Nice video and report, too. A few of us visited Bracken years ago and the sight of all those bats on the walls and ceiling is amazing. You can't go too far into the cave due to the levels of ammonia in the air from the urine and bat guano. The floor literally is alive with movement of beetles, worms, etc. When you glanced up at the bats you could feel the fine spray of urine on your face.
Workers used to use breathing apparatus to enable them to breathe to mine the guano from further back in the cave.