Mishnah Taharos 1:3: The carcass of an impure fowl requires thought [one must initially think to use it for food] and being primed [for impurity, by becoming wet]; and it renders foods impure when it has [at least the volume] equivalent to an egg, and [at least the volume] equivalent to half a loaf invalidates one's body [from eating terumah by rendering him impure]; and it does not have [the law of rendering one impure] when it is being swallowed when it has [at least the volume] equivalent to an olive; and one who eats it does not require [waiting until] sunset [on the day of his immersion before he becomes pure again]; and one is not liable for entering the temple [while impure] because of it; but terumah is burned on its account [i.e. one rendered impure by it renders terumah impure]; and one who eats a limb taken from it while alive does not endure the forty [lashes]; and slaughtering it does not purify it. The wings and feathers can be rendered impure, and can render impure, and are added together. The beak and the talons can be rendered impure, can render impure, and are added together.

נִבְלַת הָעוֹף הַטָּמֵא צְרִיכָה מַחֲשָׁבָה וְהֶכְשֵׁר, וּמְטַמְּאָה טֻמְאַת אֳכָלִין בְּכַבֵּיצָה, וְכַחֲצִי פְרָס לִפְסֹל אֶת הַגְּוִיָּה, וְאֵין בָּהּ כַּזַּיִת בְּבֵית הַבְּלִיעָה, וְהָאוֹכְלָהּ אֵין טָעוּן הֶעֱרֵב שֶׁמֶשׁ, וְאֵין חַיָּבִין עָלֶיהָ עַל בִּיאַת מִקְדָּשׁ. אֲבָל שׂוֹרְפִין עָלֶיהָ אֶת הַתְּרוּמָה, וְהָאוֹכֵל אֵבָר מִן הַחַי מִמֶּנָּה אֵינוֹ סוֹפֵג אֶת הָאַרְבָּעִים, וְאֵין שְׁחִיטָתָהּ מְטַהֲרְ תָּהּ. הַכְּנָפַיִם וְהַנּוֹצָה, מִטַּמְּאוֹת וּמְטַמְּאוֹת וּמִצְטָרְפוֹת. הַחַרְטוֹם וְהַצִּפָּרְנַיִם, מִטַּמְּאִין וּמְטַמְּאִים וּמִצְטָרְפִין:

Mishnah Taharos 1:4: And regarding an animal: the hide, the sauces [in which it is cooked], the seasonings, the meat stuck to the hide, the bones, the sinews, the horns, and the hooves combine to render impure with the impurity of foods, but not with the impurity of carcasses. Similarly, one who slaughters an impure animal for a gentile and it is still twitching, it can render impure with the impurity of foods, but not with the impurity of carcasses until it dies or until its head is chopped off. The rendering of the impurity of foods was made more numerous than the rendering of the impurity of carcasses.

וּבַבְּהֵמָה, הָעוֹר וְהָרֹטֶב וְהַקִּפָּה וְהָאֲלָל וְהָעֲצָמוֹת וְהַגִּידִים וְהַקַּרְנַיִם וְהַטְּלָפַיִם, מִצְטָרְפִין לְטַמֵּא טֻמְאַת אֳכָלִין, אֲבָל לֹא טֻמְאַת נְבֵלוֹת. כַּיּוֹצֵא בוֹ, הַשּׁוֹחֵט בְּהֵמָה טְמֵאָה לְנָכְרִי וְהִיא מְפַרְכֶּסֶת, מְטַמְּאָה טֻמְאַת אֳכָלִין, אֲבָל לֹא טֻמְאַת נְבֵלוֹת, עַד שֶׁתָּמוּת אוֹ עַד שֶׁיַּתִּיז אֶת רֹאשָׁהּ. רִבָּה לְטַמֵּא טֻמְאַת אֳכָלִין, מִמַּה שֶּׁרִבָּה לְטַמֵּא טֻמְאַת נְבֵלוֹת: