Hendrickson 1950 Pipistrellus hesperus Aug. 28 Lower Covington Plate, 5000 ft., Riverside Co., Calif. Watched several individuals working the area near the waterhole in the canyon simply emptying into the first wash S. of camp. Many horses. They were flying in full morning sunlight, at about 7:00 when I arrived, and were last noted at about 9:45, when I left. Many times individuals flew to within a few feet of where I was sitting in a niche in the sloping canyon wall about 20 ft. above the canyon floor. One was seen catching a muscid fly which was noted before the bat appeared in my field of vision. Several times bats caught insects and flew toward me, "cleaning" on them with seemingly exaggerated chewing jaw movements. A difference was noted in the sound made by their wings as they flew close to me. One was identifiable by a sound considerably higher than the others (hole or tear in wing?). At 8:00 a bat which happened to be under direct scrutiny at the moment was seen to fly directly at the canyon wall opposite me, and to