Some observe a custom of feeding birds on Shabbos Shirah. Two reasons are given for this custom. The Aruch HaShulchan (324:3) explains that since the birds sang along with the Jewish people at the splitting of the sea, we honor them by providing food on this Shabbos — the day we read about the miraculous event.
The Sefer Nimukei Orach Chaim (324:1) offers another explanation. In this week's Parsha, Moshe informed the people that manna would not fall on Shabbos. On Friday night, Dathan and Aviram scattered manna around to falsely imply that it had fallen on Shabbos in an attempt to discredit Moshe. To protect Moshe, the birds ate the scattered manna, saving him from unnecessary trouble.
This Shabbos, Parshas Beshalach, is known as Shabbos Shira (the Shabbos of Song). The Levush (685:1) explains that we call it Shabbos Shira because the Torah reading includes the song of the Jewish people, Az Yashir, which they sang after the splitting of the Sea.
In the 14th-century Sefer Minhagim of Rabbi Isaac Tyrnau, it is mentioned that a special piyyut is recited on Shabbos Shira.
Nevertheless, there are a few ways to observe this custom. One option is to place the food outside before Shabbos and feed the birds after Shabbos.
Alternatively, food could be placed outside before Shabbos and kept covered, with the cover being removed on Shabbos, this way, the food is provided on Shabbos itself. Another option is to brush off crumbs from the meal so the birds can eat them.
However, many authorities have raised objections to the custom. Among those who disagree are the Magen Avraham (324:7), Elya Rabbah (324:12), Baal HaTanya (324:8), and the Mishnah Berurah (324:31), among others. Their objection is based on the prohibition in the Shulchan Aruch (324:11), which forbids feeding animals on Shabbos that do not rely on humans for food.