Does your world see migration happening as a result of what we would term refugee crises? What happened to trigger these? (There’s probably a series of novels to be written just answering that question alone!).
In terms of wildlife, which creatures migrate and where do they go? Is this an annual event or something that perhaps happens once once or twice in a lifetime?
Does your world allow its residents to migrate to other worlds, Earth even (possibly suitably disguised to avoid comment!)? And if so, do any of the residents take this offer up? What is the outlook on other ways of living?