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Monarch Migration Update: March 15, 2000

Today's Report Includes:

Latest Migration Map and Data
The migration is off to an early start this spring! Sightings have already been reported from as far north as latitude 32 N --in Dallas and Tyler, TX and at the same latitude in Clinton, MS. These records are at least a full week earlier than those at the same locations last year.

Here is this week's migration map, and the Spring, 1999 map for comparison:

March 15, 2000

March 16, 1999

If you live in the Gulf States, please keep your eyes on the skies--and be ready to report migrating monarchs! Also watch your milkweed for signs of the first monarch eggs and larvae.

Field Notes from the Mexican Monarch Sanctuaries
Dr. Bill Calvert writes from Angangueo: "After all the reports we'd been hearing about butterflies arriving the earliest ever in the southern United States--and speculation about the unusually warm winter driving the butterflies north prematurely--we were all little apprehensive about what we'd find in the sanctuaries.

"Not withstanding all these negative reports and speculations, in 24 years of Mexican monarch watching, I'd never seen the colonies break apart substantially before the 20th of March--and indeed had often seen butterflies in substantial numbers here into early April. And when we arrived at El Rosario, our worries were totally dispelled. We were greeted by tree, after tree, after tree, fully laden with dark, clusters of butterflies. When the sun appeared, they filled the sky above and between the trees.

"Several of us had wandered to an area where the trees were heavily laden with butterflies which were especially close to the ground. We were staring and photographing when a sharp snapping sound rang out. A branch full of butterflies came down, spilling its colorful cargo all over the ground. The butterflies immediately began to rise by opening and closing their wings. Those on the upper side of the branch began to fly off in uniform motion and direction. Those on the bottom were trapped by the weight of the branch. Gingerly we lifted the branch and allowed them to escape. The branch was not small--perhaps 6-7 feet in length--so many thousands had come down with it. But within one half hour only a handful were left in the spot where the branch had fallen. So falling with a branch does not seem to harm many of them."

Butterflies Break a Branch
Imagine trees so full of butterflies that the branches actually bend--and can even break-- under their weight! It makes you wonder:

Challenge Question #16
"How much might that branch full of butterflies have weighed? To answer this question, assume the following:

  • the typical monarch butterfly weighs 400 mg in March
  • the average butterfly tree has 5 branches laden with butterflies
  • the answer from Challenge Question #6 below is correct (and is needed to answer this question!).

Give your answer in kilograms and in pounds. Also give name another object that weighs this amount, for comparison."

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

How Many Butterflies on a Tree?
Discussion of Challenge Question #6
Challenge Question #6 asked: "According to the averages Dr. Calvert provided in the Feb. 23rd update, how many monarchs might be clustered on a single tree in a monarch colony?"

Math students in Florida, Maine, Wisconsin and Texas all agreed: 32,500 monarchs! Congratulations to students at:
  • Hillcrest Elementary of Ellsworth, Wisconsin
  • Lincoln School of Vinalhaven, Maine
  • Citrus Elementary School of Vero Beach, Florida
  • Vidor Middle School in Vidor, Texas


How Many Millions of Monarchs?
Discussion of Challenge Questions #7 & #8
The students in Mrs. Sollock's 5th grade class in Vidor, Texas (lsollock@esc5.net) determined that 11,375,000 monarchs were clustered in the Sierra Chincua colony this January. If they could give 1 butterfly to each person, they could distribute butterflies to everyone in 3 states! They used the 1990 census population totals to calculate their answer:

"We combined 3 states' populations to total the 11,375,000. Try it! Combine the populations of Rhode Island, New Hampshire, and Michigan. (Hint: Round all numbers to the nearest hundred thousand.)"

The Cloud Effect
Discussion of Challenge Question #10

A cloud has just blocked the sun.
Photo by Dr. L. Brower

Dr. Calvert described a behavior of the colony called the "cloud effect". When a cloud blocks the sun, all the butterflies that were basking in the sun immediately push off into the air. He said this behavior is thought to serve an important purpose.

Challenge Question #10 asked, "What purpose do you think is served by the behavior known as the 'cloud effect'. That is, why do you think the butterflies suddenly fly into the air the moment the sun goes behind a cloud? What are they trying to do?"

Fifth Grade students Kaleigh, Caitlyn & Tasha Doelman of Scott Young Public School in Ontario, Canada replied:

"We think that the reason for the monarchs strange but incredible behavior is because when clouds gather or hide the sun it is usually a sign of rain. Since monarchs can't fly when their wings are wet they leave to the shelter of the trees. If they stay when it rains they would have to wait untill the water evaporated off their wings." (KevinC.Adams@TLDSB.on.ca)

Here's Dr. Calvert's explaination: "These butterflies have no way of knowing how long the cloud will last. If they were to remain in the exposed, basking positions without the sun, they soon may cool down and not be able to fly. This would compel them to stay there as long as the cloud persists--which could be overnight. By flying, they keep their body temperatures high enough to maintain mobility--either to return to basking position when the sun returns, or to go back under the canopy if clouds remain.

"What they are undoubtedly perceiving is a sudden lack of solar radiation and rapidly falling air temperatures. They are poikilotherms and cannot raise and maintain elevated internal temperatures without incoming radiation. They need high internal temperatures if they are to perform daily functions such as flying, crawling, mating, etc. At many locations and times during the winter season, nighttime radiational cooling takes surfaces exposed to the night sky down below freezing. If trapped there, the butterflies might freeze to death. Within their clusters, radiation and re-radiation trapped within vegetative mass of the forest and understory foliage keeps temperatures higher - as much as 5°C higher - than the exposed surfaces. The butterflies are clearly safer within the forest. This is where they try to go when radiation is blocked by a cloud for a long period."

Life in Sanctuary Region
A Walk in the Sanctuary With Guide Javier
One of the hopes for conservation of the monarch sanctuaries is through "ecotourism". ("Ecotourism" is a strategy for conservation that has developed over the past decade. Ecotourism refers to tourism in a natural area, and it usually implies that the local people can earn income from visiting tourists. This gives the people an economic incentive to protect natural land, rather than develop it for other economic uses.)

The people who own land in the monarch sanctuaries can often earn income as tour guides. Read today's interview with "Javier", a guide who leads tourists visiting the El Rosario sanctuary.

Then answer Challenge Question #17:

Challenge Question #17
"How does Javier feel about his work as a guide in the El Rosario Sanctuary? Do you think this example of ecotourim is working well? List the problems and successes Javier mentions in his interview."

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: jn-challenge-monarch@learner.org
2. In the Subject Line of your message write: Challenge Question #16 (or #17).
3. In the body of the EACH message, answer ONE of the questions above.

The Next Monarch Migration Update Will Be Posted on March 22, 2000.

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