How does echolocation help swiftlets fly in caves?

Certain species of swiftlets use echolocation to navigate and orient themselves within the dark caverns they inhabit. This biological sonar allows them to avoid obstacles and move safely through environments where visual cues are unavailable.123

The mechanism functions through the emission of clicking sounds at frequencies ranging from 1,500 to 5,500 hertz. These pulses, which are audible to the human ear, are typically emitted at a rate of about six per second. By listening to the echoes that reflect back from the cave walls and other objects, the birds can effectively map their surroundings and maintain flight paths in total darkness. This capability is a rare trait among birds, shared primarily with the oilbird.12