Saw the feet of the black birds that I saw last week

I saw 7 of the black birds, and several were standing on rocks. A white duck was with the black birds, an I was able to compare the feet of the ducks with the feet of the birds. The birds do not have webbed feet. They are larger than male Mallards. Their bodies aren't coal-black, because there are areas of dark gray mixed with areas of black. There is a thin white strip near the ends of the wings.