Well migration patterns are based on the earth's magnetic field - which is weakening, although different species' migrations are affected by different things, not just magnetic field. We also see that the positions of the magnetic poles have been shifting (for example, the south pole has left the continent of Antarctica entirely). As the poles shift, so will the migratory patterns, so you could see flocks of things that you haven't in the past. The circling thing though, I don't know if that can be explained by this shift and weakening field?