Each evening, bats exit the cave en masse for a night of bug eating. This mass exodus is actually how the cave was discovered in 1898 by Jim White. He was riding through the desert looking for stray cattle with a fence-mending crew and saw what he thought was smoke over the next rise. Upon investigating, he realized the 'smoke' was actually bats flying out of a huge hole in the ground. He returned later with supplies and lowered himself into the cave.
The bats provided a source of income for some enterprising miners. They mined their poop - aka guano. The guano was shipped to agricultural areas and used as fertilizer. Apparently, guano is still highly sought after by organic farmers.
The park hosts bat flight programs each evening. Of course, Vol Fan and I had to attend. We had visions of bats so numerous that they did indeed look like a plume of smoke as they exited the cave......even though we had been told that the number of bats varies greatly from evening to evening. We were sure that we had picked the magical evening.
We arrived around 7:15 and walked to the bat flight amphitheater to find a seat. Due to the fact that it was a holiday weekend, the amphitheater was fairly full but we found seats easy enough. The ranger gave a very informative presentation about the cave and about the bats. She also went over the rules - Not only are photography and videography forbidden but ALL electronic devices must be powered off. As the bats exit, everyone is to be as quiet and still as possible. Easier said than done when the audience is mainly composed of families with young children.
Soon enough, the 'bat sensor' alerted us to the fact that bats were moving in the cave. Vol Fan and I were on the edge of our seats. Then the first bat. The second. We waited with baited breath - just knowing the plume was about to start billowing right before our eyes. The third. Fourth. Fifth.
And so they trickled out. A handful of bats at a time. Probably numbering several hundred in total. While still exciting and an enjoyable evening, we were a little disappointed.
We returned the next night with much lower expectations. As night began to fall, we spotted a raccoon and a ring-tail cat creeping around the rocks. Then the 'bat sensor' went off - much more active than the previous evening.
This night as the bats exited, there were groups that numbered maybe 30+ strong - in total several thousand. While still not the plume of bats we had envisioned, we were still very pleased to have been able to have this experience.