Swiftlets of the genus Aerodramus produce rapid double clicks, generally in the low kilohertz range, and use the returning echoes to place themselves relative to cave walls and nest ledges. Oilbirds do something similar. Both are the exceptions among birds, which otherwise navigate by sight.
The resolution is much lower than a bat's. Experiments indicate swiftlets detect obstacles on the scale of centimetres rather than the fine detail bats resolve with ultrasonic calls, which is enough for gross orientation in a dark cave but not for catching insects. Swiftlets hunt by sight in daylight outside the cave.
The nests, built from a bird's own hardened saliva, are harvested for soup and are among the most valuable animal products by weight. Sustainable harvest regimes are contested, and species limits within Aerodramus are still being revised, so figures attributed to a single species should be read with care.