The ability of a single individual Rousettus aegypticus to avoid small wires by echolocation was compared with previous measurements of obstacle avoidance in Myotis lucifugus. Both species avoided 3-5 millimeter wires in about 85% of the flights through a row of vertical wires spaced somewhat more than one wingspread apart (30 cm spacing for Myotis and 53 cm for Rousettus). The obstacle avoidance score of the Rousettus fell gradually to 68% misses at a wire diameter of 1.07 mm, 58% at 0.65 mm, 45% at 0.46 mm and 18% at 0.28 mm. This is only slightly inferior to the acuity of echolocation of Myotis, which have serious difficulty dodging wires smaller than about 0.25 mm, despite the fact that the orientation sounds of Rousettus are clearly audible clicks. Unlike Myotis this Rousettus was seriously disoriented by intense thermal noise, even when this consisted primarily of frequencies above 20 kc.