Yep, exactly. But there are other resources like deer, whales, fish, etc. that would still move around, right?
I like this idea, especially for the whales, but it brings up several issues.
First lets start with deer. Deer don't really migrate, they follow a set path each day between feeding grounds, bedding areas, and such. This routine is basicly the same every day, same feeding sights at the same time, same crossings at the same times. On a civ map this, at most, would be confined to a nine square block, but really wouldn't be more then 2-4 squares of area.
As for beavers, I've heard tell of them traveling several miles to get the proper timber, but they don't really migrate around at all being centered on their lodge.
Fish are a complicated issue, in that many species migrate long distances, but there are also just as many that live in the same square their entire lives.
It would seem to me that there needs to be several movement templates.
1) When resourse created, the initial square and X adjacent squares are chosen and the resourse moves either randomly(ie beavers) around them or in a set path from Tile A => Tile b => Tile C => Tile A => repeat(ie deer).
2) When resourse is created, initial tile is stored as birth tile. The resourse then spends some amount of time in that tile(maybe moving between that tile and adjacent ones) before migrating to another area of the map. This would be the basic idea of whales and could also be used with fish.
3) Pertaining to fish I think the above template should be used on some fish resourses, but inaddition to that, other fish resourses should not move at all, and otheres should move around in there birth tile and adjacent tiles.