Where birds go during the winter, and how they get there, has baffled people in the northern regions of the world for centuries. Aristotle suggested that birds changed species with the seasons; that redstarts turned into robins and garden warblers into blackcaps as the weather cooled. As late as the 19th century, some naturalists thought birds hibernated.
The reality seems almost as crazy as birds morphing species throughout the year. Thousands of bird species (at least 40 percent of the world’s birds) travel between summer breeding grounds and winter enclaves, sometimes crossing continents and oceans to do so. For example, every year, the arctic tern travels 44,000 miles on a meandering path between Greenland and Antarctica. However, seasonal migration is not restricted to flying birds. Emperor penguins march across 70 miles of ice each year from the sea to their breeding ground.
via Mental Floss
