User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-3062343-20111219023622/@comment-76.69.7.125-20111220052140

...Except that the environment isn't a constant thing, which is what I was talking about. If we assume that these animals occupy an area somewhat larger than the little bits we see in the game, then it's entirely possible that happenings would change and force monsters out of the area. Bears, for example, have been known to attack human settlements if their habitat is affected by climate change or deforestation. This has been the case for hundreds of years.

Notice how I had never used the word "migration".