Swiftlet
These small birds build the nests used for bird’s nest soup in Southeast Asian caves. They navigate through absolute darkness using audible clicks produced by their syrinx. Their sounds range from 1-10 kHz, easily heard by human ears. Swiftlets fly through complex cave systems without light to reach nesting sites. Different species produce slightly different click patterns. The clicks echo off cave walls, allowing the birds to build detailed mental maps of their surroundings without using vision.