Canada geese

Yesterday I saw a flock of seven or eight Canada geese near a pond on Weaver Dairy Road here in Chapel Hill. So many have ceased migrating and taken up permanent residence here that they are widely regarded as pests. The curious thing to wonder about, though, is why so many stopped migrating in the last fifty years. Geese in permanent residence were unknown seventy years ago, now there are large colonies in several mid-Atlantic states. Birds migrate for a variety of reasons--seasonal availability of food, inclement weather, to find breeding partners, to find nesting grounds that are free from predation, disease, and parasites among them--but my reading suggests that migration is largely instinctual. Cage a migratory bird and it will become restless and agitated when it would migrate if free. That the geese can give up their migration in a few generations, and that successive generations don't seem to feel the urge to migrate, either suggests that the seasonal migration of geese is learned.

I've heard that deer in North America once migrated seasonally, but stopped in the nineteenth century when their numbers fell precipitously due to overhunting, and that once the generation who knew the migration patterns died off, succeeding generations never took it up again.