Continuing the discussion of designating pigeons on Yom Tov, where we learned that according to Beis Hillel a person must identify while it is still daytime which pigeons he intends to take so that he may slaughter them on Yom Tov, our Mishnah now spells out the practical laws of that identification.
The text of the Mishnah:
"Ziman shechorim u'matza levanim, levanim u'matza shechorim, shnayim u'matza sheloshah - asurim" - he designated black pigeons and found white ones, or he designated white ones and found black ones, or he designated two pigeons and found three: they are all forbidden.
At first glance, what is the novelty in ruling that one who designated black pigeons and found white ones may not use them? It is obvious that these are not the ones he prepared.
From this the Gemara establishes that the case is one in which he prepared both black and white pigeons, in two separate places, and the next day he found the black ones in the place of the white ones and the white ones in the place of the black ones. Although one might have attributed this to the pigeons having switched places, so that these are the very ones that were prepared, the Mishnah teaches that we do not say so: just as one who prepares two and finds three certainly did not include the third in his designation and it came from elsewhere, so too here, when they are found out of their places, we must assume that these are other pigeons that were never designated, and it is forbidden to slaughter them on Yom Tov.
"Sheloshah u'matza shnayim - mutarin" - he designated three pigeons and the next day found only two: they are permitted, since we may attribute the discrepancy to one of them having flown away from the nest.
"B'soch hakein u'matza lifnei hakein - asurin; v'im ein sham ela heim, harei eilu mutarin" - he designated them inside the dovecote, in their resting place, and found them in front of the nest rather than in their exact spot: they are forbidden, for we must assume that these are not the ones designated but others. But if there are no other pigeons in the area besides these, we may attribute them to the designation, and they are permitted.
The Gemara's explanation of this case:
The case involves young fledglings that are not yet able to fly, but only walk on their feet. Therefore, if there is no other dovecote within fifty amos - the usual distance such fledglings walk - and he designated them inside the nest and found them in front of it, one may attribute them to the designation, since there is no other nest within their walking range.
The Gemara adds: even if there is another dovecote within fifty amos, but it is around a corner, such that had the fledglings come out of it they would have lost sight of the nest from which they emerged, they are still permitted. For young fledglings never venture beyond the range of sight of the nest they came from, and they will not risk such a walk. Consequently we must assume that they did not come from that dovecote, but from the nest that was designated, and they are permitted on Yom Tov.
In summary: Our Mishnah teaches that the identification must be certain: if he designated black ones and found white ones, or designated both groups and found them with their places reversed, and likewise if he designated two and found three - they are all forbidden. If he designated three and found two - they are permitted, since we attribute the discrepancy to one having flown off. If he designated them inside the nest and found them in front of the nest - they are forbidden, unless there are no other pigeons there. And according to the Gemara's explanation: when dealing with young fledglings that cannot fly, we attribute them to not having come from another dovecote - both when there is no other dovecote within fifty amos, and when the other dovecote is situated in a place such that walking from it would have taken them out of sight of their nest.