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Monarch Migration Update: April 20, 1999

Today's Report Includes:

Cold Front Stops Migration in its Tracks
The monarch migration came to a screeching halt last week. Notice that only 2 sightings have been reported since last Tuesday, April 13th:

On Wednesday, the 14th, a strong cold front began its sweep across the U.S. and stopped the migration in its tracks. Look at these weather maps which show north winds of up to 40 mph in NE and KS, for example:

Link to Additional UNISYS Weather Maps for April

April 14 April 15 April 16

The same front reached into Texas, where Harlan Aschen made a fascinating observation. Two weeks earlier, he had tagged individual butterflies in his garden: "The male monarchs that had been visiting (every day) since the end of March have not been seen since the cold front came in Wednesday, " he said on Sunday. "The front brought record lows for this part of Texas and came in with a strong northwest wind." This came as quite a surprise, considering the assumption when he tagged them: "We really want to find out the destination of these coastal monarchs. Hopefully to see which way they go when they leave the coast north and northeastward." Be sure to visit the Aschen's Website where you'll even find pictures of these now-famous tagged monarchs.

How Far North Do Mexican Monarchs Travel?
Your migration map now shows a very clear picture of how far north the monarchs from Mexico have traveled so far. Notice that the leading edge of the migration has now reached about 40 N all across the monarch's range. Exactly how far might these individuals have traveled? Last week we asked Challenge Question #27: "Assuming it flew from Mexico, how many miles did the monarch now in Maryland fly?"

Ms. Baily's students in Vero Beach, FL figured it this way: "We used this Distance Calculator link to help us find the distance from Mexico to Maryland. We found out that as the crow flies, the distance from Mexico City to Maryland is 1960 miles or 3084 km. I guess we should say that's 'As the butterfly files'."
How Long Have These Monarchs Been Alive?
Last week we looked at development time for monarchs that live during the breeding season. In contrast, these migratory butterflies live a long, long time. How long have they been alive, anyway?

Challenge Question #29
"Assuming a butterfly emerged as an adult on August 20 in Maine--and another in Texas on October 20--as of April 20, how long has each butterfly lived?

(To respond to today's questions, please follow the instructions below.)

Risks of Arriving Early
Discussion of Challenge Question #26

"Can you think of 3 reasons why it might be risky for monarchs to travel so far north this early in the spring?" we asked.

Students in Illinois, where early monarchs have been reported, can look outside and tell why monarch habitat is not yet ready:

"We have not seen many milkweed plants growing in our community. Therefore the monarchs food source may be limited. The female monarchs do not have many plants to lay their eggs." Said students in Ms. Probst's class at Grove Elementary. They added, "Monarchs are at risk for traveling too far north this spring because in Illinois we have been having night time temperatures dip down into the 30's."

Even though they're far off in Florida, Ms. Bailey's students can imagine another risk:

"The monarchs need to feed on nectar from flowers that may not be blooming yet." (

More Monarchs Still Coming from Mexico
By the way, two separate observers in Monterrey, Mexico (25.67 N, -100.32 W) reported a noteworthy migration on April 10, indicating that more monarchs are still moving through Mexico--and on their way north. Bill Calvert commented: "This doesn't seen too late for monarchs going north. We saw them in numbers on 25 March at the over-wintering colonies. So that's 16 days later in Monterrrey. Monterrey is about 350 miles north, so they travelled 350 miles in 16 days. This doesn't seem unreasonable to me!"

Challenge Question #30
"If it's reasonable for monarchs to travel 350 miles in 16 days, how many miles per day is that?"

(To respond to today's questions, please follow the instructions below.)

Monarchs Now in 17 States
Discussion of Challenge Question #25

"In how many NEW states were monarchs seen during the past week? What is the total number of states in which the monarchs from Mexico have now arrived?"

This was a difficult question, because it required looking back at all the data posted. Here are our records. You may want to continue to keep track of the number of states--and soon Canadian Provinces--the monarchs have reached.

As of April 13 the monarch migration had reached:
  • 8 new states and they are: MO, GA, IL, KS, AL, NC, MD, NM
  • 15 states in total as of April 13, including: TX, LA, FL, AR, MS, TN, OK, MO, GA, IL, KS, AL, NC, MD, NM. (The monarchs reported in California are not from the Mexican over-wintering sites, so were not included in our count.)
  • And as of this week's report, monarchs are now in 17 states. Both NE and NJ were new to the list this week.

Weather and Migration: Three-Week Summary
During the first 2 weeks of April, prevailing south winds blew consistently in Texas and the Plains States, delivering monarchs into 15 states by April 13th. Between April 6 and April 13 alone, the migration reached 8 new states. With the arrival of the cold front on April 14, notice how little the migration progressed during the past week:

As of April 6

As of April 13

As of April 20

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 # 29 (or Challenge Question #30).
3. In the body of EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on April 27, 1999.

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