Guild Wars 2

This would be really neat for making it feel like a living world as Anet is going for.
Some animals or mobs could move every so often to different spots, or have patrol routes.
Migration is what animals do in real life so this would be neat to do.

Already in game. See moas in Plains of Ashford, they run around. But agreed, they should add larger routes and they should do this for aquatic animals also.