Ibn Ezra, on Gen 1:20

“God also said: Let the waters bring forth the creeping creature having life, and the fowl that may fly over the earth under the firmament of heaven.”

“"and He said, "let swarm" - this is a transitive verb, and similar to it: "The Nile swarmed [with] frogs" Exodus 7:28. The meaning is: Let swarm the offspring with [the ability of] elevation. And what is written - that the foul will fly over the face of the firmament - is witness for [my prior] explanation of firmament. Now the Ga'on has said that "on the face of" [here] is equivalent to "with [i.e., adjoining] the face". But if so, the face of the heavens are below. The [letter] feh of ye'ofef is doubled, like the non of yechonen.”

Imported from an open dataset — not yet checked against the printed edition.