Butterflies, Blooms, Birds & Bugs

Well, it is a stabile trait, almost half of the male Mallards in the bay of Constance look more or less like this guy, tho' his bill is a bit special, most got a bit yellow-brown blotches, not this dashingly perfect black leather looks..
All are a little bit different but close to the breed Pomeranian duck in typical colouration, with blackish rather big bodies and a wide pure white bip.
Once a few years ago I found and photographed a very dark smashing Netta hybrid drake like no other in Staad and a biologist I asked said the mallard parent of that cutie might have been a melanistic domestic form, a pommeranian or a black bipped running duck perhaps, but no dark bay duck. The secret would lie in the upward turned bum giving forth a dabbler parentage.
Pure Pommeranians are also likely to be found in Germany in just any place, not breed comercially for mainstream meat consumption any longer as they need space and most would die in a paultry KZ before reaching harvest age, but they got popular as rural pets never eaten and also for those who grow their own sunday roast and some humane bio meat to sell or barter.
They are a very old breed and larger than any wild mallard and when living wild with the mallards and intermix they will have vertile offspring with strong genetic traits of the breed, unlike the warty Muskovies which are about as sizable but whose children have always a few warts and can not procreate.

https://en.wikipedia.org/wiki/Pomeranian_duck