Twenty million bats spend their summers in BCI's Bracken Bat Cave near San Antonio, Texas. They delight BCI members who accept their invitation to see the bats emerge in the evenings to eat about 200 tons of insects a night. They also leave an enormous amount of nutrient-rich droppings on the floor of the cave.
The bat guano, up to 30 feet high in places, has supported a mining industry for fertilizer since the 1850s. And it still does, although at a much smaller and more technological level than in the past, according to the San Antonio Express-News.
Robert Sloan, the newspaper reports, is one of five crewmembers who use a large suction hose to remove guano from the mine floor. They go to work at Bracken every other year and only during the winter months, after the Mexican free-tailed bats have migrated south to Mexico for the winter.
“It's not as bad as it sounds,” Sloan told the Express-News. “You get used to it. You can work in it. As a matter of fact, [inside the cave] is a pretty cool place to work.”
Contractor Garden-Ville plans to remove about 200 tons of guano during the four weeks they have access to the cave, and that's a small fraction of what lies on the cave floor.
“It's really not bat guano,” said Malcolm Beck, a consultant to Garden-Ville. “It's really beetle poop. The insects eat the plants, the bats eat the insects and beetles eat the guano. It goes through several stages. It's more processed than regular fertilizer. I think it refines it.”
BCI Conservation Program Administrator Andy Moore said the mining does not harm the bats and “actually creates more roosting space.” And Bat Conservation International, which owns and protects the cave, receives $125 a ton, plus 25 cents a bag to help pay for its bat conservation programs.
The mining operation uses a huge vacuum, attached to about 800 feet of tubing, to suck the guano from the cavern floor up into big 16-cubic-yard roll-off containers. The containers are then taken to Garden-Ville, where the guano is sifted and put in bags ranging from three quarts to a ton.
The guano itself is rather benign, the newspaper says. By the time the colony has left for the year and the beetles have done their work and gone into hibernation, what remains is a dry, powdery and earth-toned substance with the odor of ammonia.
