Bird migration is one of the most astonishing phenomena in nature, but since it happens largely at night most people aren't very much aware of the amazing spectacle that's occurring all around them in the spring and fall each year.
To help give a sense of the movements of many species of birds during migration, the Cornell Laboratory of Ornithology has produced a fascinating animated feature that shows the annual migration pattern of 118 different North American species. The migration animation can be viewed here.
There's also a link on the page which takes you to a similar animation which shows the particular species of bird that's being represented. If you love nature you're sure to enjoy this. Here are a few questions to ponder while you're watching: How did migration ever evolve through random mutation and natural selection? How do these birds know how to navigate their way back and forth, often returning to the exact patch of territory they departed from six months before? How do the young of the year, which have never made the trip before, know how to do it?