When I think of Bigfoot "migration", I prefer the Cromagnon, or Neaderthal, perspective. Of a small clan of a few families, moving dependant on the environment and their successful existance within an area. The term migration, can't really be used in this context, as in other animals that travel for seasons, over vast areas, for food or breeding times. It also depends on the "culture" of the groups, the learned and instinctual survival techniques passed down for generations, within their geographical area. Movement of groups in the California/Oregon, would be different than in deep Canada, actic zones. Ancient man had migration zones, dependant on seasons, higher or lower elevations etc, but rarely went beyond their inherited areas, unless run out of them by larger clans, or environmental problems. Why leave what works for you?

Genetic differnces can be seen in some of the sightings, hair color, size, aggression levels, curiousity levels. This tends to show a set movement area, within their cultural limits, with changes in their dna expressions coming from their new environments. Loose males, as in other species, may be run off, and move into new areas, steal a female, or kill a lead male, start their own clan, etc.. Speculation there, but, the ancient human, or even the chimp clan setup seems most plausible.