Horizontal‐Angle Resolution by Echolocating Bats

Echolocating bats were trained to discriminate between two small, spherical targets, each separated by a different angle from a third spherical target fixed in one location between the other targets. The targets were all in the horizontal plane. The angle from the fixed target to one of the movable targets was kept constant at 19° of arc, while the angle from the fixed target to the other movable target was varied from 37° to 19° in small decrements. The acuity with which the bat could use sonar to discriminate the larger angle from the smaller, constant angle of 19° was experimentally determined to be 6° to 8° for Eptesicus fuscus and 4° to 6° for Phyllostomus hastatus. Phyllostomus has a nose‐leaf through which it broadcasts its sonar cries, using a beamwidth (6 dB down) of 40° to 50° in this experimental setting. Eptesicus emits cries through its open mouth and, in the apparatus for angular discrimination, used a beamwidth of 55° to 65°. There are many other differences between these species in echoloc...