Listen to the swiftlets
The Gomantong Caves have a very large population of edible nests' swiftlets. These nocturnal birds, with a body length of 14 cm, use the caves as their breeding colonies.
An unusual ability of these birds is the use of echolocation. They emit audible calls while flying and use the calls to navigate through the caves where they live. They use a relatively crude form of echolocation compared to that of bats.
Here is a sound recording taken in The North passage of Simud Puteh.