Here the slightly darker coloration of the Mottled can be compared to the Mallards and you can see the wider edgings and light interior markings, giving the mottled look to the plumage rather than the very solid dark of a Black Duck. The speculum was usually dark blue but would turn green at times. Here you can just see a very thin white line at the bottom of the speculum; Mallards have wide white marks above and below the speculum. Black Ducks usually have no white on the upper wing but I have detected white on the lower edge of the speculum on a few Blacks that looked to be full blooded but with their extensive inbreeding with Mallards, these may well have been 2nd or 3rd generation back crosses.