March 22-28--but only one, single monarch was reported during the last week! (Thank you Travis School in the Texas panhandle!) How can this be explained?

Challenge Question #25
"List all of the possible reasons monarch sightings might have dropped from 38 last week to only 1 this week." (As always, remember to consider the behavior of monarchs AND the behavior of the monarch observers!)

The Monarch's Journey NORTH?
How far from Mexico--and in what direction--does the monarch migration advance in the spring? Imagine drawing the leading edge of the migration at different stages this spring, as the monarchs move across the Continent. Such a line is called an "isopleth", and this lesson suggests ways you can analyze the migration, using the maps we provide. See: "The Monarch's Journey NORTH?"

How Far North Would the Georgia Monarch Be?
Discussion of Challenge Question #21

Last week we asked, "If the monarch that was sighted in Demorest, Georgia (34 N, -83 W) had flown straight northward, instead of to the east, where would it be?" (Give the name of the state it would be in, and try to estimate the latitude and longitude.)

Answer: The Georgia monarch would be in Nebraska--and almost at the South Dakota border! The latitude would be about 43N, and the longitude would be 100 W. (The same longitude as the sanctuaries, since the butterfly flew due north.) The Georgia butterfly was about 2,400 km from Mexico.

To answer this question, print a copy of the Journey North map and measure the distance to GA with a string. (The butterfly did not fly over the Gulf of Mexico, so a string helps to measure the curve.) Then stretch the string straight northward from the sanctuaries--and you'll be near Springview, NE. To estimate the distance, measure the length of the string in millimeters, then use the scale bar on the map.
Take a Right Turn at the Texas Gulf Coast!
Clearly the monarchs don't go straight northward from Mexico. Instead the migration pathway seems to curve to the east, parallel with the Gulf of Mexico.

So now the question is WHY?

Challenge Question #26
"Why do you think the migration might move eastward instead of directly northward from Mexico?"

Comparing Maps
Monarch Migration and Plant Hardiness Zones

Now look at the two maps on the web. Do you see any correlation between the colored "Plant Hardiness Zones" and the path of the monarchs?
 Monarch Migration as of April 5, 2000 Plant Hardiness Zones (Click to Enlarge)

The USDA Plant Hardiness Zone map shows the lowest temperatures that can be expected each year in the United States, Canada, and Mexico. These temperatures are referred to as "average annual minimum temperatures". They are based on the lowest temperatures recorded over a period of ten or more years. For more information, visit the United States National Arboretum website.

Assuming this map also gives us an idea where spring might come earlier:

Challenge Question #27
"Name two important reasons why a vegetation map might be helpful when analyzing monarch migration."

Try This!
In your science journal, predict what you think will happen as the migration continues.

• In which Plant Hardiness Zones do you predict the monarchs will appear next?
• Each week, describe how the migration pattern compares to the Plant Hardiness Zones shown on the map.
• Suggestion: For simpler comparisons, draw "isopleths" as explained in the "Monarch's Journey NORTH?" lesson above.

Watching the Wings for Clues
Discussion of Challenge Question #20

In our March 22 update, the Aschens were carefully observing the condition of monarch wings to age the butterflies they saw along the Texas Coast. What fade value were the 3 monarchs they captured in their backyard?

Journey North students at Griswold Middle School (CT), St. Croix Falls Elementary (WI), and JFK Elementary (NY) all agreed!

 #1 #2 #3

• Monarch #1: Fade value 2, no holes, no tattering, but beginning to fade.
• Monarch #2: Fade value 0, recently emerged.
• Monarch #3: Fade value 4, very faded, some tattering and holes. Orange beginning to turn gray, black just beginning to turn charcoal, but not yet transparent or "ghostly".

Later in the migration season, it will again be important for ALL observers to note the condition of the wings. Do you know why?

Volunteer Translator Needed
Se Solicita Traductor de Ingles a Espanol

As explained in our March 29 update, we are sending weekly migration news to students in the monarch sanctuary region. We're looking for a Journey North reader who is fluent in Spanish, and is willing to proof-read the Migration News we send to Mexico each week. Because we send the update on Thursdays, the volunteer would need to review the text on Wednesday nights. (The text is only a few paragraphs long, not the full update we send to Journey North participants. Therefore, this should take fewer than 15 minutes per week.) Please contact Elizabeth Howard (ehoward@jnorth.org) if you're willing to help, or if you'd like more information. Thank you!

How to Respond to Today's Monarch Challenge Questions|