Some seabirds that nest in the southern oceans go north for their winter. Sooty shearwaters fly from their nesting areas in the Falklands and Tierra del Fuego to Arctic waters near Norway and back again, over 17,000 miles in the Atlantic (round trip); in the Pacific, they fly even farther, from near New Zealand to the Gulf of Alaska. Short-tailed shearwaters fly still farther: they breed near Tasmania and migrate to the North Pacific; some even go through the Bering Strait to the Arctic Ocean.<\/p>\n\t\t\t\t
All of these critters are relatively long-lived, with lifespans measured in years or decades, and may make those journeys many times in their lifetimes. And in most cases, they can feed along the way.<\/p>\n\t\t\t\t
There are long-distance migrants among the insects, too, but they are relatively short-lived, with adult lifespans measured in days or weeks, and they do it differently. A single individual does not make the round-trip journey; instead, they breed along the way and the next generations take over the route.<\/p>\n\t\t\t\t
The best-known example in North America is the monarch butterfly. Monarchs that are born and raised in the eastern U.S. and southern Canada migrate to special forests in northern Mexico for the winter (occasionally some go to southeastern U.S.). When spring comes, they start north again, but they stop to breed along the way. It takes two or three weeks for each generation of eggs and caterpillars to mature into the migrating adults. That new generation continues northward, and again they stop to breed. It may take three or four generations for monarchs to reach their northern-most range, where they produce the long-distance travelers to Mexico. There is also a smaller population of monarchs west of the Rockies; it migrates to California and northwestern Mexico. But monarchs are in deep trouble, due to habitat changes that reduced the availability of milkweed plants on which the larvae feed and to serious deforestation in their particular overwintering sites in Mexico.<\/p>\n\t\t\t\t
Painted lady butterflies do something similar. From wintering areas in Mexico they migrate northward in multiple generations to the Canadian border; the European populations migrate from south of the Sahara Desert in Africa to northern Europe and even Iceland, making several breeding stops on the way. Red admiral butterflies winter in southern U. S. or southern Europe and commonly migrate north in spring, but shorter distances than the painted ladies.<\/p>\n\t\t\t\t
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