Augustine of Hippo

Then the Psalm goes on in its text, "Upon them the fowls of the heaven shall inhabit" [Psalm 104:12]. ...Upon the mountains, then, the fowls of the air shall have their habitation. We see these birds dwell upon the mountains, but many of them dwell in plains, many in valleys, many in groves, many in gardens, not all upon mountains. There are some fowls that dwell not save on the mountains. Some spiritual souls doth this name denote. Fowls are spiritual hearts, which enjoy the free air. …

Exposition on Psalm 104 ↗

Jerome

Over them the birds of heaven shall dwell. Remember the parable of the mustard seed, and the birds that dwell in it. From the midst of the rocks they shall give voice. Each thing in its own tongue praises the Lord. In the Hebrew it has "of the trees."

Homily 30, on Psalm 103 ↗

Bonaventure

From the midst of the rocks they shall give forth their voices. That is, from the midst of the two cherubim of which the Lord speaks, meaning from the space between them, that is, from the midst of the Two Testaments. The third firmness of faith consists in the full accord of the witnesses, and is found in three things: in the words of Scriptures, in the decrees of the councils, and in the writings of the saints.

Collations on the Hexaemeron, Collation 9 ↗