Monarch Migration Update: September 20, 2012
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It was a week of peak migration along the Atlantic coast. "An endless number heading south," said one observer. With up to 3,000 miles to fly, will these monarchs make it to Mexico? Tagging data reveal their chances.

This Week's Update Includes:


Image of the Week
Flight of the Butterflies

Flight of the Butterflies

News: Streaming Along the Atlantic
From Maine to Maryland, people reported a procession of monarchs on their way to Mexico. Migration was particularly strong at sites along the coast:

"Thousands at an oceanside park in Kittery Point, Maine. It was like being in a dream sequence. Nature at its most amazing!" 9/16/12 Kittery, ME

"On a whale watch trip monarchs fluttered around us even when we were 10 miles off shore..."9/16/12 Rye, NH

"There was a strong northwest wind and the constant flow of monarchs was amazing. In 4 hours approximately 3000 monarchs gracefully flew over the ocean, the beach, the roads and the sand dunes." 9/16/12 Gilgo Beach, NY

"While walking along the surfline, two monarchs flew past us, coming in east off the Atlantic ocean! Both immediately dropped, exhausted, onto the damp sand and proceeded to 'puddle' for moisture." 9/10/12 Ocean City, MD

Comparatively Quiet
Have you noticed? This season's peak reports have been concentrated along the Atlantic Ocean, as the peak migration map shows. Monarchs appear to be relatively scarce in the central flyway of the Midwest, the region where monarchs are usually most numerous.

  • Is the monarch population truly as small as it seems?

In December, scientists in Mexico will make their annual measurements. We will see how this year's monarch numbers compare to those in years past.


Migrating From Maine
Migrating From Maine
Image: Donna Morton
Peak Monarch Migration in Maine
Peak Migration
Image: Lisa Munoz
Monarch Butterfly Roost on Long Island, New York
Migration Stopver
Image: Deborah Klein
Comparing Flyways: Tagging Data Reveal Chances
Two Flyways
The migration map shows the two main flyways in eastern North America. Monarchs traveling to Mexico from the eastern flyway have a longer distance to travel. Do eastern monarchs have a reduced chance of making it to Mexico?

Tagging Data Reveal Chances
Every fall thousands of people tag butterflies for the Monarch Watch program. Tagging data let us compare the likelihood of reaching Mexico from different regions.

Overall, roughly 1 in 100 monarchs tagged in eastern North America is recovered in Mexico. Recovery rates vary depending upon where the butterflies were tagged. As shown on this graphic, monarchs tagged on the eastern coasts have an extremely low recovery rate.

Challenges for Eastern Flyway Monarchs
Three factors make migration from the eastern flyway more difficult than from the central flyway:

  1. Longer distances
  2. Westerly winds
  3. Atlantic Ocean and Gulf of Mexico
Monarch Butterfly Migration Flyways Map
Two Flyways


Recovery Rates of Tagged Monarch Butterflies
Tagging Data
The Migration: Maps and Journal Page
Watch for monarchs that are flying in directional flight, resting at overnight roosts, or refueling at flowers in fields, gardens, or roadsides.
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Monarch Butterfly Migration Map: All Sightings, Fall 2012 Monarch Butterfly Migration Map: Peak Migration, Fall 2012 Journal Page
All Sightings
(map | animation | sightings)
Peak Migration
(map | animation | sightings)
The next migration update will be posted on September 27, 2012.