Sitting Ducks

I know it's a poor picture, but it was a fascinating incident.  For about two weeks there have been as many as 260 ducks in the lake in front of my home.  They are considerably smaller than mallards.  Some I recognize as Buffleheads, but there are much more of a kind I can't find in my bird book.  I have never seen them on shore.  They are always in the water.
Thursday morning about seven I saw this bald eagle circling and diving at them.  I took the picture through my bedroom window and at a distance.  By the time I got outside, he was gone.
He came back about the same time on Saturday morning.   With only bedroom slippers and no coat, I ran down to the water's edge, but the eagle flew away.  Neither morning did he seem to have any duck in his beak.
What was most fascinating was how tightly they bunched together and how quickly they moved one way or the other as the eagle kept diving.  I could hear the swoosh of the water as they shifted quickly back and forth.  I wondered how they knew it was time to swim right or left or forward or backward.  It was as if they moved with one brain.
Since they never come on land, they were completely exposed.  It was the first time I realized the meaning of the phrase "sitting ducks."  But of course they didn't just sit; they banded together and moved together and, apparently, out-maneuvered the eagle.