Here is the only place that I know of where the issue of birds, clean and unclean comes up in Scripture is in Deuteronomy:
14:11 [Of] all clean birds ye shall eat.
14:12 But these [are they] of which ye shall not eat: the eagle, and the ossifrage, and the osprey,
14:13 And the glede, and the kite, and the vulture after his kind,
14:14 And every raven after his kind,
14:15 And the owl, and the night hawk, and the cuckoo, and the hawk after his kind,
14:16 The little owl, and the great owl, and the swan,
14:17 And the pelican, and the gier eagle, and the cormorant,
14:18 And the stork, and the heron after her kind, and the lapwing, and the bat.
So not sure what to say, but I have eaten duck after I became a Seventh-day Adventist.
My understanding was that any bird that eats flesh is not to be eaten. Any animal that eats flesh is not to be eaten.
So where do ducks fit into this I do not know.
Will still research.
Liane, the Zoo Mama