Butterfly Migration
JB: This is Earth and Sky, on monarch butterfly migration.
DB: It’s been known for years that the butterflies fly south each year beginning in late August. Around that time, the butterflies can be seen landing in trees around dusk. People have observed these overnight clusters from the midwest to the Atlantic coast – from Maine to Texas. But the butterflies’ final destination was a mystery until about 30 years ago.
JB: In the 1950s, researchers, school teachers and amateurs began tagging monarchs. Tens of thousands of monarchs were released with numbered labels on a front wing that said, “send back to the University of Toronto Zoology.” By plotting the points of release and recapture, scientists determined the butterflies were flying in a southwesterly direction – into Texas and toward Mexico.
DB: An overwintering site’s exact location was finally discovered in January 1975. A major clue came from an American salesman’s drive through a hail storm west of Mexico City – when monarch butterflies were pelted from the sky. An intense search revealed a small area of forest high in the mountains – where fir trees were covered with millions of butterflies.
JB: Find out how you can help preserve monarch butterflies’ sites – come to today’s show at earthsky.org. Thanks today to the National Fish and Wildlife Foundation – and to the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individual was interviewed for today’s show. Our thanks to:
Lincoln P. Brower
Research Professor of Biology
Sweet Briar College Lynchburg, VA
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For more information on monarch butterflies:
Monarch butterfly sanctuary foundation (Learner.org)
Monarch butterflies (Nature.org)
“”Habitat Loss in Mexico Threatens the Monarch Butterfly Winter Migration: An Interview with Lincoln Brower. Environmental Review Newsletter Volume One Number Six, June 1994
Author’s Notes:
In California, monarch butterflies migrate to the Monterey Peninsula to spend the winter. The following spring they fly eastward to breed in the Sierras. Their great grandchildren come back to Monterey the next fall This proves that the migration is a genetically inherited pattern of behavior that enables them to find their way back to exactly the same over–wintering sites in Mexico– but nobody knows how they navigate when they migrate.
