Visit L: a pair of mating birds. the usual yellow skin near bill was red. Female crown was black, male crown was whitish.

Description: The general distant impression of the small teallike duck was darkish with two pairs of big dirty white spots on both sides of the bill. On close distance (4 meter) the yellow, dark green and black facial pattern as depicted in the field guide revealed itself. Crown of the head was darkgreen fluorescent, sometimes appearing dark purple. Underlining the crown was a white eyeline over and around the yellow spots and the green ear coverts: together these lines formed a white 'V' on the nape. The breast was chestnut colored with black dots, the side greyish. Under tail coverts were black. Between the grey flank and the black under tail coverts there was a clear vertical white line.
However, the white line between the buf breast and the grey flank however was LACKING! (Neither was the white underlining of the yellow spots and the green ear coverts present, as visible in the guides or at this beautiful picture of another Baikal teal by Koike-san.)

I did not see the wing-pattern, as the bird was swimming quietly only, and after some minutes swam into hiding between the died lotusplants which fill Ueno pond. The bird had no markings reminiscent of Wigeon, Teal or Pintail, I believed at first. However study of the photographs of Shuichi Haupt suggests a hybrid between Pintail and Baikal teal.

Afterthought: the new book "Wild birds in Japan" contains a picture of (as the caption says) hybrid Baikal Teal x Pintail. The bird of the photo in the book is strikingly similar with the bird on Shuichi Haupt's photographs, including the detail of being ringed with an old metal ring on one leg... (whether or not it is the same leg, I don't know, not having seen the original negatives of both the photos of Shuichi Haupt and the photo in the book!?)

It seems me the same bird on all visits. One homeless person told me that the bird is already since 7 years a winter visitor (this might imply that he is living as a homeless for at least 7 years in Ueno...). The nickname among the homeless for bird is the destroyer. I am not sure which species it is: perhaps a female pochard

Description of the swimming duck between the Tufted ducks: Size in between Pochard and Tufted duck. Head: brownish black with lighter brown patches near bill (hard to see at distance) Dark eye. Bill: dark grey with a light greyish band near tip. Neck blackish brown. Breast dark brown. Mantle like female Tufted Duck. Flank however more brownish mottled and along the waterline more whitish between the middle of the duck and the back of its neck. Tail spread like a small fan and held above the water, in contrast to usual posture of the female tufted ducks. Neck was elegant long and relatively slender compared with the Tufted ducks.. Posture of neck sometimes reminding of gracefully curved neck of Mute swan. So far this seems to be a description fitting a usual femal Baer's pochard. However this individual had a partial white collar on the breast! In frontal view resembling a the colar of male Mallard with respect to position and width of collar. Behavior: It allowed itself to be fed by the homeless of Ueno-park. At quiet moments times it came within arm reach of the side of the pond. When a piece of bread was thrown towards the duck, it wrestled with the tufted ducks to get it, but unlike the tufted ducks it escaped the whirlpole of struggling ducks via a long dive to the quiet lotus beds.
Conclusion: Female Baer's Pochard

Visit G and H: Perfect male, according to other birdwatchers at the spot already present since a month present. Bill pattern rather striking. Brown band around neck, which is not always visible.
Visit J and K: perhaps the same individual.

Visit L: Male.

Visit L: pale yellow eye