The structure of the calls made by the echolocating fruit bat Rousettus aegyptiacus while flying within a flight tunnel were investigated. Calls are impulsive clicks lasting around 250 μs, with most energy occurring during the first 100 μs. Such a call duration is much shorter than that previously reported for this species. The ability of R. aegyptiacus to detect and avoid obstacles was tested in both the light and total darkness. Bats were able to detect and avoid 6 mm diameter wires significantly more often than 1.3 mm diameter wires when tested in the light. In the dark, the same relationship held, with no decrease in the ability to detect and avoid the obstacles. Bats used echolocation in both the light and the dark conditions. The simple impulsive clicks used in echolocation by this species are thus able to detect wires of at least 6 mm in diameter and probably smaller. The detection problems associated with very short duration signals is discussed. The possession of both a good visual system, and a good echolocation system in this species has implications for the evolution of echolocation in bats.