Not really a cave, this was actually taken at an old Spanish fortress in Brazil on a river boarder with Bolivia. The walls were alive with the chirps of bats. There must have been millions of them, every crack was filled with them.
I haven’t identified what kind of bat this is yet so any ID help is welcome.
Nikon D80 Tamron 70-300mm 1/125s f/5.6 ISO 100 Flash SB-600 June 2011