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Analyzing Data From a Fall Migration Roost
Contributed by Paul Viger, Campbell, Minnesota

During fall migration, some lucky people have thousands of monarchs pause in their yards at overnight roosts. Mr. Viger of Campbell, Minnesota, is one such person. Each day he counts the monarchs, tags them. He also records information about the wind and weather. Mr. Viger sent these pictures. How many tagged butterflies can you find in this roost?

The data below was collected during the fall 2001 season. The monarchs were present for almost 3 weeks and Mr. Viger noticed an interesting pattern. You can see it too if you look carefully at his data between August 27 and September 6.

  • Link to Mr. Viger’s Fall 2001 Monarch Roost Data
  • Make a graph to show the number of monarchs present each day between August 27 and September 6 (or print and analyze our graph above).
  • Look carefully at the wind direction he noted each day. (Write the wind direction for each date beside the data point on your graph.)
  • Then describe the pattern you see at Mr. Viger’s monarch roost between August 27 and September 6. What relationship do you see between wind and migration? Explain why you think monarchs might behave this way.
By the way says Mr. Viger, "The picture above of my two kids (Alex age 5 in 1991 and Emily age 3) has an interesting story. We tagged a few butterflies in the morning and I told the kids to bring their last ones to the house and I would get a picture. One of those butterflies was recovered in Mexico. It's neat to have a picture of a butterfly (I'm not sure which one) that made it to Mexico."

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