Common Teal (Anas crecca crecca) form of Green-winged Teal on the AOU list, also known as Common Teal (Anas crecca) on BOU list.
Note the presence of the horizontal white stripe along the scapulars (Anas crecca crecca field mark), and the lack of a vertical stripe on the side or a buffy base to the chest (Anas crecca carolinensis field marks). Anas crecca nimia, of the Aleutian Pribilof Islands in Alaska, would resemble crecca crecca, only with the horizontal white stripe replaced by a line of oblique white-over-black slashes. If you happened to have one of each in your hands, you would also see that nimia is larger than the other two.