NOVA traces the monarch butterfly's 2,000-mile migration to Mexico
from Canada and the Northeastern United States.
shows how a caterpillar changes into a butterfly.
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notes that it takes four generations to make the entire round
trip—one generation flies from Canada to Mexico, followed
by three more generations that complete the return trip and
year-long cycle.
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states that no one knows what triggers the exodus from Canada or
how the monarchs know how to navigate to Mexico.
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presents the threats monarchs face on their journey south,
including predators and bad weather.
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points out that the monarchs are able to make the long trip by
soaring on thermals and describes how thermals are formed.
provides maps that chart the migration's progress.
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visits the monarch's destinations, where the local Mazahua
people believe that the arriving butterflies carry the spirits
of their ancestors.
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explains that the monarchs rely on the Mexican mountain forest
because its canopy keeps the heat in and the rain out, and its
large trees retain and radiate heat the butterflies need to
survive during their overwintering.
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reports that while it is not fully understood how monarchs know
where to migrate, scientists have proposed theories that the
trip could be influenced by the sun's angle in relation to Earth
or that Earth's magnetic field provides a subtle orientation
guide.
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introduces Monarch Watch, started in 1992, which recruited
teachers and students to tag butterflies in the northeastern
United States.
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explains how monarchs that were moved from Kansas to Washington,
D.C., were able to reorient their course and head in the correct
direction to Mexico.
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reveals that illegal logging is endangering the Mexican forest
where the monarchs migrate.
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features the monarchs' arrival at their Mexican destination,
where they will overwinter for almost five months before
beginning the first leg of the journey back to Canada.
