The migration has entered Mexico, but it has been a quiet passage so far. Meanwhile, monarchs are moving along the Gulf coast in unusally large numbers, and should funnel their way into Texas next. Will cold temperatures across the north stop the remaining monarchs in their tracks? This week, explore the relationship between flight temperature.

This Week's Update Includes:

• News: Crossing into Mexico!
• Slideshow: Too Cold to Fly?
• Hola Desde Mexico: Hello from Mexico
• The Migration: Maps and Journal Page

News: Crossing into Mexico!

Large numbers of monarchs have been crossing the border into Mexico for over a week, according to our observers. As soon as the butterflies cross the Rio Grande River they are in Mexico:

"The monarchs are uniting three countries when they cross the Rio Grande," wrote Leticia Avendaño who lives on the Mexican side in Ciudad Acuña, Coahuila.

Texas Central Flyway
Carol Cullar lives on the U.S.–Mexico border in Eagle Pass, Texas. She sent an update on Thursday, along with pictures of the landscape the monarchs are crossing now, called the chaparral.

"Monarchs flying through this vast region have been very lazy about migrating. We've had no powerful 'northers' sweeping them out the door! They 'hung up' between Sonora and the Hill Country in Central Texas for at least a week before they finally began to mosey on down this way," said Carol.

Northern Mexico
Señora Rocío Treviño coordinates Mexico's migration-tracking program called Correo Real. Until today, the migration has been taking place almost imperceptibly. However, she came inside this morning to send this news:

October 22: Saltillo, Coahuila
"At this moment large numbers of monarchs are passing, and I am getting calls from across the city. I counted 21 per minute this morning from 9:30-10:00. Miren al cielo! (Look to the sky!)," said Rocio.

At the same time, students nearby at Escuela Secundaria Technica 73 reported:

October 22: Saltillo, Coahuila
"Today my students and I watched more than 250 monarch flying form west to east at 9:10 am. We are so excited about watching the monarchs passing by our school," exclaimed teacher Melida Cortes.

Cold Temperatures Across the North
Frigid temperatures are moving across the monarch's northern breeding range now. Because monarchs are cold-blooded, they must leave the north before they're trapped by the cold. This map shows how quickly temperatures drop as the fall season progresses.

Will cold temperatures across the north stop the remaining monarchs in their tracks? This week, explore the relationship between flight temperature.

"It has only been a few days since the miners of Chile were rescued. Because Angangueo was a mining town for many years, we are all very impressed with what happened in Chile," wrote Estela Romero.

Jaime and Yahir interviewed their grandfather who was a minining engineer for 45 years. "No monarchs yet! " added Estela Romero on Tuesday.

• Hello From Angangueo!
• Hola Desde Angangueo!