So many Mexican free-tail bats fly out of the Bracken Bat Cave on a summer evening that their spiral path creates a vortex of rising air that helps lift the bats, drawing out even more.In a few hours, 20 million emerge from the home of the largest concentration of mammals in the world, according to Bat Conservation International, which owns the cave and the surrounding 697 acres next to Natural Bridge Caverns.
Out of the cave, they form an aerial river that veers back and forth a few feet above the treetops in search of thermals to lift them higher.
Ultimately, they fly as far as 60 to 100 miles from the cave in search of insects.
For the first time Saturday, BCI opened the cave to the public to mark International Bat Night. In partnership with Natural Bridge Caverns, 10 more public viewings are scheduled for later this summer and early fall.
“I've never seen anything like this before,” said Wyatt Prappas, 10, who came with his family from Houston. “This is spectacular.”
Until now, only members of the nonprofit or those invited on VIP tours could watch the bats leaving the cave in the evening or returning in the morning, said James Eggers, director of education for BCI.
But because next year has been declared by the United Nations as the year of the bat, the group wanted to do more public outreach.
Plus, this year's drought has made for some of the best bat viewing in decades, Eggers said. With fewer insects in the air, the bats are forced to spend more time hunting, which means leaving the cave before nightfall.
During last year's wet summer, the bats were emerging just as the sun was setting. This summer they are taking wing an hour or two before dark, said Fran Hutchins, BCI's Bracken Cave coordinator.
Along with giving visitors more light to see the bats, predators are taking advantage of the early exit.
On Saturday a red tail hawk swooped into the middle of the swarm of bats, turned upside down and crushed one in its talons. A Cooper's hawk was next, plucking its dinner while swooping in from above.
Hutchins said he counted 25 migrating Cooper's hawks Friday night.
The bats themselves must eat the equivalent of their own body weight every day before they head to Mexico for the winter. The colony consumes some 200 tons of bugs each night.
Hutchins explained how the cave makes an ideal nursery. The bats have lived in it for at least 5,000 years, and the floor is covered with more than 60 feet of bat guano.
High in nitrogen, the bat droppings were used to make gunpowder during the Civil War, and the cave entrance was protected by Texas solders. Their barracks are still standing.
Today, the guano is mined every other year during the winter by vacuums and sold as a natural fertilizer.
During the summer the heat from the composting guano raises the temperature at the cave's ceiling to 102-104 degrees, helping the infant bats stay warm and dedicate all their energy to growing.
In eight weeks they can fly and fend for themselves, Hutchins said.
“This is why they love this cave,” he said.
At maturity, the bats will weigh as much as two quarters, and when they emerge from the cave any slight breeze will push them sideways into the walls and surrounding trees.
When the bats are pushed over the spectators, who are asked to stand and sit quietly at the edge of the limestone sinkhole, the thousands of wings fluttering overhead sound like a distant waterfall.
Wyatt stood in amazement of it all and kept a close eye on snakes that were waiting near the bottom of the sinkhole for their chance to pounce.
After more than an hour of watching the bats emerge he was still captivated by the spiraling mass.
“I thought it would end way before this,” he said, before going back to see if the snake would strike.
Source: San Antonio News