Migration of the arctic tern
The migration of the Arctic tern is by far the longest normal migration of any known animal. Its migration starts up at its breeding ground around the arctic circle (northern Canada, Alaska, northern Russia, coast of Greenland). Then it goes winding down all the way to Antarctica for the summer there. It can be found feeding and flying around the coast for most of their time there. When their summer there is finished they go up the coasts of many different country, barely ever landing. They finish their migration back up in their breeding grounds. They have just concluded their 19,000 kilometer (12,000 mile) migration from the north to the south of the globe. During the whole year they migrate up to 70,900 kilometers. In a lifetime, the normal length of how much they have migrated is around 2.4 million kilometers.
Migration Reasons
The arctic tern usually migrates because of breeding reasons. They breed up in the northern parts of the arctic ocean and around the coasts, as well as places like Alaska and northern Canada. Another reason they migrate is because the drop in temperature over the winter in the northern hemisphere. They migrate down to Antarctica for food, rest, and for the warmer summers than the Arctic.
How they find their way around
They find their way around by the Earths magnetic forces. Having a little magnetic "compasses" in their brains, it is convenient for them. They know when to migrate from the drop in temperature in the northern hemisphere. This also indicates for when the new age of birds to come along and do the same migration as their parents and the other birds before them.