Hullin, Chapter Six, Mishnah Four
1) If a person slaughtered a hundred wild animals in one place, one covering suffices for all.
a) If [he slaughtered] a hundred birds in one place, one covering suffices for all.
2) If [he slaughtered] a wild animal and a bird in one place, one covering suffices for both.
a) Rabbi Judah says: if he slaughtered a wild animal he should cover up its blood and then slaughter the bird [and cover it up also].
3) If a person slaughtered and did not cover up the blood and another person saw it, the other must cover it up.
4) If he covered it up and it became uncovered, he need not cover it up again.
5) If the wind covered it up, he must cover it up again.
Section one: If one slaughters multiple animals of the same type, he is liable to cover up the blood only once. He need not cover up the blood for each animal individually.
Section two: According to the first opinion, the same applies to slaughtering wild animals and birds. All of the blood from both types can be covered together.
Rabbi Judah disagrees, and says that if there are two different types that require the covering of blood, birds and wild animals, then the blood of each must be covered up separately. He would agree, though, that one can cover up all of the birds blood at one time and all of the animals blood at one time.
Section three: The mitzvah of covering the blood of a slaughtered bird or wild animal is incumbent upon everyone, not just the person who slaughtered the animal. Therefore, if someone sees it, he must cover it up.
Section four: Once the mitzvah has been fulfilled, if the blood becomes uncovered, it need not be fulfilled again. In other words, the mitzvah is to cover the blood and not to make sure that the blood is covered.
Section five: The Talmud explains that after the wind covers the blood it becomes uncovered. Since no one actually fulfilled the mitzvah, if it becomes uncovered again, he must cover it up.