In Southern China, caves aren’t just used for shelter; they can be a source of revenue for the community. People have been visiting this cave for generations. The cave floor is covered in guano, so plentiful that ten minutes’ work can fill this farmer’s baskets. It’s used as a valuable source of fertilizer. A clue to the source of the guano can be heard above the noise of the river. The sound originates high up in the roof of the cave. The entrance is full of swifts.

 

 

They’re very sociable birds. More than 200,000 of them share this cave in southern Guizhou Province, the biggest swift colony in China. These days, Chinese house swifts mostly nest in the roofs of  buildings. But rock crevasses like these were their original home, long before  houses were invented.

 

 

 

Though the swifts depend on the cave for shelter, they never stray further than the limits of daylight, as their eyes can’t see in dark. However, deep inside the cavern, other creatures are better equipped for subterranean life. A colony of bats is just waking up, using ultrasonic squeaks to orientate themselves in the darkness. Night is the time to go hunting.

 

 

 

Rickett's mouse-eared bat is the only bat in Asia which specializes in catching fishes, tracking them down from the sound reflection of ripples onto water surface. This extraordinary behavior was only discovered in the last couple of years and has never been filmed before.