Migration, how it evolved, what triggers it, how birds know where to go, has puzzled humankind for a long time.
While its mechanisms are fairly well understood today, it was not always so. In fact, Aristotle believed that small birds, such as larks, swallows and turtledoves, hibernated. This misconception was kept alive by stories of swallows being found frozen in wetlands, then flying off after thawing.
Another tale that persisted for five centuries in northern Europe until the 1600s was that Barnacle geese arose from goose-shaped barnacles that rode ashore on pieces of driftwood. During those medieval times it was not known that these geese nested in the Arctic, for the Arctic was not even known to exist.
Such migratory anecdotes, as silly as they sound, are still common even today. For example, the American coot, a very abundant chicken-like species of waterfowl, has been accused of never migrating. Instead, as the story goes, they hibernate in the mud on lake and marsh bottoms. This was probably fueled by the fact that one rarely sees coots migrating. They, like many birds, migrate at night and so go undetected as they leave each autumn from their breeding grounds.
Another far-fetched migratory account involves hummingbirds. It was once believed that hummingbirds hitched rides on large species of waterfowl like geese and swans. Of course, this is false. Hummingbirds are true champions of migration. Ruby-throated hummingbirds migrate enormous distances each year that includes Alaska, across the Gulf of Mexico and South America.
But why do they migrate? How do they know where to go? These are just a couple of the many questions that ornithologists, naturalists, and many other people have been asking and studying for generations. And though many answers have been formulated, not all questions have been answered definitively.
For instance, some populations of the common ringed plover migrate, while other populations of the same species do not. Why do some species of birds choose the wintering and breeding grounds that they do when sites just as suitable lie, in some cases, thousands of miles closer?
Arctic terns, for example, travel a whopping more than 15,500 miles, round-trip, from their high-Arctic breeding grounds to their Antarctic wintering grounds and back again every spring. Many woodland nesting warblers nest throughout northern United States and southern Canada, but winter in Central America and in the West Indies.
The energetic cost of migration is tremendous, too. It is estimated that half of all the small birds of the Northern Hemisphere that migrate to southern climates never return to their northern breeding areas. It is also estimated that more than 100 million North American waterfowl annually migrate to southern wintering grounds, yet only 40 million make the return trip the following spring.
Researchers studying why some birds fly in formation, like ducks, geese and pelicans, have determined that - in the case of pelicans - their heart rate decreases 11 and 14-percent when flying in the conventional "V" flight-pattern. It was also discovered that pelicans beat their wings less frequently when flying in formation than those solo flyers do. Thus, the birds flying in formation were able to glide more and expend considerably less energy while in flight.
The reason that many birds migrate is usually food-driven. Ducks and geese would have no problem spending the entire winter right here if food and water were readily available. And some actually do remain behind if conditions are right. But how they migrate is even a more intriguing question.
It is believed that migration is possible because of a combination of factors. With some birds, navigation is accomplished through learned experiences across known routes, over known landmarks, to known destinations. Still, too, the stars and sun play important roles for those species of birds migrating during the night and day. And stranger yet, the geomagnetic fields of the earth provide some species a means of orientation. Even olfaction helps some birds, like pigeons, literally smell their way home.
Lastly, something else to think about; by preparing now you will be more than ready for the influx of migrant birds that are sure to arrive. Keep your bird feeding stations filled with a variety of birdseed, your suet feeders filled with high-protein essentials, and your bird baths filled with water. As well, put out a tray of grit or fine grain sand for your birds to pick at and dust themselves with.
Come mid-May the ruby-throated hummingbirds and Northern orioles will return, so be sure to be ready for them, too, by having your sugar-water feeders filled and hung outdoors. You might also consider purchasing meal or wax worms for your insect-eating birds such American robins, eastern bluebirds and phoebes. A small bowl filled with these tasty morsels will be appreciated by these feathered friends if we have an especially cold spring.
Indeed, the annual migration is once again occurring here in the Northland. The spring migration - this amazing spectacle, this yearly awakening - is one of the best times to get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org.