Good morning, class. It’s a beautiful spring day outside, isn’t it? We’ll soon be seeing the first robin of spring——and so, it’s a perfect day to begin talking about migration. Migration is the main strategy that animals have for avoiding adverse environments and taking advantge of rich environments. Of course, there are other stategies, too——hibernation, for example——but far and away the most common way for animals to escape poor conditions and get to better ones is by migration——a mass journey from one place to the other.

Now there are all kinds of migratiions, but the most familiar one is the sort that our robins will be experiencing——a seasonal, latitude migration. In the fall, the birds fly south, and in the spring they fly north again, in the southern hemisphere, of course, this works in the opposite direction. In both hemispheres, migrants move toward the equator when the earth chills and toward the poles when it warms. This is the way that species have been able to colonize, to use those subpolar resources that are seasonally difficult to access, that are unavailable to many living things for half the year.

Birds are certainly the most conspucious latitudinal migrants, and they’re also the most awesome. Most famously, the Arctic Tern, which is a small seabird, migrates from one pole to the other, all the way from the arctic aubpolar region to the antarctic subpolar region——and back again——annually. These birds travel roughly 70,000 kilometers a year!