Re: This will make some people smile!
Unless your northeastern hogs have wings, they didn't emigrate up that way from more established populations in the south. Hogs found in New York, Massachusetts or Michigan either escaped from fenced preserves or farms, or were intentionally released.
We have feral hogs in Missouri. Their distribution is patchy. When feral hogs showed up in the northeat part of the state, it wasn't because they migrated north from the Ozarks but failed to colonize any counties in between. They were intentionally turned loose by someone.