Halakha Ulangan 14:15: Torat HaBayit HaKatzar & Mishneh Torah, Forbidden Foods

Signs for the birds were not explained in Scripture. However the Sages said that any bird that claws [its prey] alive and eats it alive is known to be impure. And any bird that has an extra digit and its gizzard can be peeled by hand, even after it is placed in the sun, is permissible; it is known that it does not prey. If it can be peeled with a knife, but not by hand, there is a doubt regarding it being in the category of peeled. [Regarding] other birds that come with some of these signs, some of them are permissible and some of them are forbidden. Hence we only eat [them] based on tradition. If they were eaten in some places, but not eaten in [other] places, it appears to me that we rely on those places where its permissibility spread. For had they not received this from their early fathers who were experts, they would not have treated them as permissible. And even though some places did not receive this, we do not say to the one who did not see the novelty, "Come and testify," but rather to the one who did see the novelty. And it is possible that I may say to the ones that treated them [as forbidden, that] they are permissible but they treated them as forbidden on account of impure birds that were similar to them found in those places. Some of the Geonim, may their memory be blessed, instructed [about] all birds that have a wide beak and the palm of its foot like that of a goose, it is certain that it does not prey. For this is what they received from the earlier elders. A swallow that lives in a house, if its belly is white, it is permissible; but, if not, it is forbidden. And in these places, we have not seen anyone who treats them as permissible, even if their belly is white. The egg of an impure bird is forbidden, as it is stated (Deuteronomy 14:15), "And the daughter of the yaanah." But the yaanah does not have a daughter (whose forbidden status would be different from that of its mother). Rather, this daughter is its egg.

Milch und Eier
Alles nur irgend Genießbare, das von diesen, unter Strafe der Geißelung verbotenen Gegenständen herrührt, ist laut Vorschrift der Tora, ebenfalls zu essen verboten, wie z. B. die Milch von unreinen Haus- und wilden Tieren, die Eier des unreinen Vogels und der Rogen unreiner Fische, denn es heisst in der Schrift: »Und das Junge des Straußes«, was auch auf dessen Ei hindeutet. Dieses Verbot erstreckt sich nun auf alle, gleich dem Strauße, verbotenen Tiere, wie auch auf Alles, das gleich dem Ei, von etwas Verbotenem herrührt.