Journey North Monarch Butterfly Spring 2006

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?
Today's Report Includes: Field Notes from Mexico from Dr. Bill Calvert How Many Monarchs are in Mexico? Here’s the News! Measuring Twice Makes a Mystery How Are Monarch Colonies Measured? Imagine the Scientists' Job! Give it a Try! Challenge Question #5 Now Take a Look at the Scientists' Methods How Many Variables Can YOU Identify? Pictures and Descriptions Hold Clues Challenge Question #6 Ask the Expert Opens Today!
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.
	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? >>
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.
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.	Monarchs cover the trees like a luxurious carpet, as seen from above. Copyright Dr. Lincoln Brower, Sweet Briar College
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.
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
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? The Scientists' Methods
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? How Many Variables Can YOU Identify? More Pictures and Descriptions Hold Clues
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.
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): Submit your questions on the Web (beginning 3 pm today EST)
The Next Monarch Migration Update Will Be Posted on March 10, 2006