פרשת כי תבא- Red Meat vs Poultry
Bikkurim

וְאִם־לֹ֨א קָר֥וֹב אָחִ֛יךָ אֵלֶ֖יךָ וְלֹ֣א יְדַעְתּ֑וֹ וַאֲסַפְתּוֹ֙ אֶל־תּ֣וֹךְ בֵּיתֶ֔ךָ וְהָיָ֣ה עִמְּךָ֗ עַ֣ד דְּרֹ֤שׁ אָחִ֙יךָ֙ אֹת֔וֹ וַהֲשֵׁבֹת֖וֹ לֽוֹ׃

And you shall enjoy, together with the [family of the] Levite and the stranger in your midst, all the bounty that your God יהוה has bestowed upon you and your household.
Bikkurim with Happiness

ושמחת בכל הטוב. מִכָּאן אָמְרוּ אֵין קוֹרִין מִקְרָא בִכּוּרִים אֶלָּא בִזְמַן שִׂמְחָה, מֵעֲצֶרֶת וְעַד הֶחָג, שֶׁאָדָם מְלַקֵּט תְּבוּאָתוֹ וּפֵרוֹתָיו וְיֵינוֹ וְשַׁמְנוֹ, אֲבָל מֵהֶחָג וָאֵילָךְ מֵבִיא וְאֵינוֹ קוֹרֵא (פסחים ל"ו):

ושמחת בכל הטוב AND THOU SHALT REJOICE IN EVERY GOOD THING — From this they (the Rabbis) derived the law that the recital on the occasion of bringing the first fruits is made only during the joyful period of the year — from Pentecost till the Feast of Tabernacles — when a man is gathering in his grain, his fruits, his wine and his oil; but from Tabernacles onwards until Chanucah if he brings these, he does not make the recital (Pesachim 36b).

We even bring with it specail gifts... Birds... Why?

הַגּוֹזָלוֹת שֶׁעַל גַּבֵּי הַסַּלִּים, הָיוּ עוֹלוֹת. וּמַה שֶּׁבְּיָדָם, נוֹתְנִים לַכֹּהֲנִים:

The birds [tied to] the basket were [offered] as whole burnt-offerings, and those which they held in their hands they gave to the priests.

Rambam- Nice

היו מעלים עם הבכורים להדור תורים ובני יונה מהם שהיו מביאין אותם תלויים בסלי הבכורים מהם שהיו מביאים אותם בידיהם:

The Rambam says we bring birds so it makes the Bikkurim nicer

Diffrent reason given

ושמת בטנא. ומביאין בידם תורים בני יונה, שנאמר ושמחת בכל הטוב ואין שמחה אלא בבשר.

ושמת בטנא, “and you shall place it in a basket.” The donor brings pigeons and turtle doves at the same time as a sacrificial offering seeing the Torah writes: “you shall rejoice with all the goodness” (and there is no true enjoyment unless accompanied by the eating of some kind of meat (Pessachim 109).

Or we say we bring to show happiness which is only found in meat!

Yet the Gemora says about meat from birds...

תָּנוּ רַבָּנַן: ״וְשָׂמַחְתָּ בְּחַגֶּךָ״ — לְרַבּוֹת כׇּל מִינֵי שְׂמָחוֹת לְשִׂמְחָה. מִכָּאן אָמְרוּ חֲכָמִים: יִשְׂרָאֵל יוֹצְאִין יְדֵי חוֹבָתָן בִּנְדָרִים וּנְדָבוֹת וּבְמַעְשַׂר בְּהֵמָה, וְהַכֹּהֲנִים בְּחַטָּאת וְאָשָׁם וּבִבְכוֹר, וּבְחָזֶה וָשׁוֹק. יָכוֹל אַף בָּעוֹפוֹת וּבִמְנָחוֹת — תַּלְמוּד לוֹמַר: ״וְשָׂמַחְתָּ בְּחַגֶּךָ״, מִי שֶׁחֲגִיגָה בָּאָה מֵהֶם, יָצְאוּ אֵלּוּ שֶׁאֵין חֲגִיגָה בָּאָה מֵהֶם. רַב אָשֵׁי אָמַר: מִ״וְּשָׂמַחְתָּ״ נָפְקָא. יָצְאוּ אֵלּוּ שֶׁאֵין בָּהֶן שִׂמְחָה.

§ The mishna stated that Israelites fulfill their obligation to eat peace-offerings of rejoicing with their vow offerings and gift offerings. The Sages taught that the verse: “And you shall rejoice in your feast” (Deuteronomy 16:14) comes to include all types of rejoicing as constituting a fulfillment of the mitzva of rejoicing. From here the Sages stated: Israelites fulfill their obligation to eat peace-offerings of rejoicing with their vow offerings and gift offerings and likewise with animal tithes. And the priests fulfill their obligation of rejoicing with the meat of sin-offerings and guilt-offerings, and with firstborn offerings, and with the breast and thigh of peace-offerings. One might have thought that they can fulfill their obligation even by eating bird-offerings and meal-offerings. Therefore, the verse states: “And you shall rejoice in your feast.”

This teaches that eating those animals from which the Festival peace-offering may come, i.e., sheep and cattle, is a fulfillment of the mitzva of rejoicing. This excludes these, i.e., bird-offerings and meal-offerings, from which the Festival peace-offering may not come. Rav Ashi said: There is no need to derive this halakha from “And you shall rejoice in your feast” by explaining that the word feast is referring to the Festival peace-offering. Rather, this halakha is derived simply from the phrase “And you shall rejoice.” This excludes those bird-offerings and meal-offerings that do not have an element of rejoicing, as the joy of eating is provided only by animal meat.

There is not simcha - happiness with poultry!

The Ramabam also says this

יוֹצְאִין יִשְׂרָאֵל יְדֵי חוֹבַת שַׁלְמֵי שִׂמְחָה בִּנְדָרִים וּנְדָבוֹת וּבְמַעֲשַׂר בְּהֵמָה. וְהַכֹּהֲנִים בְּחַטָּאת וּבְאָשָׁם וּבִבְכוֹר וּבְחָזֶה וְשׁוֹק. שֶׁמִּצְוָה זוֹ הִיא לִשְׂמֹחַ בַּאֲכִילַת בָּשָׂר לִפְנֵי ה' וַהֲרֵי אָכְלוּ. אֲבָל אֵין יוֹצְאִין יְדֵי חוֹבָתָן לֹא בְּעוֹפוֹת וְלֹא בִּמְנָחוֹת שֶׁאֵינָן בָּשָׂר הַמְשַׂמֵּחַ. כְּבָר בֵּאַרְנוּ בִּפְסָחִים שֶׁחֲגִיגַת אַרְבָּעָה עָשָׂר רְשׁוּת. לְפִיכָךְ אֵין אָדָם יוֹצֵא בָּהּ יְדֵי חוֹבַת חֲגִיגָה אֶלָּא יוֹצֵא בָּהּ חוֹבַת שִׂמְחָה:

Why according to Rabbinu Bachye do we bring birds if they do not bring happiness