Birds on the Move: Migration Made Simple
By Sue Corcoran
Man has long been interested in the phenomena of birds that disappear in the autumn and reappear come spring. Aristotle thought that delicate birds morphed into hardier species and changed back only with the return of warm weather. After additional observation, he declared that small birds, notably swallows, burrowed into the mud at the first sign of winter, hibernating there until spring. His theories of transmutation and hibernation were the prevailing wisdom for over 2,000 years. Until the 17th century, it was unthinkable that small birds were capable of long flights.
Today we know billions of birds leave their homes every year and travel a significant distance in search of food and optimal nesting locations. More than half of the birds that breed in North America are migratory. Their migrations can cover thousands of miles, last for weeks, and encounter dangerous conditions. The routes they take( called flyways) and the places they stop for much-needed rest and refueling( called stop-overs) have been the same for centuries. Or so we thought.
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