2,279. Some Birds of Questionable Status

Maachalos Assuros 1:17

The idea behind the previous halacha is that none of the prohibited species of bird that don’t attack with their claws and eat also possess one of the three signs (extra claw, crop or peelable craw) except for the bearded vulture and the osprey, which aren’t found in settled places. Rather, these are found in deserts of distant islands that are so far away, they’re at the edge of settled areas.

Maachalos Assuros 1:18

If a bird’s craw can be peeled with a knife but not by hand and it doesn’t possess any other sign, then even though it’s not a bird of prey, its status is in doubt. If the membrane was hard and tight but the craw was left in the sun so it loosened enough to be peeled by hand, the bird is permitted.