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.
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I'll be here just one more week, then heading north along with the monarchs.
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:
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:
How to Respond to Today's Monarch Challenge Questions
1. Address an e-mail message to: email@example.com
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