Bats on Underground River

Sabang, Palawan, Philippines. There were thousands of bats clinging on the ceiling of this cave. The cave was so dark, there's no light coming in except for our flash light. But even in the darkness, I have seen tons of bat poop or guano on the sides. I believed that the guano is a good fertilizer and can also be use for making gun powder due to the high levels of phosphorous and nitrogen.