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Monarch butterflies (''Danaus plexippus'') perform annual migrations across North America which have been called “one of the most spectacular natural phenomena in the world". Starting in September and October, eastern/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 five 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 at 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. == Range of the migration == 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. 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.〔(【引用サイトリンク】title=Monarch Migration Studies )〕 Fall-migrating monarchs are not the same ones that migrated northward approximately five months before. Instead the northern-migrating butterflies are at least five generations removed from overwintering sites. The eastern population migrates up to 4830 miles (7,778 km) to overwintering sites in Mexico. Other insects show migratory behavior but not nearly for as long distances. The exception would be the desert locust, ''Schistocerca gregaria'': it was reported once in 1950 that individual swarms were seen migrating from the Arabian peninsula over 5,000 km (3,105 miles) to the west coast of Africa in seven weeks. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Monarch butterfly migration」の詳細全文を読む スポンサード リンク
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