These are Ring-necked Ducks. Notice the female with her wings stretched, showing the coloration beneath the wings. The males have white sides. Their bills have a white outline near the base and a white band near the end with a black spot on the tip. These ducks were in a temporary pond in a farm field.
A male Bufflehead cruises the waters of Summit Lake. It is seen below next to a Coot and is about the same size. The stark contrast of the black and white coloration is striking.
Here a male and female Bufflehead are seen for comparison. The female has a much smaller white patch on her head and her side is brownish instead of white.
These are Horned Grebes as seen at Summit Lake State Park. They are in their winter plumage and are just beginning to transition to their breeding plumage.