According to the Torah (Sefer Vayikra 1:14), the two types of birds that can be brought as sacrifices are torim and benei yona – turtledoves and pigeons. The tor that is referred to is identified as Streptopelia turtur, while the yona is identified as Columba livia domestica. These birds are consistently referred to differently, the former are called torim, while the latter are called benei yona. 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 yona can only be brought when it is young, before it reaches adulthood. According to the Mishna in Massekhet Ḥullin (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 yona.
The ruling of the Mishna is that torim that are too small and benei yona that have already reached adulthood cannot be brought as sacrifices and therefore performing melika on them (see Zevaḥim daf 64 for a description of melika) would not be effective in any way. Because of this a bird that was killed by means of melika 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 melika was done improperly or inappropriately, for example if melika was done with a knife rather than with the kohen’s thumbnail or if the melika was done on a non-sacrificial bird in the Temple, or a sacrificial bird outside the Temple. The Mishna teaches, however, that there are cases where the melika will not be appropriate for technical reasons, but the bird will not ritually defile someone who ate its meat, like a case where melika was done at night or where the kohen performed melika with his left hand.