Summer monsoons are the lifeline for West Texas, and when rains come the jubilation is general — as birds sing and bees buzz, grasses grow and ranchers rejoice.
In the West Texas mountains, a tiny creature adds its voice to the celebratory chorus. Chirping frogs are typically less than an inch long, and you could mistake their whistling, trilling calls for an insect’s. But these little creatures have an epic story, one that distills the deep mysteries of biodiversity.
Dr. Tom Devitt is a biologist at the University of Texas at Austin who studies chirping frogs, a group known scientifically as Syrrhophus.
“I just think they're really cool organisms,” Devitt said. “We can use them as a system to ask really interesting questions about ecology and evolution and behavior. It's a borderline obsession, I guess you could say.”
These frogs began their evolutionary journey in western Cuba. Somehow — perhaps on vegetation swept to sea in hurricanes — they crossed the Caribbean. Then, they flourished and diversified, from Mexico as far north as the Trans-Pecos and Texas Hill Country.
Arid country is an unlikely home for amphibians. But chirping frogs are “direct developers” — there are no tadpoles. Little frogs emerge from eggs, and parents, especially the males, care for the young, Devitt said.
And they’re a reclusive bunch, seeking “hidden retreats” in rocky crevices. That’s meant they’ve been little studied. Devitt is trying to understand their mysterious family tree.
“That's kind of where the focus of my work is,” Devitt said, “is at the species level, trying to figure out how many species there are. How do they differ from one another, and why are there so many species?”
That includes West Texas.
Chirping frogs were first identified here in the Chisos Basin in 1944. They were described as a new species, the spotted chirping frog. But in their appearance — of mottled yellow and brown — they’re virtually identical to the Hill Country’s cliff chirping frog. Some scientists argued they were a single species.
To resolve the question, Devitt is sequencing DNA. On summer nights, males call from their redoubts, announcing their presence to potential mates, and would-be competitors. Capturing them in the Chisos canyons isn’t easy.
‘It can be incredibly frustrating sometimes to locate an individual that's calling very sporadically and is very aware of your presence,” Devitt said, “and it doesn't want to be captured.”
In addition to genetics, Devitt is carefully comparing the size and coloration among frogs. He’s analyzing their courtship calls for subtle differences. His preliminary findings strongly suggest the Chisos frogs are a distinct species.
But across the science, it’s evident that the boundaries between species are not as clear-cut as biologists once thought. The frogs known in the Chisos are also found in the Davis Mountains and the Sierra Diablo and east toward Sanderson. The Hill Country frogs have been found near Fort Stockton. Devitt suspects the two species may be interbreeding and hybridizing along that frontier.
Tucked away among the rocks, awaiting a summer storm, a chirping frog’s existence might seem circumscribed. But these creatures live spirited lives. Devitt described a confrontation between two males, who’d staked claims to the same territory.
“They actually started wrestling each other,” he said. “And it was pretty mean. It was a very vigorous kind of grappling session. And at the end of it, you could see that there was a clear winner and a clear loser.”
A casual West Texas traveler is struck by the stark terrain, and suspects it to be lifeless. But as they call out in the night, chirping frogs remind us of the desert’s rich, hidden life.
