Monarch butterfly migration

Monarch butterflies (Danaus plexippus) perform annual migrations across North America which have been called "one of the most spectacular natural phenomena in the world". The subspecies D. plexippus plexippus is the migratory one. Other subspecies perform minor migrations or none at all.

Starting in September and October, eastern and northeastern populations migrate from southern Canada and the United States to overwintering sites in central Mexico where they arrive around November. They start the return trip in March, arriving around July. No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least four generations are involved in the annual cycle.

Similarly, the western populations migrate annually between regions west of the Rocky Mountains including northern Canada and overwintering sites on the coast of California.

Monarchs also perform small distance migrations in Australia and New Zealand. There are also some populations, for instance in Florida and the Caribbean, that do not migrate, as well as the subspecies distributed in the Caribbean, Central America and northern south America. Recently discovered overwintering sites have been identified in Arizona and northern Florida.

The western population overwinters in various coastal sites in central and southern California, United States, notably in Pacific Grove, Santa Cruz, and Grover Beach. Western monarchs also overwinter in Baja, California's central valley, and the Sierra Nevada foothills.

Not all monarchs migrate. Migrating populations and non-migrating populations coexist in many areas. Monarchs are year-round residents in Florida and monarchs migrate to Florida and Gulf coast areas, and can often continue to breed and survive the winter. The monarch population in Florida may be a result from migratory butterflies that do not to migrate north in the spring. These locations provide access to nectar plants. If there is a hard frost in these areas they do not survive. Asclepias curassavica, an introduced annual ornamental, provides larval food if native species are unavailable, although because of the risks to monarchs from the spread of the parasite, OE, this plant is not recommended for planting. Year-round breeding of resident monarch populations exist in the Caribbean, and in Mexico as far south as the Yucatán peninsula. Surprisingly, monarchs do not migrate over most of their global range. Tagging records demonstrate that the eastern and western populations are not entirely separate. Arizona butterflies have been captured at overwintering sites in both California and Michoacan, Mexico. In some instances monarchs from Arizona and New Mexico were found overwintering in California and in Mexico.

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Wikipedia