"And let birds fly" (Genesis 1:20). It is the way of the world that a king of flesh and blood builds a palace and settles dwellers in the upper stories and in the lower stories, but can he settle them in the open air? Yet the Holy One, blessed be He, settles dwellers in the open air, as it is said, "And let birds fly."
How the Holy One Settles Living Things in Empty Air
Yalkut Shimoni on Torah 12:1
וְעוֹף יְעוֹפֵף, בְּנֹהַג שֶׁבָּעוֹלָם מֶלֶךְ בָּשָר וָדָם בּוֹנֶה פְּלָטִין מַשְׁרֶה דִּיּוּרִין בָּעֶלְיוֹנִים וּבַתַּחְתּוֹנִים, שֶׁמָּא בֶּחָלָל אֲבָל הַקָּדוֹשׁ בָּרוּךְ הוּא מַשְׁרֶה דִּיּוּרִין בֶּחָלָל, שֶׁנֶּאֱמַר וְעוֹף יְעוֹפֵף.