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Monarch Migration Update: March 16, 1999

Today's Report Includes:

Field Notes from Mexico by Dr. Bill Calvert
15 March, 1999

The Monarchs Are On Their Way!
The monarchs are now definitely leaving! In the town of Angangueo, one can almost always see them during the sunny part of the day--many high in the sky, drifting lazily northward, setting out on their long journey.

Up higher at the sanctuaries, monarchs pour out of the colonies during these warm, sunny days. (See temperatures reported this week by Pedro Ascencio school.) The intense radiation serves to warm the monarchs' muscles so they may fly long distances. Some are seen miles from the colonies taking nectar from the now abundantly flowering composites (Eupatorium and Senecio).

The El Rosario colony now occupies double the area that it did in February. And, to the delight of the tourists, the butterflies flood the area below the colony where the concession stands are located. The colony has shifted down and to the west. Strangely, the thick clusters once present at the very top of the colonies have moved around, not down, to the east side of the Arroyo el Canejo--a change of position of about 100 meters.

At Sierra Chincua, the colony is now a string of pears spread out on the north side and on the bottom of the Barranca Honda. (Eligio Garcia reports that he is no longer able to measure the colonies because the butterflies are very dispersed and inaccessible.) The Sierra Chincua continues to move down the Barranca Honda. Paradoxically, remaining butterflies in both sanctuaries are sitting in positions where they receive the hottest afternoon sun.

Within the colonies, mating "take downs' are occurring more frequently. Most pairs break apart just as they strike the ground. Only about 10% of the take down pairs actually couple because, when located in the shaded part of the forest, the male is too cold to fly off with the female. If on a trail,they struggle in the dust.

Challenge Question # 14
"Do you think being covered with dust harms the monarchs? If so, how?"

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

In the early mornings, butterflies pour into the fields to drink. I have noticed that they concentrate on the sunny side of a shaded patch, in a narrow band only 1-1.5 meters wide. I suspect they're drinking dew there, just before it evaporates in the strong tropical sun. (The monarchs can't seem to function well in the shade, so they move in this narrow band of sunshine where the sun hasn't yet evaporated the dew.)

March days are brilliant and sunny in Michoacan. The shadows cast by the tropical sun are especially dark, and the contrast between sun and shade is especially intense.

Challenge Question # 15
"Can you think of some reasons why the sun is so brilliant here?"

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

I'll be here just one more week, then heading north along with the monarchs.

Until then,
Bill Calvert

Texas Monarch Sightings Present a Challenge
During the last week, seven monarch sightings were reported from Texas. In last week's report, we provided data showing where over-wintering monarchs had been seen this year. Comments from observers in Texas are provided below, and here are this week's data:

Consider this:

Challenge Question # 16
"Will you include today's Texas monarch sightings on your migration map, or do you think they are sightings of local monarchs? Explain your reasons in your answer."

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

You're the Scientist
Each year as we begin to track the migration we remind you that you must decide how to interpret observations provided by your colleagues. (Journey North carefully scrutinizes data and removes obvious errors before including in our updates.) However, as a scientist, you are responsible for questioning, validating and interpreting these data.
As you track migrations, you will be receiving data from observers across the continent. While the Internet gives us the opportunity to expand our own observations in ways never before possible, order for the data to be valid and useful, we must be able to trust the accuracy of observations made by others. Here's a classroom lesson centered on this issue:

Comments From Texas Observers
Mr. Johnny French, of the U.S. Fish and Wildlife Service's Field Office for Ecological Services, in Corpus Christi, reported the first monarch of the season last Wednesday, March 10. He monitors the butterfly garden at Texas A & M University daily: "Since my first sighting last week, I've gone from seeing no monarchs to seeing one per day."

"My wife and I saw what MIGHT have been two migrating monarchs, and not the "coastal" monarchs we have had all winter in Port Lavaca," wrote Harlan Aschen. While driving the 30 miles from Victoria to Port Lavaca, the two monarchs passed in front of their van, heading northward. "We are visited daily by the Monarchs that have been over-wintering along the Gulf coast. We have seen many faded and tattered Monarchs during the winter and wonder how we will tell the difference between those that have been around HERE for weeks and those arriving from Mexico. It was a mild winter with the Asclepias curassavica growing and blooming all winter. We found some wild Asclepias viridis about 4 inches tall in the pasture last week, so nature is making ready."

Other factors to consider:
  • Many monarchs were sighted north of the over-wintering area on March 1, flying northward.
  • No monarch sightings have been reported yet from the many Mexican observers who participate in "Correo Real" program. These observers are located in the Mexican states north of the over-wintering area and south of the U.S. border.
  • We asked Bill Calvert, himself a Texan, how he would interpret these early Texas observations: "They could very well be migrants, but it's a bit confusing. It would be interesting if somebody were monitoring egg loads see if there is an increase. When the egg load increases dramatically (meaning a shift from an occasional egg to 2-3 eggs on a plant) that's a sure sign of the returning migrants. I would also want to have some assessment of their condition. You'd expect a local breeder to be in better condition than one that's flown thousands of miles. But it may be that there's no difference; local monarchs at the end of their tenure might be tattered as well. But these are very hard questions and it's a bit confusing."

How to Respond to Today's Monarch Challenge Questions

IMPORTANT: Please 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 # 14 (or Challenge Question # 15 or #16)
3. In the body of EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on March 23, 1999.

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