In this Mishnah, we'll talk about the Tum'ah (ritual impurity) of a Nevelah (carcass) bird. A bird that died without proper Shechitah (ritual slaughter) becomes a Nevelah and transmits Tum'ah to anybody who eats it, as opposed to the Nevelah of an animal, which transmits Tum'ah to anybody who touches it, but not to somebody who swallows it without touching it. For example, let's say a piece of a dead animal that died without proper Shechitah was forced down somebody's throat and they ate it. It didn't come in contact with the person's hands or anything on the outside of their body, so that person would not be Tameh (ritually impure). But the Nevelah of a kosher bird is the opposite: it transmits Tum'ah only when swallowed, not by being carried or touched. The Mishnah says of all the bird offerings that we spoke about in the previous two Mishnayot, “Einan metame'ot be-vet ha-beli'ah.” They do not transmit Tum'ah via Beit HaBeli'ah—the throat—which means when a person eats it, when he swallows it. Since each one of these bird offerings was killed with Melikah, and Melikah is a proper form of Shechitah when it comes to a bird, the bird is not considered to be a Nevelah. Just as with a regular animal, Shechitah prevents it from becoming a Nevelah. So if an animal is killed in that way, it wouldn't transmit the same type of Tum'ah. With the bird offering, Melikah prevents it from becoming a Nevelah. In these cases that we've been talking about, the bird offering had Melikah and therefore is fit to be eaten or burned on the Mizbe'ach (altar), and would not transmit Tum'ah. So the Mishnah here is telling us that even if the Korban (bird offering), the bird we're talking about, becomes invalid and you're not allowed to eat or burn it, in that situation it has Melikah. And therefore, it's a dead bird that was killed in a proper way, and therefore it's not a Nevelah; it does not transmit Tum'ah.
The second law we'll talk about is Me'ilah. Me'ilah is when somebody mistakenly benefits from an item that was consecrated to the Beit HaMikdash, including Korbanot (offerings). What they have to do is pay the principal plus one-fifth. They also have to bring a Korban Asham (guilt offering). The one-fifth ends up being 25% of the original value. Here we'll talk about whether these laws apply to the bird offerings that we spoke about.
A person is liable to Me'ilah if he mistakenly uses any of the bird offerings that we mentioned in the previous two Mishnayot, except in the case mentioned in the first Mishnah, where the Kohen (priest) did the blood application of the bird below the red line, like a Korban Chatat (sin offering), as he's supposed to. He also did it as he was supposed to for the Korban Chatat in every detail, and he did it Lishmah—he did it for the Korban Chatat. What we're saying here is a basic principle of Me'ilah: Me'ilah only applies when the Korban is not allowed to be consumed—eaten by anybody. All of the Korbanot that are forbidden to be eaten by anybody, either because they are invalid or because they are an Olah (burnt offering), which is fully burned on the Mizbe'ach, are the types of Korbanot to which Me'ilah would apply. But when talking about a Korban Chatat that was done properly, Me'ilah would not apply to it because it's a valid Chatat, and a Kohen is allowed to eat this type of Korban. The Torah, when it talks about Me'ilah, says it applies only to Kodshei Hashem, items that were consecrated to Hashem, which tells us that we're talking about Korbanot that are not allowed to be eaten. So an invalid bird Korban and a bird Olah are not allowed to be eaten, so Me'ilah would apply to them. But when talking about a Korban Chatat, a Kohen is allowed to eat it. What we say then is that even if a non-Kohen ate the bird Chatat, which he wasn't allowed to do, the laws of Me'ilah do not apply because the fact that it was permissible to the Kohen removes it from items that are Kodshei Hashem, that are fully consecrated to Hashem.