Canada geese learn migration routes from their parents rather than inheriting them fully, so a population that is raised without a migratory tradition may never acquire one. In the mid-twentieth century, wildlife agencies restored geese to areas where they had been extirpated by releasing captive-reared birds, many of them from the large giant Canada goose subspecies. Those birds had no route to teach.
The habitat that developed around them suited staying. Mown turf on parks, campuses and golf courses is close-cropped grazing beside open water, retention ponds resist freezing, and predators are scarce. Resident populations in parts of North America and in introduced British flocks now number in the millions, and management has shifted from restoration to controlling numbers and aircraft strike risk.
What is not resolved is how flexible this is. Whether resident birds could readily re-establish migration under different conditions, and how much of the change is learning rather than genetic, is still being studied.