Guess I had just assumed this was a local problem here in western Washington and Oregon- same situation- 20 years ago you could barely make out the geese flying over, then they decided to move in year around.  When you think about it, it's a pretty big deal, biologically speaking- an entire species drastically changes the migration patterns it has followed since the beginning of time, and they all seemed to decide on it simultaneously- did they have a little convention somewhere?