Green sheen, ageing feathers, and proposed ancestry

The British Waterfowl Association explains the green sheen as an effect of feather structure and light rather than green pigment applied to an otherwise black bird. Similar lustre appears in other dark domestic ducks. Color photographs therefore depend partly on lighting and angle; one dull image cannot define the whole breed's appearance.

The association also describes whitening with age, more often in females. Age should remain attached to captions and comparisons. Its discussion of possible American Black Duck ancestry is explicitly uncertain, not a reason to replace the domestic breed's scientific identity with a proven hybrid formula.

The reported seasonal fading of dark eggshell pigment agrees with the need to identify when an egg was laid. Plumage, eggshell color, and ancestry are separate biological questions. Together they make a richer teaching profile than simply calling the Cayuga a black duck.