Monarch Migration Update: March 22, 2000

Today's Report Includes:

Latest Migration Map and Data
 Link to This Week's Monarch Migration Data
The first monarch has already been sighted in Arkansas! Mrs. Brisco of Vera Kilpatrick Elementary wrote: "Spotted the first monarchs this spring about 4:00 P.M in a field just east of the city limits of Texarkana, AR (33.48N, -93.92 W). There were two monarchs - both heading almost due east. They appeared to be in good shape and were flying quite well."

How Far From Mexico Has the Migration Traveled?
Each week, plan to look at the latest map and find the forward edge of the migration.
• Chose a sighting that is the farthest from the sanctuaries. Using the latitude and longitude given in the migration data table, measure the monarch's distance from the sanctuaries. (The sanctuaries are located at 19 N, -100W.)
• First measure the distance on your map, using a ruler and the scale bar.

Challenge Question #18
"Assuming the monarch sighted in Arkansas (33.48N, -93.92 W) flew all the way from the Mexican sanctuaries (19 N, -100W), how far did that butterfly fly?"

Only Two Clusters Remain in Sierra Chincua Sanctuary
Meanwhile, back in the sanctuary region Eligio Garcia reports: "On the 16th of March there were only one or two clusters of monarchs in the Sierra Chincua sanctuary that had not yet left for migration. On the highway to Toluca, I saw many monarchs migrating toward the north. These butterflies came from the Cerro Pelon sanctuary that is very near Zitacuaro. The butterflies were heading more or less in the direction of the El Rosario sanctuary (which is to the north of Cerro Pelon)."
The Count is In!

Each week, you've received Eligo's measurements from one sanctuary, the Sierra Chincua. We've seen how the numbers of monarch trees varies over time, and how much the colony moves.

Once every winter, all of the colonies are measured. This is done in December, because during the coldest time of year the butterflies are clustered together most tightly. Like a snapshot in time, the annual winter measurements give scientists a chance to estimate the size of the entire over-wintering population. Here are this winter's measurements, courtesy of Sr. Roberto Solis the director of the Reserva Especial de la Biosphera Mariposa Monarca (REBMM):

How Many Millions of Monarchs in Mexico This Year?
Using Dr. Calvert's estimate of 13,000,000 monarchs per hectare, you can estimate the number of monarchs that over-wintered in Mexico this year. You can also compare the population size from one year to the next.

Challenge Question #19
"According to the data provided by Sr. Robero Solis, how many monarchs do you estimate were in Mexico during the past 6 years?
 1999/2000 1998/1999 1997/1998 1996/1997 1995/1996 1994/1995
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Watching the Wings for Clues
In our March 8 update, Challenge Question #13 asked, "How might a person in Texas be able to tell if the monarchs they see are from Mexico or are from the Texas over-wintering population?"

The fact is, we simply can't tell without killing the butterflies for chemical analysis. However, using a technique he learned from Dr. Karen Oberhauser and Dr. Bill Calvert, Texas teacher Harlen Aschen and his wife are conducting their own field research this year. They are exploring the many unanswered questions about migratory and over-wintering populations in the Gulf Coast region.

Because monarchs' wings become worn and faded over time, they can estimate how old the monarchs are. Age is a clue as to whether the butterflies might have recently emerged in Texas, or lived for many months and migrated from Mexico.

Here are 3 monarchs they captured in their backyard last week. Look carefully at each butterfly, and read and the descriptions the Aschens gave them. (See below.)

 #1 #2 #3

• Fade = 0: New, recently emerged.
• Fade = 2: No holes, no tattering, but beginning to have missing scales to cause fade.
• Fade = 4: Very faded, some tattering and holes. Orange beginning to turn gray, black just beginning to turn charcoal, but not yet transparent or "ghostly".

Texas Coast Monarchs Change Their Behavior
The Achens have also made this interesting observation after monarchs from Mexico began to be sighted in Texas:

3/19/00 Port Lavaca, Texas (28.53 N, -96.68 W)
"The monarchs for the past three weeks have been behaving differently. The ones we tagged and released between November and late February would be seen again for days, sometimes for weeks. Now, we tag and release and few are seen again. They might be sighted within a few hours again, but seldom the next day anymore. All movement has been from south to southwest heading north to northeast.

"We are beginning to notice 'loading' of eggs of the wild Asclepias viridis that we have been observing this week 7 miles west of Port Lavaca. We hope everyone to the north and northeast of us is on the lookout for tagged monarchs from Texas. They are also marked on both hind wings with a 'sharpie' (in blank ink)."

Coming Next Week: Weather and Migration
Get ready to explore how monarch migration is related to wind and weather. Beginning next week, Dr. Bill Calvert will help us look at weather maps and relate the conditions back to the week's migration.
How to Respond to Today's Monarch Challenge Questions|