However, we can formulate some logical rules, even if we don't know the exact physical birds they refer to. Twenty of the non-kosher birds possess all three kosher signs, that is, extra toe, crop, and gizzard that can be peeled - but they claw their prey. The raven has two of the kosher signs. The ossifrage and the osprey have one kosher sign, a different one each. An eagle has no kosher signs. To determine if a bird is kosher it is first compared to the eagle. If it is unlike an eagle and has at least one kosher sign, and it does not belong to the other twenty-three non-kosher types, then it is kosher.
Ameimar formulated a rule: even if one is not expert in identifying an ossifrage and an osprey - which are rare - if he sees a bird with one kosher sign, it is kosher, provided that it does not claw.
Art: Herbert William Weekes - The Sermon - A Raven Addressing a Gaggle of Geese