Migration is defined as the regular seasonal movements of animals between two endpoints. Birds are the champion practitioners of these movements.

Some of our Maine migratory breeds undergo modest migrations, like yellow-rumped warblers migrating to the North Carolina coast for the winner. Others, like bobolinks, journey all the way to Argentina for the non-breeding season. In western North America, some species like mountain chickadee and American dipper have short-distance altitudinal migrations, moving down mountains during the winter and back up again in the spring as the ice and snow melt.

Birds don’t have a monopoly on migration. Many species of fish migrate. Salmon and striped bass migrate from the ocean into freshwater to spawn and eels migrate from freshwater to the ocean to spawn. Astounding migrations of wildebeest, zebras and other herbivorous mammals migrate in the Serengeti region of east Africa, tracking seasonal rainfall and grazing opportunities. In North America, migratory behavior is seen in elk, caribou, bighorn sheep and mountain goats.

Some insects also stage impressive migrations. This column will focus on some migratory insects in Maine now. Expanding your view while birding to these insects can enrich an outing.

Most insects aren’t migratory. Most Maine insects will pass the winter in an overwintering stage. In some species the egg is the overwintering stage; in others, winter may be passed as a hibernating larva, pupa or adult. But insects that do migrate are often mind-boggling.

In some butterflies, completion of a migratory loop involves multiple generations. The best known of these species is the monarch, a species that is reasonably common now in Maine. The monarchs we are seeing now emerged just weeks ago. They will wend their way all the way down to the highlands of Mexico this fall. The butterflies will spend the winter there and begin a return trip in the spring.

The spring migration is driven by the appearance of milkweeds, the plant that monarch caterpillars require for food. The overwintering monarchs move north until they find milkweeds, mate, reproduce and die. The next generation of caterpillars emerge, migrate northward and repeat the cycle. So the monarchs that arrive in Maine to reproduce may be the great-great-great-grandchildren of the ones that migrated to Mexico the previous fall.

Spanning the year in this way means generation length is variable. The butterflies that emerge in Maine in August will live for seven to eight months, until the northern leg of their migration. The summer generations scarcely live for a month.

The painted lady is also a migrant, periodically abundant in Maine. Found on both sides of the Atlantic, painted ladies also have multi-generational migrations. A recent study showed that painted ladies take five or six generations to complete a migration between north Africa and the Arctic circle each year, a trip of some 9,000 miles.

A few dragonflies are migratory. The best known in Maine is the common green darner, a powerful flier about three inches long. Each spring they migrate from the southern United States to reproduce in northern lakes. The aquatic nymphs emerge in the late summer and fall, then begin a southern migration. Sometimes spectacular swarms can be seen.

In the past few weeks I have seen a number of wandering gliders, a dragonfly with an orange body, a tapering abdomen and speed to burn. They are about two inches long. Wandering gliders are the champions of long-distance dragonfly migration. Undeterred by oceans and even the Himalayas, this species travels broadly, occurring on six continents and most oceanic islands.

Each year wandering gliders make a multi-generational migration of 11,000 miles with some individuals flying over 3,700 miles. Watch for these marvels in your neighborhood.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

whwilson@colby.edu

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