Echolocation is a poor tool for finding a motionless moth on a leaf, because the echo from the prey is buried in the echo from the leaf. Gleaning bats therefore lean on other senses, and Macrotus californicus leans on vision more than most.
The species has enlarged eyes and forages by slow, manoeuvrable flight close to vegetation and the ground, taking large moths, grasshoppers, beetles and caterpillars. Laboratory work has shown individuals locating and capturing prey under dim illumination with little or no echolocation, and struggling in complete darkness with visual cues removed. Its echolocation calls are also low in intensity, in keeping with a whispering gleaner.
The roost requirement is the species' practical constraint. It does not hibernate and does not migrate far, so it needs roosts warm enough to sit out desert winters, which in most of its United States range means abandoned mines. Mine closures for public safety have removed roosts, and gated closures that allow bat passage are the standard remedy where the roost is known.