According to the Torah (Sefer Vayikra 1:14), the two types of birds that can be brought as sacrifices are torim and benei yonah – turtledoves and pigeons. The tor that is referred to is identified as Streptopelia turtur, while the yonah is identified as Columba livia domestica. These birds are consistently referred to differently, the former are called torim, while the latter are called benei yonah. This is understood by the Sages to mean that a tor is only qualified to be brought as a sacrifice when it is an adult bird, while the yonah can only be brought when it is young, before it reaches adulthood. According to the Mishnah in Masechet Hullin (1:5), these two periods are mutually exclusive, and what would be an appropriate sacrifice in a pigeon would be inappropriate in a dove, and vice versa. The cut-off point between the two is just four or five days after hatching, when the bird’s body becomes covered with plumage – gold in the case of torim and yellow in the case of benei yonah.
The ruling of the Mishnah is that torim that are too small and benei yonah that have already reached adulthood cannot be brought as sacrifices and therefore performing melikah on them (see daf, or page64 for a description of melikah) would not be effective in any way. Because of this a bird that was killed by means of melikah would simply be non-kosher and would, in fact, lead someone who ate the meat of a bird that was killed this way to be ritually impure. This would also be true of other situations where melikah was done improperly or inappropriately, for example if melikah was done with a knife rather than with the kohen’s thumbnail or if the melikah was done on a non-sacrificial bird in the Temple, or a sacrificial bird outside the Temple. The Mishnah teaches, however, that there are cases where the melikah will not be appropriate for technical reasons, but the bird will not ritually defile someone who ate its meat, like a case where melikahwas done at night or where the kohen performed melikah with his left hand.