The suffix -tion forms nouns of action and condition. Migrate means to move from one region to another, especially regularly according to the seasons. Like... The birds migrate from point A to point B every year. Migration is basically the same as migrate, with subtle usage changes. The definition is virtually identical. For example, you can use this word like this: The migration of these birds every year is magnificent to watch. They are almost noninterchangeable. For example, you cannot say "The migrate of these birds every year is magnificent to watch," or "The birds migration from point A to point B every year." The latter has actually become a dependent clause, but that's irrelevant to your question.
Sorry if my answer is a bit confusing, but hopefully that answers your question.
