According to the Cornell Ornithology Lab's All About Birds web site, [the Ring-necked Duck] is the most common diving duck to be found on small ponds in migration. It is more easily recognized by the bold white ring around its bill than the chestnut collar for which it is named. If you enlarge the bottom photo (double-click on it), you can see the chestnut ring. I wasn't able to isolate any females to photograph in Agua Caliente Park, but I believe there's a female on the far left of the group photo.
