This afternoon, while searching through migrant Green-winged Teal in the marsh at Milford Point (CT), one particular drake stood out among the rest. What caught my eye initially was a hint of a white horizontal stripe on the bird's lower scapulars. While "American" Green-winged Teal (Anas crecca carolinensis) often show a thin buffy or whitish edge to their lower scaps, this bird was exhibiting a subtly stronger and whiter line, like a thin and faint shadow of the typically bold white horizontal stripe of a "Common" or "Eurasian" Green-winged Teal (Anas crecca crecca) - thus catching my eye. Once locked onto this bird I noticed that it was sporting a significantly thinner vertical white bar on its breast side. The bird was very easy to track as it mingled among several dozen teal.
While either of these features by itself might be chalked up to individual variation in A. c. carolinensis, I believe that their combined presence is strongly indicative of an intergrade.
The bird was a bit too distant to confidently evaluate less reliable features such as boldness of white facial lines or coarseness of flank vermiculations. What I could manage in digiscoped photos are posted below. They're of rather poor quality unfortunately, but the subject bird should be obvious enough. Please comment if you have any thoughts.