On a recent visit to Lake Ralphine, the small lake at Howarth Park in Santa Rosa, I was pleased to see a good number of wintering ducks, including Buffleheads, Common Mergansers, A Gadwall, and a Ruddy Duck, but there was also group of about 10 Scaup.
Scaup come in two flavors--Greater Scaup and Lesser Scaup. They are very similar and hard to tell apart. I think these were mostly Greater Scaup. I'm pretty sure that at least the female pictured above is a Greater. The male (lower photo) may be a Lesser.