The sprigs and branches being cut down and thrown upon the ground, with the unripe grapes upon them, they shall lie upon the earth neglected by men, as being unripe, and unfit for their use, so that either birds or beasts may shelter themselves with them, or feed on them, both summer and winter. You are not to understand that the summer is appropriated to the fowls, and the winter to the beasts; but this is only an elegancy of the Hebrew language to use such distributions, of which we have many instances in prophetical writings.
Related Commentaries of Isaiah 18:6
Isaiah 18:6
6 They shall be left together unto the fowls of the mountains, and to the beasts of the earth: and the fowls shall summer upon them, and all the beasts of the earth shall winter upon them.