This past weekend the kids, Jeff and I drove to Austin, Texas to visit our state’s capitol, and to take a boat ride to watch the Mexican free-tailed bats (Tadarida brasiliensis) emerge from beneath the Congress Avenue Bridge at dusk.
Until told by the boat tour guide, I had no idea the Congress Avenue Bridge was home to the world’s largest urban bat colony.
Apparently, the bats lived under the bridge for years, but when it was renovated in 1980, they began moving in by the thousands.
The engineers unintentionally created the ideal bat roost when they built a series of long, thin joints (measuring 1 inch wide and 17 inches deep) on the underside of the bridge. This offered protection against local predators like the red-tailed hawk. Our tour guide called the bridge the bats’ “concrete fortress of power”.
Though we could not actually see any of the bats wedged up in the crevices, when we passed under the bridge we could certainly SMELL them!
In the spring and summer months, there are an estimated 750,000 to 1.5 million bats at the peak of the bat-watching season.
They easily consume from 10,000 to 30,000 pounds of insects, including agricultural pests, on their nightly flights, and it is estimated they can eat up to 1200 mosquitoes in an hour.
Although we chose to take a bat watching cruise, many locals and tourists line up along the sidewalks on the bridge to view the bats’ nightly flights.
The bats emerge from under the bridge around sunset.
We boarded the boat at 7:00 PM, leaving the dock around 7:30 PM. Our tour guide explained that the bats normally flew between 8:00 and 8:30, but recently were flying earlier.
Thankfully, we were in a covered boat. While I realize the Mexican free-tail droppings (guano) make for wonderful fertilizer, I did not want to experience it on my person.
Remember the rumor that bat guano is used in the manufacture of mascara? I am so thankful that is not true. Interestingly enough, guano was once used to make gunpowder.
Most of this bat colony is female. They give birth to a single baby bat (a pup) in early June which explains the enormous population growth from early summer to spring.
At birth, pups barely weigh a tenth of an ounce, one-third as much as their mothers, which is the equivalent of a human giving birth to a 40-pound child. Pups learn to fly and join the other bats in hunting insects at about five weeks old.
Until then, mothers nurse the pups, eating nearly their full weight in insects each night.
When they return from a hunt, mother bats identify their young among thousands of other bats by their specific smell and sound.
The Mexican free-tailed bats can cover 50 miles or more one-way each night to hunt for moths and other insects.
Though not blind, the bats use echolocation, a sort of biological sonar system where they emit inaudible high-pitched sounds (about 10-20 beeps per second) and listen to the echoes, to hunt their flying prey in the dark.
Mexican free-tailed bats are considered the jets of the bat world for their speed. With tailwinds, they can clock up to 60 miles per hour.
I probably snapped fifty shots as the bats wove in and out, merging and dividing while flying out-of-sight beyond the city skyline.
The cruise lasted a bit over an hour, and even as our boat made its way back to dock, the bats still exited beneath the bridge like a thin, black cloud.
Ours was a memorable experience, to be certain. If you find yourself anywhere near Austin, Texas, I suggest planning the bat flights into your visit.
Heather Sanders is a leading homeschooling journalist who inspires homeschooling families across the nation. Married to Jeff, Heather lives in the East Texas Piney Woods and homeschools her three children, Emelie, Meredith and Kenny.