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Monarch Butterfly Migration Update: April 4, 2001

Today's Report Includes:


Field Notes from Along the Migration Trail

Monarch Migration Map
as of April 4, 2001


Cold temperatures stopped the ruby-throated hummingbird migration in its tracks last week, and the same seems to be true for the monarchs concentrated in Texas. Notice how few sightings during the last week are ahead of the leading edge of the migration the week before.

If it weren't for a tiny egg sighted by Bill Stark and students at Mississippi College in Clinton, Mississippi, you couldn't add that state to your migration map.

03/27/01 Clinton, MS (32.38N, -90.34W)
"Apparently we were visited by at least 1 monarch female in the past few days. I still haven't seen a monarch on the wing but there is a fresh, white egg on a milkweed plant, A. viridis, at the Clinton (Mississippi) Community Nature Center, Clinton, MS, this afternoon. I checked the plant last Saturday and no egg was present; other plants in the center are still 'eggless.'"

At the moment we were writing this update to say how late the migration is this year--that we've always had the first reports from Arkansas and Oklahoma by now--this news arrived from Monticello, Arkansas:

04/03/01 Monticello, AR (33.58N, -91.79W)
"I saw and caught my first Arkansas monarch of the year. She was laying eggs on some tropical milkweed that I had set out a week earlier. She is a little faded, but otherwise in good shape. She has a mass of 0.60 grams and a fore wing length of 5.4 cm. This sighting is about 10 days later than the previous 5 years I've been monitoring the arrival in southeast Arkansas. Monday a warm front moved in from Texas and I thought that it might bring some visitors." Jim Edson

Temperature Maps Show South Colder Than Normal
As shown on the maps below, temperatures in Texas and across the South were more than 9 degrees (F) below normal last week, and were below normal the week before. According to Mike Quinn of Texas Parks and Wildlife, the month of March was one of the coolest and wettest on record for central Texas. Milkweed, which grows more slowly in cool temperatures, was also lagging behind. He noted, "If the Monarchs are a week LATE (emphasis added)in their northward progress by the calendar, they still could be several weeks EARLY with respect to the available milkweed."

Temperature Departures from Normal
All Maps: NOAA Climate Prediction Center

Last Week
March 25 - 31

Previous Week
March 18-24

Is the Milkweed Ready for the Monarchs?
Mike's thoughts point out how important it is to monitor milkweed while tracking the migration. 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!

Drs. Riley and Ross Still Searching in Baton Rouge
Every spring, two experts in Baton Rouge keep a careful eye on the conditions there.

"Still no monarchs," reported Gary Ross on Monday. "I spent several hours on both Saturday and Sunday in gardens around the city scouting for monarchs, but no luck. No eggs, either. However, I did notice quite a few wasps and assassin bugs (caterpillar predators) lurking about on milkweed plants in anticipation of a good meal."

Dr. Riley has not seen a single monarch yet either--even though monarchs have been sighted all winter in New Orleans, only 40 miles away. Read Dr. Riley's comments carefully. List the factors he thinks have contributed to the late arrival of monarchs this spring:

Early or Late? What's the Range, Median and Mean?
Are the monarchs really late? If so, how late? Let's find out when they normally arrive in Baton Rouge. Looking carefully at data collected in a single place helps us to be precise, and helps us draw accurate conclusions that may give us some new insights.

First some mathematical terms:
  • Range: The difference between the earliest and latest dates in a set of data.
  • Median: The median is the 50th percentile. The date in an ordered set of data such that half of the dates are earlier and half of the dates are later. Half the values are larger than the median, and half are lower. If there are an even number of values, the median is defined as the average of the two middle values.
  • Mean: The mean is the average of all the values. It's the most common measure of center. To determine the mean, find the sum of the values in the set, then divide by the number of values.

Try This!
Here are first arrival dates for monarchs in Baton Rouge: 3/3/00, 3/31/99, 3/19/98, 3/26/97. Take a close look at the data:

  1. Make a stem-and-leaf plot, arranging the data in order from earliest to latest date of sighting.
  2. Count the number of days between the earliest and latest arrival dates. This difference is the range of arrival dates for Baton Rouge.
  3. Next figure the median arrival date. Your data are already in order, so you can see on which date half of the records are earlier and half of the records are later. (Because there is an even number of records, you'll need to find the average of the two middle values.)
  4. Finally, calculate the mean arrival date. (The mean is the concept most people think of as the "average.") When using calendar dates, this can be tricky. Before reading the example on the worksheet, challenge yourself to think this through!


Now, what will happen to your analysis when THIS year's monarch arrives?

Challenge Question #18:
"How would the mean change if Dr. Ross or Dr. Riley were to see the first monarch today, April 4th?"


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

When Will the Monarchs Reach South Carolina?
Place Your Vote!

Monarch Arrival

When do you think the monarchs will arrive?

Results as of April 4th:

week of March 25-- 5 (11%)
week of April 1-- 6 (14%)
week of April 8-- 5 (11%)
week of April 15-- 8 (19%)
week of April 22-- 6 (14%)
week of April 29-- 4 (9%)
week of May 6-- 6 (14%)
week of May 13-- 1 (2%)
week of May 20-- 1 (2%)

get gear

Try this fun online poll on Ms. Thornton's 6th-Grade Science Class Web site! The class wants to know, When do you think the first monarch butterfly will arrive in Piedmont, SC? But before you vote, look at Journey North's records for South Carolina. Then adjust for this year's "late" migration, and place your vote:

When Will the Monarchs Cross Border into Canada?
This week, we challenged the students in the Mexican sanctuary schools to predict when the monarchs will cross the Canadian border, based on the migration data so far. (See below.) What do you think?

Challenge Question #19
"Based on the data so far, I predict the first monarch butterfly will cross the border into Canada on _____________ (date). The name of the Canadian Province where I think the first monarch will be sighted is _________________ )."


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

And When Will the Monarchs Reach YOU?
This is the answer everyone wants to know! You can use past years' records from Journey North's online database to find out:
  1. Record the dates that the 1st monarchs were spotted in your state/province in past years.
  2. Use the method above to calculate the mean arrival date, just as was done for Baton Rouge.
  3. Finally, consider how this year's weather might affect this year's migration.

To Access the Journey North Migration Data
From any Web page, hit the owl button as if to "Report Your Sightings." On the bottom of the page, go to "Visit the Journey North Archives." You'll find the monarch migration records there, organized by month.

Alternatively, use the GIS Map Server for a visual way to gather and analyze the data:

Noticia de la migracion de la mariposa monarca
3 abril de 2001
As the butterflies fly over your homes, schools and cities, we're sending the news back to the students in Mexico so they can track the migration too. Here is this week's report in Spanish, with an English translation:

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: jn-challenge-monarch@learner.org
2. In the Subject Line of your message write: Challenge Question #18 (or #19)
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on April 11, 2001.

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

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