I'm guessing that you mean migration. Anyways, if that's the case, then migration is when you send a pokemon from a previous game to a newer game. By doing so, you won't be able to send the sent pokemon back to the previous game.
ie. you have pokemon emerald and you send Latias over to platinum. You won't be able to send latias back to emerald because of changes that could've been done like teaching Latias moves that didn't exist in emerald.
Your question "Can navel piercing migration be down to growth" makes no sense.
Yes. I live just north of Orlando, Florida and there's a lightning bug flashing on my back door right now. However, I've never seen more than one or two at a time in the past ten years I've lived here. When I lived in Ohio, as a child, there used to be thousands in the yard at night. I don't know if there naturally aren't as many lighting bugs in Florida, or if they're disappearing everywhere.