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from the Migration Trail
days after a cold front pushed spectacular numbers of monarchs
across west Texas, they cruised into northern Mexico, 200 miles
to the south. But this time, people saw "miles y miles
de mariposas monarcas" and said a "frente frio"
FIN LLEGARON!" they said.
"At last they are arriving!"
thanks to Rocío Treviño of Correo Real for forwarding
these spectacular observations from northern Mexico this week!
observations(in Spanish) >>
entering Mexico must go through customs. Monarchs can fly between
the countries without stopping!
Rio Grande River is the Border
Texas, the Rio Grande River marks the border between the U.S.
and Mexico. Above: As seen between Del Rio, Texas, and
the international bridge between Del Rio and Acuña, this
line on this sign declares the exact border between the United
States of Mexico and America.
Migration Through Mexico
map below shows the route the monarchs probably take as they cross
Mexico. It is based on observations made by biologist Dr. Bill
Calvert--and many others--during fall migration. The direction
the monarchs travel is "delightfully confusing!" says
Dr. Calvert. The map illustrates a mystery of monarch navigation.
a look: The monarch's winter home is directly south
of the region in Texas (centered on Del Rio) where most monarchs
cross the border into Mexico. However, the monarchs don't travel
straight south as they cross Mexico. Study the map and notice
the way the monarchs travel instead. Compare the line of longitude
-100 West to the path of the migration.
about this question:
Why don't the monarchs travel straight south as they cross
to see larger
read Dr. Calvert's description >>
Next Monarch Butterfly Migration Update will be posted on November 3,
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