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Aristotle lived 2,400 years ago, in the fourth century before the common area. He was a Greek philosopher in the literal meaning -- a lover of wisdom. Among his many interests was the natural world. As a naturalist, he observed and reasoned. Science in his day did not consist of experimentation or testing of theories. There was little lab work. Why bother when the mind itself could arrive at conclusions through its own powers?

Among Aristotle’s vast output was his 10- volume "History of Animals." In this work, he refers to about 140 species of birds; some of his references to birds were on the mark. He knew the migration pattern of some large birds, such as Eurasian cranes. He described how other birds migrate from higher altitudes to lower altitudes. He observed that birds setting out on migration were fatter, and that those returning from migration were thinner. Today it is a given that migrants bulk up before departure and that they burn those fat reserves during their long flights, but it took 2,300 years before scientists elaborated much on Aristotle’s observation.

Aristotle’s travels were limited to the "civilized" world, which was restricted in the Greek mind to what is today Greece and Western Turkey. He might have watched cranes, for example, flying over head. Then he gathered reports from travelers who saw cranes in the marshes of the Nile River during winter, and from other travelers who saw them on the steppes north of the Black Sea during the summer. From this he was able to conclude that cranes migrated.

Unfortunately for Aristotle, it is not some of his astute observations and conclusions that are best remembered among naturalists today, but his mistakes. For example, in Greece there are five species of swallows, small, fast flying, insect eating birds. (One of them is the same barn swallow that nests in our barns, garages, and porches.) Aristotle knew that these birds disappeared during the winter, but he had no reports of them being anywhere else in the known world. In addition, I would imagine that it was inconceivable for him that such small birds could make a long journey. So with very thin evidence, he concluded that the swallows hibernate in the winter -- hidden in holes, crevices, or hollow trees.

Try not to laugh. His conclusion was accepted wisdom for over 2,000 years. In the mid-1500s, for example, the Archbishop of Uppsala in Sweden strayed from theology to natural science and declared the hibernation of swallows as "fact." When science began to enter the experimental stage, some researchers tried to induce hibernation in swallows by locking them in icehouses; the results were fatal.

Our American bird watching hero, John James Audubon, did a great deal to revolutionize the understanding of bird migration. He knew that many birds moved seasonally long distances. But old "facts" die hard. In 1878, Elliot Coues, one of the founders of the American Ornithologists’ Union, was convinced that the insect-eating swallows followed food sources south; he knew they migrated. But he could not ignore the possibility of hibernation. He listed "182 publications dating back to 1630 that accept the possibility of swallow hibernation." He admitted that hibernation was "well attested, according to ordinary rules of evidence." He told his readers to weigh the evidence and make up their own minds.

Are you laughing? Try to imagine Aristotle standing in Capistrano when the swallows return. Two millennia ago, travel was slow and difficult. There was no way to track bird movement; the few ships that successfully returned from the "ends of the earth" were just glad to have survived. The rare person on board who might have been a curious observer is unlikely to have noticed tiny swallows flying about, and connect those swallows to the ones nesting in the stables at home in the summer. So when the swallows suddenly appear at Capistrano, is it so odd to conclude that they have emerged from hibernation?

I know you are still tittering. Let’s put Aristotle on Harvard Square in Cambridge, Mass. He has concluded, logically and rationally in his mind, that some birds hibernate. It is quite easy in September to observe a small warbler in the Cambridge neighborhood (and all along today’s New England coast) that is feeding voraciously. If we are observant, and it is quite likely that Aristotle was keenly observant, we will recognize that this small warbler is a blackpoll warbler in its rather dull, nondescript winter plumage. One day the bird disappears. Gone. With his students listening raptly, Aristotle tells them that the tiny warbler has gone into hibernation.

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And you are laughing again! No, no, no, you say. This tiny blackpoll warbler has departed on its migration. Weighing about a half ounce, for the next four days it will fly 1,800 miles nonstop over the Atlantic Ocean until it reaches the coast of South America, and then it will continue to southern Brazil and Bolivia. And Aristotle will tell you that if you are going to propose an alternate to hibernation, at least it should be reasonable and believable!

So you try again to counter Aristotle’s hibernation theory. The ruby-throated hummingbird (it weighs about 0.11 ounce or 3.2 grams) that returns to the maintained gardens of Cambridge in early May, spends the winter somewhere in tropical Central America. On its journey north, it flies across the Gulf of Mexico from the Yucatan to the Mississippi Coast, then continues another thousand or so miles north to New England. With as straight a face as possible, Aristotle asks if you are seriously proposing this as a reasonable and believable alternative to hibernation. His students are less restrained; they are rolling on the Harvard Square grass -- or wondering where they can get whatever it is that you have been smoking.

After the breeding season, the swallows in Greece migrate to Africa or southern Asia. Aristotle had no way of learning this. He knew of animals that hibernate, and came to the reasonable conclusion that the swallows also hibernate. Writer after modern nature writer will recount this "ridiculous" conclusion on Aristotle’s part with barely concealed derision, as though the "true facts" were not even more outrageous and beyond belief.

Bird migration is fascinating and astounding. It is no surprise that Aristotle could not conceive it for his swallows and postulated, instead, hibernation. He was wrong about the swallows. But -- I hope you are ready for this -- he was not wrong about hibernation. Some birds do hibernate. More soon.

Good birding!

"The Migration of Birds." by Janice Hughes (Firefly Books, 2009) tells the fascinating history and science of migration. It is a rarity in the book word -- a glossy, small-sized coffee table book that demands reading. I’ll be returning the copy I have to Brooks Memorial Library in a couple of days.

Chris Petrak is a birding hobbyist who lives in South Newfane. Photos of the birds he writes about can be seen at