2,280. Birds of a Feather

Maachalos Assuros 1:19

The Geonim said they have a tradition not to permit a bird that possesses only one of the aforementioned signs except for the sign of a craw that can be peeled by hand. If it can’t be peeled by hand, it was never permitted even if it has a crop or an extra claw.

Maachalos Assuros 1:20

If a bird divides its claws on a wire, placing two on one side and two on the other, or if it seizes something in the air and eats it while still in the air, then it’s a bird of prey and not kosher. Any species of bird that lives with and resembles non-kosher species is also a non-kosher species.