The great migration south is about to begin. It will include millions of birds, millions of fish, many different bats, and quite a lot of butterflies and dragonflies. Although at the boreal latitudes, many mammals, including two species of caribou, use their legs to march long distances, in the temperate zone where we are, migration is a matter of wings and fins. Shorebirds, terns and ospreys, to name a few, have already started down. Some of them go thousands of miles, deep into South America, a few like the Arctic tern, all the way to Patagonia.