November 6, 2009
This news just in: The monarchs arrived in large numbers yesterday at Mexico's winter sanctuary region.

The news was announced by biologist Eduardo Rendon, who heads World Wildlife Fund-Mexico's Monarch Butterfly Program.

"Today, all of the roads that lead to the Monarch Reserve are full of butterflies," he reported yesterday. Evidently the monarchs began to arrive on Sunday and Monday, when the first trees containing clusters were found in the Sierra Chincua and El Rosario sanctuaries. Yesterday was the first day with such a clear, massive arrival.

You can read Eduardo Rendon's announcement below in Spanish. Meanwhile, picture millions of monarchs flying across the finish line as they complete their long migration. Congratulations, monarchs! We'll be back next week with our final migration update of the season.

Estimados todos,
El domingo y lunes inició el la llegada de mariposas a los santuarios de hibernación. Los primeros árboles con mariposas fueron encontrados en la Sierra Chincua y en Sierra Campanario. Mientras que solo fueron vistas mariposas en el Cerro Pelón.

Hoy por todas las carreteras que confluyen a la Reserva están llegando las mariposas. Mi impresión es que se trata del primer día con esta cantidad de mariposas llegando. Acerca del tiempo de llegada, habrá que decir y considerar que fue con 10 días de retraso.

Gracias,
Eduardo Rendón Salinas
Coordinador de Programa Mariposa Monarca
World Wildlife Fund (WWF) México

Eduardo Rendon Salinas
announced the news.

The Arrival
as witnessed by Biologist Felipe Martinez Meza, Director of the Monarch Reserve.

The finish line!

Mexico's Monarch Butterfly Overwintering Region

Millions and millions of monarchs migrating to Mexico will spend the winter--together--in an astonishingly small region. The butterflies gather and form tight, clustered colonies in the region region that's only 73 miles wide.

What conditions make the habitat in this region ideal for monarch survival? In this week's slideshow, find out what scientists are learning about the unique microclimate of the monarch overwintering region.

• Slideshow: Why is this place so special for monarchs?

Why is this place so special for monarchs?