Abstract
As a result of alar tagging migrating specimens of the monarch butterfly (Danaus p. plexippus L.) in North America over a period of 25 years, it was possible to plot the migration routes establishing two large overwintering colonies, one located in California and the other in mountains of the Sierra Madré Occidentale in Mexico. Photographs of the two overwintering populations are presented together with release–recapture lines showing the direction of migration from breeding areas to the two overwintering sites. Data, presented for the first time, show the migration routes of the Western population from the breeding areas in the mountains and west of the mountains to California.

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