Final Migration Update: November 4, 2008

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This week's highlights

Latest News: Now Arriving at the Sanctuaries!

Estela Romero reports that large numbers of monarchs have now reached Mexico's overwintering region. By November 2nd, the tops of fifteen trees at the El Rosario sanctuary were covered with monarchs. That day, there were no more monarchs resting at El Cerrito, the site near her hometown of Angangueo where the butterflies first appear. Instead, hundreds were passing by and flying the last mile toward El Rosario. "The Monarch season is really starting now," she said.

How will it look as the monarchs arrive over the next few weeks? Here are photos and links to explore!

  • Mass Arrival at the Sanctuaries: As thousands upon thousands of butterflies reached the El Rosairo sanctuary one November, Dr. Carlos Galindo-Leal snapped the spectacular images at this link. How many monarchs did he see in this single patch of sky? Think about the question, then find a way to estimate.
  • Watching the Arrival in Mexico: "Monarchs were everywhere: flying past windows and over rooftops, past donkeys carrying loads of wood, past children dressed in red school uniforms, past men wearing the cowboy hats of Michoacan, past chickens in people's yards and houses painted with vivid colors. Against this backdrop of Mexican life were the same monarchs, so familiar in my garden at home, but now in an entirely different place."

Maria Estela Romero
reports from Angangueo

Monarchs will appear by the thousands in the sky above Angangueo as they arrive in November. (2005 photo)

Predict: How Large Will This Winter's Population Be?

How many monarchs will make it to Mexico? How large will this year's overwintering population be?

Scientists will measure the size of this year's overwintering population in December. They have been making such measurements every winter since 1994 as show on the graph.

The population naturally fluctuates (goes up and down). However, scientists need to learn how widely it can fluctuate and still be healthy. During last summer's breeding season, monarch expert Dr. Chip Taylor projected this winter's population will be lower than last year's measurement of 4.61 hectares. Based on what we've seen during this fall's migration, how large do you predict this winter's population will be?

Here are some observations to consider:

  • Summer breeding: People across the breeding range said monarchs were scarce this summer compared to past years.
  • Fall migration: Only 13 roosts were reported in August compared to 68 in 2007 and 33 in 2006. At the end of the season, a total of 135 roosts had been reported this year compared to 270 in 2007 and 170 in 2006.
  • Fall migration: This year's average migration rate at the Monarch Monitoring Project in New Jersey was 30 monarchs per hour, the 5th lowest count in the study's 16 years. For perspective, in 2007 there were 80 per hour and 202 per hour in 2006.

Do you think there will be any correlation between these observations and the size of this winter's population? Look at the population chart and make your own prediction. Watch for the actual measurements when Journey North begins in February!

How Many Monarchs in Mexico This Year?

The monarch population is measured each winter in Mexico. This graph shows data from the past 14 years. How do you predict this winter's population will compare to those in past years?

Student Handout

The Migration: Maps, Data and Questions

Fall Roosts


PEAK Migration


ALL Monarch
Migration Sightings


Distribution Map >>

About these maps >>


Make your own map >>

This Week's Questions >>

Focus: Monarchs and Mexican Traditions

In November, when the monarchs return to their sanctuaries, the people of Mexico are celebrating Dia de los Muertos (Day of the Dead). Estela Romero explains the connection to monarchs in this slideshow: "Our pre-Hispanic ancestors believed, and we continue to believe, that the souls of our dead relatives come to stay overnight with the whole family on the night of the 2nd of November. Our ancestors who settled in the state of Michoacán believed that the monarch butterflies arriving were the souls of our relatives arriving to their hometowns."

  • The Day of the Dead at Our School in Angangueo (English)
  • The Day of the Dead at Our School in Angangueo (Spanish)

The Day of the Dead
at Our School in Angangueo


Other News: Citizen Science Centerpiece at Tri-national Monarch Workshop

Monarch butterflies migrate across Canada, the United States and Mexico. People from the three countries met last week in northern Mexico for a monarch butterfly workshop, led by biologist Dr. Karen Oberhauser. The goal of the workshop was to involve more everyday people in monarch monitoring.

“We would not know what we know about monarchs without citizen science,” she emphasized. “Citizen science is necessary to our understanding of monarchs.”

The overarching challenge for scientists is to understand how monarchs are faring in North America, and to understand the threats the butterflies face. Help from citizen scientists is the centerpiece of the scientists' strategy for meeting this challenge.

Teams from Mexico, the United States and Canada attended the monarch workshop in Saltillo, Coahuila, Mexico. >>
Photo courtesy of Don Davis
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