Migration Mysteries

Humans have watched animals come and go for millennia, mystified by what was going on. The ancients noted that some birds who are common in the summer are never seen in the winter, but come round once again in the spring. Since our ancestors tended to stay put in one locale, they had little idea of where those species of birds went, before they returned.

One of the first scholars to speculate on the annual movements of birds was Aristotle, who—some 2300 years ago—decided that Greek swallows (who disappeared over the winter) dove into lakes and ponds and slept the cold months away, buried in mud. He also claimed that the redstart (an African songbird with a red belly) transformed itself into a robin (with its red breast) in the fall, then back into a redstart in spring. Such was the stature of Aristotle that these beliefs persisted for over 2000 years.

So, only relatively recently (beginning in the 18^th century) have we come to understand that some bird species migrate seasonally—primarily seeking sources of food. An insect-eating thrush spending its summer in New England is bound to starve if it attempts to overwinter there, so evolution has taught it to fly to Latin America for the winter, to feast on bugs down there.

The astonishing feats of many migrating birds have been documented—but many mysteries remain. They are gradually being solved with sophisticated scientific studies. The distances they travel boggles the mind. The Arctic tern flies 20,000 miles from the Arctic to the Antarctic and back! It's the long-distance flight champion of birds.

The seasonal destinations of migrating birds is now pretty well known, through the use of various scientific tracking devices, but many riddles remain about how birds do it. How does a thrush leave its hollow in the woods of New England, fly to a certain hillside in Panama, and return to the same hollow next spring? It is known that birds use a spectrum of techniques—the Earth's magnetic field, the position of the sun and stars, landmarks such as rivers and mountains, even following roads—but specifically how a given species does it is still being sorted out.

Birds are not the only migrators, however. Whales seasonally journey up to 12,000 miles, but are tough to follow, since they do it hidden underwater. The Monarch butterfly travels from as far north as Canada to one specific mountainside in Mexico.

Then there are other mysterious movements made by some critters that are not necessarily seasonal, but still remarkable, in that they travel significant distances and unfailingly return home. Honeybees use various landmarks, as well as the sun's position, to return to their hive and describe to their hivemates the exact location of the pollen and nectar they've found, using the “waggle dance.”

Recent scientific studies have shown that pesky garden snails plucked from the veggies they are chewing on and transported up to 60 feet away, will navigate back and resume their meal. I learned years ago that a box turtle we found dining on our tomatoes and then carted several hundred feet into the woods, would just be back the next morning. That's a better homing instinct than I have! A few times I've wandered as little as a half mile into the forest and became disoriented. Good thing I have never tried to walk to Panama... I'd never come back!