Good Santee Lakes news: I found the previously reported Least Bittern at Lake 7 with no problem (go out onto the floating motel rooms dock to scan the reeds for it).
Weird Santee Lakes news: In Lake 2 (that has the Mast Blvd bridge over it), on the W side just N of the bridge was an immature duck that defied ID-ing. I’m pretty sure it was a merganser going from juv. to adult plumage (making the assumption that all adults would be in alternate plumage by now). Most things on it looked like some manner of COME, but one major one (flank color) was clearly different from anything shown in Sibley or Nat. Geog. (herein “NG”), and more resembled the brownish flank color of an adult male Hooded Merganser.
Things that looked like a COME: The entire throat and breast were bright white, there were black “speckles” in the chin area, as shown in NG (but not Sibley), and the bill was bright yellow and clearly thick at the base (as NG points out in its “1st spring” depiction of a COME). Also, the head lacked the elongated horizontal rear head feathers characteristic of both HOME and RBME. Its legs were bright reddish-orange. It had linear downward black feather patterns coming in from the rear neck area which were longer than the short extension on a COME but did not go all the way to the water line as per a HOME. The head lacked the oval shape of both the HOME and RBME. Perhaps most importantly, it was large, looking at least 50% longer than the coots swimming by; i.e., much larger than a HOME.
Things that looked like no depiction in either Sibley or NG: The top of the head and nape area appeared black (not dark green), and had some white dots and the white portion had black dots. This could perhaps just be that the plumage change was only half-way complete.
Things that looked like a HOME: As noted, the flanks were brownish, somewhat similar to both books' depiction of an adult male HOME, except that the lower belly area (the area where a wigeon would be black) was white.
Things that didn’t look like a RBME: the black line(s?) going downward from the neck, the pure white upper breast and front half of neck area, and the lack of linear feathers extending out and back from the head.
Overall, given the bird's large size, bright yellow bill with wide base, head shape, and a few other details, it seemed to most closely resemble a COME. (Unless someone wants to make a case for a hybrid.)
Perhaps the main question would be: Despite the lack of any such depiction in either Sibley or NG, could a juvenile COME ever have brownish flanks?
I’d appreciate any help anyone could extend as to getting a positive ID for this annoying teenager. If anyone lives near east county, you might be intrigued by a first-hand look at this mystery bird in Pond #2 at Santee lakes.