Where do the birds dwell?
Rashi: Near the springs. Radak - most birds dwell in a place of water. "Aleihem" means near, like Al means near, like "v'Alav Mate Menasheh" (Bamidbar 2:20). Also, there are birds that grow near water, for they were created from the water - "Yishretzu ha'Mayim Sheretz Nefesh Chayah v'Of Ye'ofef Al ha'Aretz" (Bereishis 1:20). Two species will multiply - one will be in the water, and one will fly on the land, and dwell also on the land.
Malbim: They dwell on the mountains, near water. "Aleihem" refers both to the mountains and the rivers. The rivers are a preparation for the dwelling of both land animals and birds.
What are "Afayim"?
Rashi: They are branches, like "v'Afye Shapir 1 " (Daniel 4:18).
Radak: They are leaves, like "Ataru Afye", "v'Afye Shapir" (Daniel 4:11, 18).
That verse (and also verse 11, which Radak cites) mentions also Anfohi (branches)! Perhaps Rashi holds that Afayim are a different kind of branches (e.g. they are thinner. - PF)
Why does the verse not mention the trees?
Radak: (This is no Chidush.) Usually there are trees on riverbanks.
What is the meaning of "Yitenu Kol"?
Radak: They chirp and sing.
