Valley of the Bats: Mexican free-tailed bats are the summer show in northwest Oklahoma
Melynda Hickman, the wildlife diversity biologist for the Oklahoma Department of Wildlife Conservation, describes the nightly summer exodus of hundreds of thousands of bats from the Selman Bat Cave as a "river of bats."
The bats exit from the cave, which is tucked in the gypsum bluffs that tower the sandsage prairie, flying in such a tightly organized group that it does look like a river of bats.
But it sounds more like an ocean. When thousands of bats were approaching and then flying above my head, it sounded like the waves rolling from the ocean onto the shore.
This summer spectacle in northwest Oklahoma has been going on for more than a century. Migrating Mexican free-tail bats use the cave not far from Alabaster Caverns State Park as a maternity roost during the summer.
They winter in Mexico, but start migrating north in February. The Selman Bat Cave near Freedom is one of four maternity caves in western Oklahoma that the pregnant female bats find suitable to give birth to their pups in the summer.
"The females are very picky about where they are going to raise their pups," Hickman said. "The cave has to have a certain size, a certain entrance. That's why there are only four in Oklahoma that meet that criteria."
The number of female bats that use the Selman Bat Cave as a maternity cave is estimated at half a million. Each bat gives birth to one pup, meaning before the summer ends there could be as many as 1 million bats in the cave.
Shortly before dusk each night, the bats leave the cave to begin their all-night hunt for insects. The mama bats go first, and begin the exodus as an organized group to conserve energy, Hickman said.
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Like swimmers using a breast stroke to speed through the water, the bats do something similar in the sky.
"They are using the lift off of each other's wind that is created in that organized stream," Hickman said. "Their goal is to get far away from the area to hunt insects."
Because of Doppler radar, the Wildlife Department biologists know that the bats from the Selman Bat Cave will travel as much as 60 miles in either direction to hunt insects before returning. Mexican free-tailed bats, unlike big brown bats, are hunting too high to eat mosquitoes.
They often dine on beetles, flying ants and moths, sometimes flying as high as 10,000 feet on their hunts, but generally hunt from 50 to 100 feet above the ground, Hickman said.
The bats eat so many insects during the summer that it's been estimated to save farmers in Woodward County $8.7 million per year by not having to spend money on pesticide control for insects, according to the U.S. Department of Agriculture.
The female bats travel miles away to hunt so their young, who are still learning to fly, can forage closer to the cave.
It takes more than an hour for all of the bats to exit the Selman Bat Cave. There are still bats leaving the cave after dark when bat watchers can no longer see them.
On the night I was there, a couple of red-tailed hawks and a great-horned owl showed up hoping to intercept a bat for an easy meal.
The Wildlife Department bought the land where the Selman Bat Cave is in 1995 to protect and preserve it. The other three caves in the state that Mexican free-tail bats use as maternity caves are on private land.
A year after buying the land for the Selman Wildlife Management Area, the Wildlife Department began offering "bat watches" to the public. Each spring, those interested in making the trek to the cave must apply and hope to be one of the 75 people selected for a Friday or Saturday night "bat watch" in July.
The public bat watches are limited to 75 viewers per night to minimize the noise and not disturb the bats, Hickman said. Most of the spectators come from Oklahoma, Texas and Kansas, but over the years bat watchers have traveled from countries as far away as Japan, Belgium and the Netherlands, she said.
By the end of August, the bats begin their migration back to Mexico. But they will return to the Selman Bat Cave next summer, putting on another aerial show in the Oklahoma sky.
Hickman has been watching the bat show for 24 years and says it is a different experience each time. Even after 24 years, she has trouble coming up with the right words to portray it.
"I have not been able to find a way to describe it," she said. "You just have to see it to just be in awe of it."
To watch a video on the Selman Bat Cave, visit NewsOk.com.