Another option would be to register with your local birdlist server. I frequently ask folks there for ID help and they enjoy getting good views of the birds I photograph.
Thanks for your suggestions. I'm trying out the websites and will contact folks in the area where I got the photos. I'm thinking that perhaps these particular birds were duck hybrids.
Funny thing -- I was "just" going to label all the birds I had shot recently. But after the first several coots, the very next ones in the batch were these showstoppers Seems to be the way things go!