When do monarchs migrate?

In autumn, these regal butterflies travel up to 2,000 miles over 2 months. Those from east of the Rocky Mountains head to a 30-by-50-mile patch of forest in the mountains of south-central Mexico, and those west of the Rockies winter in southern California. The only exception is the nonmigratory population in southern Florida. There, monarchs continue to breed and produce caterpillars year-round.