Climate change may threaten North America’s iconic mass monarch butterfly migration.
Every fall, millions of monarchs (Danaus plexippus) travel thousands of kilometers over North America as they leave their breeding grounds in Canada and the United States for wintering grounds in a mountainous part of central Mexico. The butterflies make the trek back north over multiple generations when temperatures warm in the spring and summer months, following the growth of milkweed (Asclepias), their preferred food source.
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