This seemed seasonally appropriate, given that I watched some migrating geese fly over today.
Migrating geese fly in V-formations so that the majority of them can take advantage of the updraft in the outer part of the wingtip vortices caused by the goose in front of and to one side of them. The lead goose in the middle does more work than the rest, so occasionally they drop back, forcing one or the other behind them to take the lead. The one on the other side of the former lead goose drops back too, then the next, and so on, causing a ripple along that side of the V, of geese dropping back a bit one at a time.
Very similar to velodrome cycling teams "drafting" behind a leader, who will periodically move out of the lead and drop back to the end of the line of their teammates.
Quiz time.
Q: Why is one side of a V of flying geese usually longer than the other?
A: Because there are more geese on that side.