Why no avian husbandry and wifery?

Summary: Bringing to the fore the Tur's explanation of this deviation, of ish veIshto being used for animals but not for birds, in terms of creatures brought onto the teiva.

Post: As part of a previous post, I shared my guess as to why there was a sudden deviation from zachar unekeivah, "male and female", for the seven pairs of kosher animals and two pairs of non-kosher animals brought onto Noah's ark.

That is, contrast these two pesukim in parashat Noach:

2. Of all the clean animals you shall take for yourself seven pairs, a male and its mate, and of the animals that are not clean, two, a male and its mate.		ב. מִכֹּל הַבְּהֵמָה הַטְּהוֹרָה תִּקַּח לְךָ שִׁבְעָה שִׁבְעָה אִישׁ וְאִשְׁתּוֹ וּמִן הַבְּהֵמָה אֲשֶׁר לֹא טְהֹרָה הִוא שְׁנַיִם אִישׁ וְאִשְׁתּוֹ:
3. Also, of the fowl of the heavens, seven pairs, male and female, to keep seed alive on the face of the earth.		ג. גַּם מֵעוֹף הַשָּׁמַיִם שִׁבְעָה שִׁבְעָה זָכָר וּנְקֵבָה לְחַיּוֹת זֶרַע עַל פְּנֵי כָל הָאָרֶץ:

As I wrote there,

Why use the idiom of ish veIshto precisely here, and not elsewhere? Because here is where we hear about bringing seven and bringing two. We might think that this meant a total of seven of each kosher species, some of which were male and some female, and a total of two of each non-kosher species, one male and one female. By specifying ish veIshto, it becomes clear that we are speaking of seven sets and two sets, respectively. (Rashi says otherwise. See 6:19.)

In a comment on that post, Reb Chaim HaQoton brought my attention to the Tur, who offers a different explanation:

בבהמה כתיב שבעה שבעת איש
ואשתו ובעופות כתיב זכר ונקבה לפי שהבהמות
נרבעין אמר אותן שדבקו זה בזה איש ואשתו
ולא נרבעו אבל עופות דלא שייך בהו רביעה
אמר זכר ונקבה

This would account for the switch between beheimot on the one hand and ofot on the other. Thus, this would account for these two pesukim. However, zachar unekeivah actually occurs consistently throughout the entire narrative. Thus, in perek 6:

19. And of all living things of all flesh, two of each you shall bring into the ark to preserve alive with you; they shall be male and female.

יט. וּמִכָּל הָחַי מִכָּל בָּשָׂר שְׁנַיִם מִכֹּל תָּבִיא אֶל הַתֵּבָה לְהַחֲיֹת אִתָּךְ זָכָר וּנְקֵבָה יִהְיוּ:

And in perek 7:

3. Also, of the fowl of the heavens, seven pairs, male and female, to keep seed alive on the face of the earth.

ג. גַּם מֵעוֹף הַשָּׁמַיִם שִׁבְעָה שִׁבְעָה זָכָר וּנְקֵבָה לְחַיּוֹת זֶרַע עַל פְּנֵי כָל הָאָרֶץ:

and

8. Of the clean beasts and of the beasts that are not clean, and of the fowl, and all that creeps upon the earth.		ח. מִן הַבְּהֵמָה הַטְּהוֹרָה וּמִן הַבְּהֵמָה אֲשֶׁר אֵינֶנָּה טְהֹרָה וּמִן הָעוֹף וְכֹל אֲשֶׁר רֹמֵשׂ עַל הָאֲדָמָה:
9. Two by two they came to Noah to the ark, male and female, as God had commanded Noah.		ט. שְׁנַיִם שְׁנַיִם בָּאוּ אֶל נֹחַ אֶל הַתֵּבָה זָכָר וּנְקֵבָה כַּאֲשֶׁר צִוָּה אֱ־לֹהִים אֶת נֹחַ:

and

16. And those who came male and female of all flesh came, as God had commanded him, and the Lord shut him in.

טז. וְהַבָּאִים זָכָר וּנְקֵבָה מִכָּל בָּשָׂר בָּאוּ כַּאֲשֶׁר צִוָּה אֹתוֹ אֱ־לֹהִים וַיִּסְגֹּר יְ־הֹוָ־ה בַּעֲדוֹ:

Meanwhile, this expression of איש ואשתו occurs a sum total of once. The impression one gets is that זכר ונקבה is the standard, while  איש ואשתו is a diversion from the standard for some purpose. Which is why I like my own peshat better.

To answer on behalf of the Baal HaTurim, though, if we examine each of the examples I cited above, they are each inclusive of both beast and fowl. Therefore, one can offer that ish veIshto was not available in any of these cases.

What does the Baal HaTurim mean that לא שייך בהו רביעה regarding birds? See here, about avian reproduction. Male birds, for the most part, lack a penis. (There are exceptions. The testes are internal, and the sperm is in the male's cloaca. The sperm is transferred to the female bird by a 'cloacal kiss', in which the two cloacas are placed against one another. Lacking any external sex organs, and given that this act does not involve penetration, he is absolutely right (again, for most birds), that לא שייך בהו רביעה, such that we would not necessarily refer to ish veIshto.