If a diver gets up more than twice a day--they will looose weight and they are trying to put on wieght (fat stores)in the fall for the next leg of their migration. Often they use 20% of their body weight in 1 leg of the migration.
And there is the being disturbed part too. If you keep being bothered, as pointed out above, you will go elsewhere. I believe this is indeed a big reason there are fewer ducks in MN-not just divers. In 1978 at 1 large marine dealer, the average boat and motor sold was 14' with 15 hp, in 2003 it was 18' with 115 hp motor. Ever notice the run and gun (also known as cast n blast) fishermen in the lakes in the fall now? Pretty rare to even see 1 fishing boat in Oct on a lake around 30 years ago. Now they race all over the place. Heck, I have a finger pointed at myself in motor size
. In 1978 I used to use a 5 hp, I have a 25 hp motor now. Still small compared to most fishermen of today, but nonetheless you see the trend, and I am guilty of it too. Hunters as well as fishermen are adding to the problem, but the huge 100+ hp motors of the fishermen zipping across the bays repeatedly all day long has forced the divers virtually out of MN along with the lack of sufficient food (due to poor water quality -its been greatly degraded).
And some wonder why there are no divers in MN anymore.