Ruddy Duck - Oxyura jamaicensis

Ruddy Ducks are diving ducks in the subfamily (tribe) Oxyurini, the Stiff-tailed Ducks. In winter they are plentiful in the Bay Area, and are one of the species least bothered by human presence. At the Las Gallinas ponds they can often be viewed hanging out pretty close to shore, which may explain why I like to photograph them. Here's the female, seen at the southwest corner of pond #1. Head/bill profile pretty distinctive. Unlike the male Ruddy, she won't change a whole lot as the season progresses.

The male Ruddy Duck is easily identified by his white cheek, but in his early winter "basic" plumage he is otherwise much like the female. Note the stiff tail, a feature easily seen at a distance. The female can also raise her tail, but perhaps does do less often. As the winter progresses the bill color of the male will become dark blue, presaging a more dramatic high breeding plumage. 

An older photo shows how the male will look in the spring, with full ruddy color on the body, darker cap and tail, and unreal sky blue on the bill. Taken at Shollenberger Park in Petaluma some years ago.

Ruddy Duck - Oxyura jamaicensis

At the Las Gallinas Ponds redently the high water level seems to have displaced many of the dabblers, but good number of "female" Ruddy Ducks were noted, along with a scattering of males. Ruddies are active divers, but this one paused for a few photos. Note how the dark line on the face extending back from the bill is somewhat indistinct.

The presence of what seemed to be a disproportionate number of female ducks got me to wondering. Similar situation with the Buffleheads, where female type birds often outnumber the males. I think it's best explained by the fact that in many bird species the young birds of both sexes bear a strong resemblance to the adult female in non-breeding plumage. Thus, in viewing a flock of fall Ruddy Ducks we are likely seeing a mix of adult male and female Ruddy Ducks, along with the hatch year birds of both sexes that look a lot like mom. Here's another shot of the same adult female:

If you look at field guides you'll see relatively few drawings of juvenile ducks, so it's hard to hard to learn the subtle clues to tell the young birds from the drab adult female. With the Ruddy Duck the males are easy to pick out, as they have a white cheek patch year-round. This one from a while back, taken in December:

And here's a spring male in full breeding color, just in case you were wondering where the "ruddy" comes into play. Note also the cocked-up tail, a hallmark of the "Stiff-tailed Ducks":

The cheek of the female Ruddy Duck is also white, but is interrupted by a dark line, faint or blurred in the non-breeding female as in the first 2 photos, and well-defined as she enters alternate plumage in late winter/spring (drawing below).

Ralph Palmer, in Handbook of North American Birds (vol. 3, Waterfowl), describes the rather complicated molt cycle of the Ruddy Duck, but in a telegraphic ponderous manner that is difficult to absorb. Fortunately he included drawings by Robert Mengel, which I attempted to capture in the attached shot. Text labels were added by me, following the author's explanation. 

Mengel was a highly regarded multi-talented naturalist/artist. Good bio piece at:

 

Robert M. Mengel - Biography