Even in ancient times people were observant of the birds in their neighborhood. But sometimes their close observations led to incorrect conclusions. For example, ancient Greeks noticed that they always saw swallows in spring and summer, but they never saw them in winter. Their conclusion was that in fall swallows buried themselves in the mud at the edge of ponds and waited for spring to arrive. And sure enough, when spring arrived swallows first appeared near muddy ponds, not appearing over larger lakes until the weather was even warmer. What more proof do you need that swallows spend the winter buried in mud?
Today we know a lot more about migration but we still do not know everything. We don’t know for sure how birds navigate during migration. I knew a bird bander in Chicago who claimed he netted the same bird in his backyard 5 years in row. This was a bird that migrated to S. America every year and still managed to find it way back to his backyard thousands of miles away. How? Without a Google map I get lost just driving around the block. 
Or how does a newly born bird know when it is time to migrate if it has never done it before? Or where to go if it has never been there before?
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