Albert Barnes Commentary Job 39:8

"The range of the mountains is his pasture, And he searcheth after every green thing." — Job 39:8 (ASV)

The range of the mountains is his pasture - The word rendered “range,” יתור yâthûr — means properly a “searching out,” and then that which is obtained by search. The word “range” expresses the idea with sufficient exactness.

The usual range of the wild ass is the mountains. Pallas, who has given a full description of the habits of the Onager, or wild ass, states that it especially loves desolate hills as its abode. “Acts of the Society of Sciences of Petersburg,” for the year 1777.