The answer is quite clear in the Bible.
And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven. (Gen 1:20) God had already divided the waters, so these "waters" were the seas. Therefore this may be seen as miraculous, since birds are so different from marine creatures.
Thanks Nehemiah6 for posting Gen 1:20.
"And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl
that may fly above the earth in the open firmament of heaven."
'Waters' in the Bible can refer to God's word (Ephesian 5:26) and to people who are of the word. So, we might say that his word brings forth abundantly. Especially since God gives to the true believer life and that life more abundantly. We see in Gen 1:20 that the word (waters) bring forth creatures having life and this is abundantly. This is a picture of how the word of God produces believers who have the life of God, his spirit, his salvation. They are the creatures God's word creates. The waters brings forth life creatures - true believers. Further, we see that the word produces
birds in the open heaven. This is interesting because we find that the Bible speaks of believers seeing heaven open. When heaven is open in Bible language it means that a person is able to receive the gospel. Indeed, those who are born again have the door (Jesus) open and are part of the open field of harvest. If the firmament of heaven were closed in Gen 1:20 the picture would not be pointing to true believers. We see in the Bible in the parable of the mustard seed that believers are spoken of as
birds of the air. The mustard seed was tiny but grew into a mighty plant in which the birds of the air lodged. We learn that that is a parable of the kingdom of heaven, so the birds of the air are a picture of those in the kingdom of heaven, in simple words true believers.
Rather than always expecting a surface translation of Genesis, consider that the Bible is written by God in parable form. "Give ear, O my people,
to my law: incline your ears to the words of my mouth. I will open my mouth in a parable"
"But without a parable spake he not unto them"