Monarch
Butterfly Migration Update: March 3, 2006 |
How
many monarchs are in Mexico this year? The news is in! Scientists
say this year’s population is almost three times larger than
last year’s. Like a snapshot in time, they estimate the size
of the entire overwintering population each winter. But how do the
scientists make these estimates? Look carefully at their methods.
Then try your skill at this challenging task!Also,
Dr. Bill Calvert reports from Mexico that the colonies have begun
to break up. Why does this happen every year at this time? |
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Today's
Report Includes:
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Field
Notes from Mexico from Dr. Bill Calvert |
"Found
tag!" begins Dr. Calvert. "I wonder where she is from..."
Perhaps he found a butterfly that YOU tagged last fall?
The
butterflies are moving! The colonies split and move every year at
this time--why? "Basically the entire mountainside is as dry
as a bone and the butterflies are forced out of the colonies down
to open sources of water to drink, "explains Dr. Calvert. |
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You can read
and hear Dr. Calvert's news and observations. |
How
Many Monarchs are in Mexico? Here’s the
News! |
All
of the known colonies in Mexico are measured once
each winter. Like
a snapshot in time, these annual winter measurements give scientists
a chance to estimate the size of the entire overwintering population.
This
year’s official estimate: The butterflies cover
5.92 hectares. (One hectare equals 2.47 acres.)
This
graph shows each winter's population estimate for the past 11 years.
This year’s population is nearly three times greater than
last year’s. (Note, however, that last year’s population
was the lowest in a decade.) |
What comparisons can you make between this winter's
population and those in the past 11 years? >>
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Special
thanks to Carlos Galindo and Eduardo Rendon of WWF-Mexico and
their colleagues at the Reserva de la Biosphera Mariposa Monarca
(REBMM). Link to original
report.
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Measuring
Twice Make a Mystery |
Scientists Carlos Galindo, Eduardo Rendon, and their team visited
all of the colonies twice. They repeated their measurements two
separate times. All visits were made in December, and they were
two weeks apart. The scientists' results raised some intriguing
questions. Here's what they found: Based on the first round of measurements
the total coverage was 7.15 hectares--substantially higher than
the 5.92 hectare official total they obtained on the second round.
According to the scientists' observations, there were no storms
or other reasons for mortality between the two visits.
- What
could account for such a big difference in just two weeks? Think
about this question as you read today's update.
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Monarchs
cover the trees like a luxurious carpet, as seen from above.
Copyright
Dr. Lincoln Brower, Sweet Briar College
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How
Are Monarch Colonies Measured?
Imagine the Scientists' Job! |
Too
many butterflies to count! |
It's
a daunting task to estimate the size of the monarch's winter colonies!
But because it's so important to know the size of the monarch population,
scientists have developed a method for estimating their size. It is
NOT EASY, as you are about to see. In real life, the butterflies,
the forest, the weather, and even the scientists are variable. Keep
in mind: When we hear numbers, we tend to take them as fact.
But nobody really knows how many butterflies there are! We can only
estimate. |
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Give
it a Try! |
How
many butterfly trees do you count? |
Before
we look more closely at the scientists' methods, walk
into a sanctuary, take a look, and try it yourself.
- Challenge
Question #5
"How many butterfly trees did you count in the colony pictured
here? Describe the challenges you had. (For extra credit, name
a few variables the scientists must control when estimating the
size of the monarch population. Consider the butterflies, the
forest, the weather, and even the scientists.)"
As
you work, record the challenges you notice, the questions you have,
and the decisions you make to reach your final count. |
(Click
image to enlarge.)
Copyright
Dr. Lincoln Brower, Sweet Briar College
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Now
Take a Look at the Scientists' Methods |
Mexican
Scientist Eduardo Rendon |
Are
you ready now to see how the scientists work? Read the detailed
description of the steps they take. Did you find a need to control
the same variables they do?
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How
Many Variables Can YOU Identify? Pictures
and Descriptions Hold Clues |
Look
at the pictures and information at the link below. Keep the scientists'
methods in mind. Use the worksheet to record the
variables you identify that are hard or impossible to control. How
might each variable affect the accuracy of the results?
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Challenge
Question #6 |
Send
us your answers! |
Challenge
Question #6
"This year’s monarch population is estimated to cover
5.9 hectares. How many football fields would all of this year’s
butterfly trees cover?"
- To
respond to these Challenge Questions, please follow these instructions.
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Ask
the Expert Opens Today! |
American
Scientist Karen Oberhauser |
Once
again this year, monarch biologist Dr. Karen Oberhauser has volunteered
to respond to students' questions. We are thrilled to offer this
opportunity to you! We will accept questions for the next two weeks
(March 3-24, 2006):
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The
Next Monarch Migration Update Will Be Posted on March 10, 2006 |