We feed birds on Shabbat Shirah to say that if the Jewish people, compared to a bird, will devote themselves, then God will provide them food without toil.
So we shake out our tablecloth, provided there is an eruv, and thereby allow the birds to share our Shabbat feast!
REMEMBER THE JOY OF SHIRAT HA YAM!
Hear the ba'alei ha shirbecause they rule the air, and music is created by the flow of air.
"And behold on the seventh day some of the people went out to gather [manna] and did not find any". Why does it say "and did not find any"? Because Datan and Aviram went out on Friday night outside the camp and spread some manna, in order to make Moshe a liar, since he said there would be no manna on Shabbat. They then said to the people: go out and see that there is manna in the fields! Therefore, some people went out to gather, but found nothing because the birds had eaten the manna which Datan and Aviram had strewn about. We give them their reward on Shabbat Shirah since we also read the story of the manna on that day.