FINAL Fall Migration News: November 15, 2012
Please Report
Your Sightings!
Report Your Sightings
We end our season with thanks to citizen scientists who make tracking fall migration possible. Now that the monarchs are reaching their destination, explore two key questions: Why do monarchs fly across the continent to reach this part of Mexico? How many monarchs survived the trip?

This Week's Update Includes:

Image of the Week
Monarch butterflies arriving in Mexico
They're Here!
Image: Estela Romero
News: The Monarchs Are Arriving!
After two weeks of cold and rain—and very few monarchs—Estela was astonished to discover thousands of butterflies at El Rosario Sanctuary on Monday:

"Let me say that, after several very frustrating days, indeed the MONARCHS HAVE ARRIVED TO THEIR WINTER HOMELAND IN ANGANGUEO!!!," she exclaimed in this week's report.

Last Year's Arrival
There were 60 butterfly trees counted at El Rosario last November 1st according to this press release. See photos and tree counts made last year at this time (in Spanish).

December Counts
Every December, scientists visit the 12 traditional wintering sites and measure the surface area the butterfly colonies cover. This chart shows the data scientists have collected for 18 years. Results will be released in February, 2013.

Population Predictions?
The measurements made in Mexico are the most reliable estimate we have of the size of eastern North America's monarch population. Dr. Lincoln Brower predicts this winter's population will be the smallest ever recorded. When the results are released in February, 2013 we can assess:

  • How productive was the breeding season?
  • How many monarchs survived fall migration?

Thank You!
It's time to say thank you, citizen scientists one and all, for helping to track the monarch's fall migration. Your photos and comments told the story, and we are grateful and enriched by your participation. Please join us again on February 7, 2013. We'll begin with preparations for spring migration and celebrating the monarchs' return!

Special Delivery
Image: Estela Romero

Press Release

Last Year
Image: Felipe Martinez Meza


Population Estimate: Monarch Butterfly Overwintering RegionDecember Counts

Winter in Mexico: Month-by-month Highlights
November   December
Monarch Butterflies arriving in Mexico   Scientists visit the 12 wintering sites and measure the surface area the colonies cover.
Monarchs Arrive
Throughout the month, monarchs continue to arrive from the north and settle in at the 12 traditional wintering sites.
  Scientists Count
Scientists visit the 12 wintering sites and measure the surface area the colonies cover. Results will be released in February, 2013.
January   February
Monarch Butterflies wintering in Mexico   Monarch Butterflies wintering in Mexico
Surviving Cold
Watch the weather! At this coldest time of year, monarchs are at the greatest risk of mortality from deadly winter storms.
  Preparing to Migrate
Monarchs that survive four winter months will mate and begin the journey north in March. Join us for weekly updates on Feb. 7, 2013.
Slideshow: Why is this place so special for monarchs?
Hundreds of millions of monarchs migrate to Mexico to spend the winter in an astonishingly small region. The butterflies gather on a dozen mountaintops in a region only 73 miles wide. What conditions make the habitat in this region ideal for monarch survival? This week, learn about the unique microclimate of the monarch overwintering region.

Slideshow: Why is this place so special for monarch butterflies?

The Migration: Maps and Journal Page
Continue to report your sightings. Document where monarchs found this winter.
Winter Monarchs?
When you see a monarch, we want to know about it.
Monarch Butterfly Migration Map: All Sightings, Fall 2012 Monarch Butterfly Migration Map: Peak Migration, Fall 2012 Journal

All Sightings
(map | animation | sightings)
Peak Migration
(map | animation | sightings)
This is the FINAL Fall Monarch Migration Update. We're back Feb. 7, 2013!