Lévitique 11:13

And these kinds of birds must be abominated: those not a finger long, or that have no vesicle (zephaq), or whose crop (kurkeban, ingluvies) peeleth not away, are not to be eaten they are abomination; the eagle, the black eagle, and the osprey,

Of the fowl you will detest The precise meaning of the word “you will detest” is slightly different here than in the phrase “Do not make yourselves detestable” [:43]. There, “yourselves” is the direct object of the verb. Regarding fowl, the meaning is: You should know that they are detestable, and you should think of them as detestable. There is a bird whose name in Arabic is nesher . This is evidence, as it were, that the same bird is meant here, since the two languages are related.

the ‘ozniyya Although there is a single opinion that this bird is not found in inhabited regions [Ḥullin 62a], Sa‘adya Gaon erred by translating it into the Arabic al-‘anka . This Arabic word denotes a creature that does not exist anywhere in the world, and has never existed since Creation except as a fable — as their philologists will confirm. It is unlikely that God would forbid something that never was.

AND THESE YE SHALL HAVE IN DETESTATION AMONG THE FOWLS. Of all fowls [existent], only those mentioned expressly in this section and their species — such as those concerning which it says, after his kind, or after her kind — are prohibited, since Scripture did not mention any signs of unclean birds [by which we may know that they are] forbidden, or of clean birds [by which we may know that they are] permitted. Instead, it said, And these ye shall have in detestation among the fowls — [so that only those specifically mentioned are prohibited], and no others apart from these. Similarly, in connection with the swarming things which convey impurity, which Scripture mentioned in detail, only those mentioned by name in the section are included in that law. Our Rabbis, however, have specified certain signs [of impurity as food] in birds, so that one may recognize through them that the fowls which lack those signs are not amongst those which are prohibited [here].
Now the most important sign [of unfitness as food] in fowls is preying, for every bird of prey) interprets it as a bird of prey that kills by attacking with its claws. Further on in the text here Ramban will also elaborate on this characteristic. is invariably unfit [as food]. The Torah removed it [from us] as food, because its blood becomes heated up due to its cruelty, and is dark and thick, which gives rise to that bitter [fluid in the body] which is mostly black Note 264. and tends to make the heart cruel. There is not another fowl in the whole world that is a bird of prey apart from those mentioned in this section, and therefore one may know that any fowl which is a bird of prey, is one of those mentioned here. Thus if it is known for sure that it does not prey, it may definitely be eaten, for amongst all the forbidden fowls, there is only one which does not prey, namely the bearded vulture or the osprey, and the Sages were not concerned about it [being eaten because of reliance on the fact that it does not prey], since it is not found in habitated places, but dwells always in wilderness. Perhaps it is because it dwells in wastelands and its blood is affected for the worse by the burning heat, like that of the birds of prey, that the Torah prohibited it as food together with them.
The Sages furthermore counted amongst the signs [of fitness as food] that if a fowl be found which has an “extra” toe, and its crop and gizzard can be peeled, it is definitely fit [to be …