Why does the Torah write "Lo Ye'achlu" rather than "Lo Yochlu"?
Rashi: To implicate someone who feeds Tamei species of fish to a minor. 1
Since it means 'it shall not be eaten through you' (Rashi).
Why can we not explain that it comes to forbid deriving benefit from Tamei food (as it usually does)?
Rashi: Because the Torah writes in Devarim (14:12) "Lo Yochlu", to preclude Isur Hana'ah.
Why does the Torah list the Tamei birds (here) but the Tahor animals (in Devarim 14:4, 5)?
Rashi (Devarim 14:5): Because it always specifies the shorter list.
Ramban: It lists the Tamei birds and the eight Tamei rodents (in Pasuk 29, 30), because the list is comprehensive; it does not give Simanim. 1
The Torah lists the Tahor Behemos and Chayos in Devarim, even though it gave Simanei Kashrus, because it did not give Simanim to distinguish Chayos, whose Chelev is permitted, from Behemos, whose Chelev is forbidden. (PF)
What do all the forbidden birds have in common, that explains why the Torah forbids them specifically?
Ramban #1: Because all twenty-four birds in the list are Doreis 1 (they catch their prey and hold it down whilst they proceed to eat it alive), a clear indication that they are cruel, 2 and someone who eats them adopts their cruel nature. 3
Ramban #2 and Seforno (on Pasuk 4): Refer to 11:4:1:2.
Targum Yonasan, Chulin 3:6: All birds that do not have an extra claw and a crop, whose gizzard (stomach) cannot be (easily) peeled is forbidden. 4 Abarvenel (1) - a crop and a gizzard that can be peeled enable grinding the food later, like animals that chew the cud (refer to 11:4:1:3,4). An extra claw shows that it is not Dores (refer to 11:13:1:1).
Shlah ha'Kadosh (17, and Hagahah): An extra claw enables holding and guarding food very well. A crop and a gizzard that can be peeled show that it guards what it ate, to benefit from it. The Neshamah is weakened if the body is filthy 5 .
With the sole exception of either the Peres or the Ozniyah (two species of vulture), whose blood is nevertheless hot due to the hot climate of the areas in which it lives (Ramban).
Ramban: It is this streak of cruelty that heats their blood, which in turn, causes one who eats them to become hot-blooded and cruel. (Even though blood of all birds and animals is forbidden, the Torah permits blood that never left the flesh (Shulchan Aruch YD 67:1), or was cooked (Menachos 21a). - PF)
Ramban: Perhaps the same applies to the Tamei species of animals, since all the animals that chew their cud and possess cloven hoofs are not Dores, and all the other species tear (their prey.
See Na'ar Yonasan.
I.e. through eating birds with bad natures (PF). The Shlah adds that legs (in grasshoppers) to jump enable eating what is found on the land; others fly and destroy trees.
What is a Nesher?
Riva: It cannot be an eagle, for it says (Chulin 61a) that a Nesher does not have any Siman of Taharah, and an eagle has an Etzba Yeseirah! Ran (Chulin 20b) - Rashi says that Etzba Yeseirah is an extra toe in back. An eagle has this! Others say that it is bigger than the other toes. Ra'avad (Teshuvah 14) - it is above the others.