Forget the nightmares. Houston’s bats are winged friends who like to show off at sunset.
Let’s face it right off the bat: some animals in nature get bad press. Despite being cast as the villains in mythology and fiction, bats are just doing what nature designed them to do, and that makes us all itch less at night.
In particular, we’re talking about the Mexican free-tailed bat, a furry, hand-sized night-flier that roost by the hundreds of thousands in trees, caves, and human-made structures like the Waugh Drive Bridge in Houston and the Congress Avenue Bridge in Austin.
Indeed, some of our lexicon around bats is a bat off the mark. For example, bats have excellent eyesight according to the Houston Audubon Society, so that takes care of “blind as a bat.” Yet, bats do use sound to echolocate what’s around them (like dolphins) by bouncing sound off objects. It also helps them maneuver without a massive pileup when they exit their roosts.
“At sunset, the bats fly out all together toward the east,” explained Diana Foss, wildlife biologist and local guide with the Texas Parks and Wildlife Department in Houston. “They fly out in a cloud and then split up.”
There are an estimated 300,000-plus free-tailed bats living under the Waugh Drive Bridge. When they fly out they start work immediately, eating all kinds of insects, Foss said, including beetles, grasshoppers, and fortunately for us, mosquitoes. “After midnight, most of their diet consists of moths.” Collectively full of thousands of pounds of bugs, the bats return to their roost shortly before sunrise.
The bats started setting up house under the bridge in 1993. As their numbers and presence became more obvious and more popular with viewers, an observation deck was added in 2004. There are other bat-viewing options, including a bike path and a hiking trail. There’s also the Spirit of the Bayou pontoon boat.
The best bat-viewing vantage point?
“Any place there is great. On the ground, you can watch the bats come out above you. Really cool. You can stand on top of the bridge and watch bats come out from under your feet,” Foss offered.
“They are so beneficial to our ecosystem and yet people are so worried about having bats around.”
The “bat emergence,” as it’s called, takes place nightly and can attract a couple of hundred people, depending on the weather, Foss said. “Die-hards even come out in the rain,” as do the bats, of course.
One of Foss’ duties is to attend the bat emergence,provide some insight into bats, and to chat with visitors. “When I’m down there talking about bats, there are some people who arrive who are squeamish and are a little standoffish. The rest are pro-bats.”
Foss shares bat facts with the crowd as the emergence begins, and she says the combination usually turns everyone into bat fans. After we spoke, it was clear why she’s an ideal person to lead a team of experts that can comfort a crowd.
“I’ve loved bats,” she said candidly, “for 30 years.”
When the City of Houston proposed developing an interactive bat emergence experience, Foss volunteered to help research the concept and develop the personnel. Now she leads the Houston Bat Team.
“We wanted to make sure anything [the team] did wouldn’t affect or harm the bats’ behavior,” she said.
How did Foss become such a bat fan?
“They are so misunderstood is what attracted me to bats,” she said. “They are so beneficial to our ecosystem and yet people are so worried about having bats around.”
In fact, the Mexican free-tailed bat has been the official flying mammal of Texas since 1993. They’re one species of nearly a dozen living in the large caves and trees of the state’s Hill Country. Increasingly, they are also taking up residence in human-made structures and in urban environments.
The Waugh Drive Bridge colony is “probably the largest we know of out of 40 or so in Houston, all under bridges,” Foss said.
Standing with bat-watchers at the Waugh Drive Bridge as the bats emerge, Foss and her volunteers get lots of questions.
“The most common question: What do they eat? They’re happy to know they don’t eat blood. They ask why [the bats] do something. ‘Why do they do a swirl like a mini-tornado when they come out of the bridge?’ They’re probably gathering information—listening for predators [or] which direction the wind is coming from,” Foss explained.
“They’re flying into the wind, getting lift to get higher and to avoid flying predators.”
Like the tourists and the other locals, predators show up for the bat emergence each night too.
“We have black-crowned night herons, hawks, peregrine falcons and even great horned owls. They prey on bats when they come out,” she said. “We have seen a behavior change when lots of predators are around. The bats may wait a little longer in order to come out in darkness so the hawks can’t see them very well.”
Viewers also often ask about the other big, bad bat myth—rabies. As Glenn Olsen notes on the Houston Audubon website, “Bats are not a major source of rabies. Dogs, cats, raccoons, and skunks are much more likely to have the disease.”
“A lot of people don’t know they’re not scary. They’re keeping us from being drowned in mosquitoes.”
During the summer and early fall, the Mexican free-tailed bats hang around under the bridge, coming out every night to feed. “They are seasonal,” Foss explained. “From April all the way to November, the bats come out every night. If it’s raining, the bats wait for the rain to go away. The rain drops interfere with their echolocation.”
If it’s raining really hard, the bats just stay in. They can be seen in the daytime hanging from the bridge structure. But it’s look and don’t annoy. Bats are a protected species under Texas law, Foss pointed out.
As winter approaches, two-thirds of the colony go south.
“We don’t know exactly where this colony goes. Probably to a cave system in Mexico. They could go all the way to South America,” Foss said.
The remaining bats stay dormant (although when there are warm nights, they might come out for a midnight snack.) Fortunately, the free-tailed bat is a hearty species.
“Climate change doesn’t seem to affect them at all,” Foss said.
She explained that they seem to be resistant to white-nose syndrome, a disease that’s devastated other bat populations in the United States. “The fungus doesn’t seem to affect them. Other species, it can kill them.”
There are huge populations of Mexican free-tailed bats throughout the state. Bracken Cave near San Antonio is home to about 20 million bats. In Austin, the prime view is the Congress Avenue Bridge. Here, the bat emergence is bigger—perhaps as many as 1.5 million—and louder.
“The flapping of wings sounds like millions of pages being turned all at once. They also make a high-pitched chirping, chattering sound,” offered Duncan Hicks, development and grants coordinator for Merlin Tuttle’s Bat Conservation. “You can hear it before they emerge if you stand close enough to the bridge.
“Even more impressive is the sound they make while returning. While diving, they can cut through the air so fast that it whistles.”
For Hicks, an Austin native, “It’s one of the best sights you can see while being in a big city. It makes you feel like you’re connected to nature. A lot of people don’t know they’re not scary. They’re keeping us from being drowned in mosquitoes.”
