Swallow Migration

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In Late and Middle English, the word “swallow” meant “gulf, abyss, hole in the earth or whirlpool,” and later “throat or gullet.” The Norse version of the word meant “devourer or swallower.” Today it means to put a drink or piece of food down the throat, accept a story without question, or the familiar small bird that frequents our skies in the spring. Swallows are amazing animals, flying as much as 600 miles a day in pursuit of flying insects. The eight species of swallows that breed in North America journey to every part of Central and South America every year. Swallows in the U.K. fly 6000 miles south to their wintering grounds in Africa.

Tree Swallow

In The History of Animals, Aristotle made a number of astute observations about birds: they all lay eggs, most build nests, and the hard-shelled eggs have yellow and white parts inside. This information was easy to obtain by diligent observation. But he also made incorrect assumptions; for example, he thought that females were hatched from pointed eggs and males from rounder ones. What he based his information on is unknown, but the conclusion was clearly wrong.

One of Aristotle’s most noteworthy incorrect observations had a major effect on bird science for many years. About 350 B.C. Aristotle observed swallows appearing in the spring and disappearing as winter approached. He also watched them dipping into the surface of lakes and ponds, and sitting on emergent vegetation. Without any other evidence, he decided that swallows burrowed into a lake or pond bottom to spend the winter. Hundreds of years later a 13th century legend depicts the Christ child playing in mud and forming birds. In medieval Europe there were reported observations of so many swallows sitting on vegetation above the water that the vegetation dipped over into the water, taking the swallows with it. In the mid-1500s Olaus Magnus, the Archbishop of Upsala, published a book containing a woodcut of swallows being fished out of the bottom of a pond. He claimed that if you brought them into a warm room, they would begin to fly around. Even in the 18th century, swallows were thought to hibernate in the mud, in tree cavities or between rocks, after denuding themselves of feathers. See The Swallow That Hibernates Underwater.

Swallows being netted from a pond

In the late 19th century, a famous ornithologist and founder of the American Ornithologist’s Union, Eliot Coues, cited numerous past studies to give credence to this hibernating in the mud theory. Coues said that some reptiles and mammals hibernate, so why would one not accept the idea that swallows also would? The most fascinating part of this story is that Aristotle’s total speculation was taken as fact for nearly two millennia. The consequence of inadequate scientific method and the vast unknown of the early natural world was society’s willingness to believe all manner of unalloyed nonsense. (Are we that different now?)

In other ways, Aristotle was astute: For one swallow does not make a summer, nor does one day; and so too one day, or a short time, does not make a man blessed and happy.

5 thoughts on “Swallow Migration”

  1. Pingback: Rough-winged Swallow – Ornithology

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