John Gill Commentary Genesis 7:3

"of the birds also of the heavens, seven and seven, male and female, to keep seed alive upon the face of all the earth." — Genesis 7:3 (ASV)

Of fowls also of the air by sevens, the male and his
female
That is, of such as were clean; seven couple of these were to be brought into the ark, for the like use as of the clean beasts, and those under the law; and so at this time, and here meant were turtledoves, and young pigeons that were for sacrifice; and the rest were for food: and the design of bringing both into the ark was, to keep seed alive upon the face of all the earth ;
that the species of creatures might be continued, both of beasts and birds, clean and unclean.