Monarch Migration Update: March 23, 1999
Today's Report Includes:
More Monarchs Sighted in Mexico & Texas
Rocio Trevino wrote from the Correo Real monarch migration program in Saltillo, Coahuilla, "You were right about the return of the monarchs, they were passing by my head and I had not noticed." (See sightings provided by Correo Real below.)
Further up the trail in Port Lavaca, TX, Harlen Aschen wrote on Sunday, "We FINALLY think we've seen a migrating monarch! It was very, very faded with 4 or 5 small holes in the wings that you could see the sky through. It flew off to the NNE into a gentle north breeze."
Here are today's data--NOW do you think the monarchs are migrating?
Final Field Notes from Mexico by Dr. Bill Calvert
This is my final report from Mexico as I'll be heading home next week. I will send my next report when I'm back in Austin.
A Quiet Departure This Year?
Nobody has witnessed masses of monarchs flying away this year. Dr. Lincoln Brower drove across the flyway on Sunday, March 21, and counted only 140 monarchs between Toluca to Zitacuaro. During the past week, we have traveled the area immediate north of the colonies of Herrada, Oxtotilpan, El Pelon and more recently Chincua, Rosario and San Andreas. The numbers seen traveling north have so far been disappointing, especially in the areas north of the southern colonies (Herrada and Pelon).
Nevertheless, Eligio Garcia reports that most monarchs have in fact departed. No butterflies are left in Herrada or Las Palomas, there are "precious few" in Picacho, and "very few" at El Rosario and Chincua. Last Friday at El Rosario, butterflies remained on only 25 of the 740 trees they covered during the peak of winter.
Physical Condition of the Butterflies as They Leave Mexico
What do the monarchs look like at this time of year, as they set off on their long trip northward? From an average mid-winter weight of 500 mg, the average weight is now down to about 400 mg. However, the departing monarchs APPEAR to be in remarkably good condition. Considering they have already flown as much as 2,000 miles and endured 5 months in Mexico, there is really not much sign of wear as they depart the colonies. However, for reasons I don't understand, when they appear in Texas a few weeks later, their wings are often so faded as to appear ghost-like. It seems that a lot of wear occurs on the trip north. I'm just speculating, but for some reason the heat and direct sun on the return journey seems to cost them a lot, perhaps because the sun is so strong at this latitude in March. (See below.)
Hot & Dusty Along the Migration Trail
I understand there are drought conditions in northern Mexico and Texas. Rocio Trevino noted the conditions in her region: "The weather is dry, windy and dusty." According to the Texas State Climatologist, John Griffiths, precipitation was way below normal for almost all of Texas during February. (See map of precipitation in Texas during February)
Discussion of Challenge Question #11
A few weeks ago, I asked if you could think of another cause of cascading that could be due to the presence of people? Here are the ideas sent by students:
All of these are good guesses. But Joshua and Jessica at Citrus Elementary School
in Vero Beach FL, thought of my answer: Carbon dioxide (CO2).
Subtropical Sun and Shadows
Challenge Question # 15
"Can you think of some reasons why the sun is so brilliant here in March?" There are a number of reasons, but the 3 of most importan are:
Until next week,
Weather Report from Escuela Pedro Ascencio
Profesor Gilberto Salazar Vargas reports that it rained on Saturday for the FIRST time in over 30 days, when just 2 cm rain was received. Also, on Sunday the town of Angangueo celebrated the first day of spring, and the final day of the monarch festival. The entrance to Sierra Chincua was officially closed.
Plot last week's temperatures in the sanctuary region. Is the monarch's over-wintering region in Mexico as warm as you expected it to be?
How to Respond to Today's Monarch Challenge Questions
1. Address an e-mail message to: email@example.com
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