[Mystery bird] Ring-necked Duck, also known as the Ring-billed Duck (a more obvious name, in my opinion) or the Ringneck, Aythya collaris, photographed in San Francisco, California. [I will identify this bird for you in 48 hours]
Image: Pete Myers, 12 November 2009 [larger view]
Please name at least one field mark that supports your identification.
I'm calling that an adult male Ring-necked Duck, based on the eye color, the dark back, and (especially) the white "spur" between the dark chest and the grayish flanks. That streaky look in the neck plumage matches the Sibley illustration nicely, too.
Neat shot! I'm really enjoying these Pete Myers photos. Thanks for posting them.
Looks like a Ring-necked Duck (Aythya collaris) to me too, with both Scaups eliminated because of the dark back and the white sides extending up to the shoulders...
Cool shot -- you can actually see the ring on the neck!