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Monarch Butterfly Migration Update: May 23, 2002

Today's Report Includes:

News From the Migration Trail

This Year

Last Year


  • Link to Data: Link to This Week's Migration Data
  • Migration sightings picked up again this week, but only slightly. This week's 25 sightings compare to 75 sightings during the same week last year.
  • This spring's migration map now shows the most dramatic contrast from last year's. Notice the differences in both the abundance of monarchs and the advance of the migration.
  • Curiously, 40% of this week's reports were from Iowa. There the migration has now advanced to about 43 North-some 60 miles ahead of its position last week.
  • In the East, monarchs have now been reported from as far as 41 North. Again this is only about 60 miles ahead of its position last week.
  • We're still waiting for the first report from Canada. Last year's first was May 2nd, now three weeks ahead of today's date.
  • Most everyone noted fresh wings on the butterflies they saw. Now that it's late May, we can safely assume all sightings were of the new spring generation. These "first generation" sightings are marked on the migration map with a black dot in the center. Thus, the map shows how far the generation from Mexico advanced this spring.

Cool Weather Halts Advance into Northern Regions
It was the unusually cool weather last week that essentially stalled the northward advance of the migration. As the strong high pressure system responsible moves eastward, south winds and warmer temperatures will follow. (See maps below.) How far north do you predict the monarchs will have been sighted by next week at this time?

Last Week's Temperatures
(Departure from Normal)

High Pressure Moves East

South Winds Follow

Monarch Generations: Which Generation Will Go to Mexico in the Fall?
Spring is the beginning of the monarch's breeding season. The monarchs that migrated north from Mexico in March are of a very unusual generation. They do not breed until they are 8-9 months old--and not until after they have survived two migrations and a long winter in between. In contrast, during the summer breeding season, monarchs live for only 2-5 weeks! Several generations live and die each summer, and it's the final generation that migrates to Mexico in the fall.

Using the worksheet below, you can figure out which generation migrates to Mexico. Here is the question: Of the monarchs that spent last winter in Mexico, do you think this fall's migratory generation will be:

  • their children?
  • their grandchildren?
  • their great-grandchildren?
  • their great-great-grandchildren?
  • their great-great-great-grandchildren?
  • their great-great-great-great-grandchildren?

&you have the idea, now see if you can calculate the answer!

Stay Tuned: The Monarch Migration Continues!
Other Journey North migrations have come to an end, but we'll continue to track the monarchs until they ve expanded across their entire breeding range. This normally takes until mid-June, but may take more time this year because the population is so low.

Please Help: YOUR Monarch Sightings Are Important
This is an ESPECIALLY important year to be watching for monarchs. Even after monarchs have been reported from your state or province, we want to hear from YOU when you see YOUR first! And, if you don t see your first monarch until later in the summer, please report it then. The number of sightings reported reflects monarch abundance, so your observations will continue to be important.



Journey North
Year End Evaluation
Please share your thoughts

The Next Monarch Migration Update Will Be Posted on May 30, 2002

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