I was chatting with a friend of mine about the upcoming Thanksgiving and the December holiday season and I said that I was not a big fan of turkey and preferred duck. She said that while she has never heard about duck being explicitly forbidden as not being kosher, she has never seen it for sale in any of the kosher butcher shops where she gets her meat, nor are there any recipes for it in her Jewish cookbooks. We both became intrigued about the kosher status of duck and so I looked it up and, as is often the case with religious dietary rules, it is complicated.
The Torah apparently simply lists those birds that are forbidden to eat. But the problem is that the list was compiled way back by people living in one small part of the world and it is not clear what animals some of the names even refer to and what to do now that one has to deal with animals all over the world that were not known to the compilers of the lists.
The Torah doesn’t even bother setting out guidelines; it simply lists a bunch of birds that are forbidden, and says you can eat any other bird. Because the Torah was written thousands of years ago in an archaic form of Hebrew, we can’t necessarily translate and identify all these species definitively. One of the forbidden species would transliterate as atalef. In modern Hebrew, that’s… a bat. Which is not a bird. Most people interpret it that way, assuming that the bat was thought to be some kind of bizarre bird at the time, but not everybody does. Nobody is quite sure if atalef had the same meaning then as it does now, and some early Rabbinic discussion of the Torah described the atalef as laying eggs, but also raising its young. This has led some scholars to believe that the atalef is actually some variety of screech owl, or even—this is a serious argument that was seriously made—a platypus.
There are two separate lists of birds that are forbidden, one in Leviticus and one in Deuteronomy. There are some overlaps, but there are 24 different Hebrew names for birds in these lists. Those are confidently translated by various sources into modern English and typically include the following species: Eagle, vulture (the bearded vulture, white vulture, and black vulture are listed individually), kite, osprey, kestrel, raven, ostrich, jay, sparrowhawk, goshawk, owl, gull, little owl, starling, magpie, heron, cormorant, pelican, stork, hoopoe, and atalef. Sometimes you’ll see discrepancies, like one species listed in Leviticus as “heron” and in Deuteronomy as “ibis,” despite being the same Hebrew word. Sometimes you’ll see archaic English terms, like “sea-mew” for gull and “ossifrage” for bearded vulture.
I left one out of that list, because it’s very fun. One, in the Leviticus list, would transliterate to tinshemet. What, you might ask, is a tinshemet? Nobody knows. Sometimes it’s translated as a swan, some other type of owl, or (again!) as a bat. The same word shows up again a little bit later, under a list of forbidden animals that move along the ground, grouped in with lizards and weasels. There is a minor conspiracy theory that because it referred to both a bird and a lizard, that this word was the name of a flying dinosaur that never went extinct.
Anyway, that list of birds is, obviously, total trash if you’re trying to expand it outwards and figure out what you can and cannot eat. We don’t know whether those words were referring to specific species or whole categories of birds, and certainly many more species have been discovered since the Torah was set down. Scholars, to make up for this, have tried to see the patterns in the banned birds, and then use those patterns to create rules that could apply to species new to Jews, like, say, an unusual duck native to the Americas. This is obviously a fraught endeavor if you subscribe to the belief that the laws of kashrut are chukim—totally senseless.
Figuring out arcane dietary laws are the kind of puzzles that some rabbinical scholars relish and devote their lives to addressing. Trying to figure out what the commonalities are between those animals that are kosher and those that are not to come up with general rules is an exercise fraught with imprecision and ducks seem to fall into the large gray area. So while they are not explicitly forbidden, they are not given a seal of approval either.
Deciding what is proper to eat based on the decrees of the religious leaders of sects that lived several thousand years ago in one small part of the world seems so bizarre to me, as is listening to religious leaders anytime and anywhere on what one should wear or how one should behave. But many people do.