While I was watching a white duck swimming with many Mallards and Gadwall in Jenney Mill Pond a pale brown bird drifted into my field of view and begain swimming in synch with the white one. Its pale tones reminded me of the 1st year Kumlien's Gull being seen at the town pier. The two stayed together most of the time and seemed like they might be a pair (the Gadwalls and Mallards already seem to be pairing off for the spring). At first I wasn't sure whether they were aberrant Mallards or Gadwall. I concluded Mallards based on head shape, the shape and color of the bills, and for the clincher, when the white bird occasionally vocalized, it gave a classic Mallard call.

This series of photos shows the white bird by itself, with the pale bird and also with a hen Mallard for reference. I can't tell the gender for certain though I understand that the typical Mallard quacking sound is made by the female, and that, coupled with an obvious eye line, suggests that the white one is likely a female. The presence of some silvery back feathers, the absence of an eye line and the yellowish color of the bill suggest to me that the pale brown bird is likely a male. I tried to use bill color to help differentiate, but I can't find clear guidance on this point. One wonders if these two were to breed whether they would have success, and if so, what the offspring would look like!

Two more interesting birds at Jenney Mill Pond! (addendum..I found the white bird again on 1/24 at Store/Spooner Pond in N. Plymouth)