Laryngeal echolocation, in which calls are generated in the voice box, is absent from the family Pteropodidae. Most members of the family roost in trees where some ambient light is available. Rousettus roosts deep inside caves and tunnels, and needs a way to move in total darkness.
Its solution is click echolocation. The bat produces brief broadband clicks with the tongue, generally in pairs, at frequencies well below the ultrasonic ranges used by many microbats. The resolution is coarse compared with laryngeal systems, and it is used chiefly for orientation and obstacle avoidance rather than for catching flying prey, which Rousettus does not do.
The existence of this second, independent system is why the evolution of bat echolocation remains contested. Whether laryngeal echolocation arose once in a common ancestor and was lost in fruit bats, or arose separately in two lineages, is still argued from morphology, cochlear anatomy and genetics. Rousettus does not settle that argument, but it demonstrates that the capacity can appear more than once.