Glass frogs ‘wave’ to communicate near noisy waterfalls

  • A researcher discovered that an obscure species of nocturnal glass frog, Sachatamia orejuela, uses visual signaling as well as acoustical calls to communicate within their environment.
  • Other frog species are known to communicate visually, although they are unrelated to S. orejuela and are found on different continents.
  • A recent paper on the discovery also provides the first known description of the acoustical call of S. orejuela, endemic to Ecuador and Colombia.

Becca Brunner was standing chest-deep in an Ecuadoran rainforest stream, holding up audio equipment as she recorded the high-pitched call of an elusive glass frog. But then she encountered something unexpected: the frog was fluttering its front and back legs as well as bobbing its head.

“I was basically in the pool of water that was right underneath the waterfall with my microphone,” Brunner, a doctoral candidate at the University of California, Berkeley, told Mongabay in an interview. “When I noticed that it was doing these flipping movements, I got even more excited, of course, but I had to come out of the stream.”

Brunner climbed the steep, slick waterfall, and balanced precariously on one foot to capture video of the frog’s waving routine. “You’d have to be a crazy person like me to scale a slippery waterfall to find this out,” she said.

But to Brunner, her efforts were worth it. She had discovered that the glass frog (Sachatamia orejuela), which mainly lives in the spray zones of waterfalls, didn’t just communicate acoustically, but also used visual signaling. While it’s still not clear why these frogs wave their limbs and bob their heads, Brunner says it’s likely to attract females or to lay claim to territory, although this needs further investigation.

“The really cool thing about the waving is that they need to add this other component because they live near really loud environments,” said Brunner, who co-authored a paper on the discovery. “That’s the most exciting part to me. They’ve adapted their behavior over time, like an evolutionary timescale to be able to communicate in this niche.”

S. orejuela, a nocturnal species with greenish, reflective skin, isn’t the only frog to communicate this way. Other frog species, including Brazil’s Hylodes japi, India’s Micrixalus saxicola, and Borneo’s Staurois latopalmatus, also display visual signals such as hand and foot waving, according to the paper. Yet none of these frogs live on the same continent, nor do they belong to the same family, which means that all of these behaviors evolved separately, Brunner said. In biological terms, this is called behavioral convergent evolution.

“The motions [of the different frog species] are a bit different, but the function is the same: they’re trying to add a visual component in addition to their calling so that they have a higher chance of being seen by females,” Brunner said.

The Sachatamia orejuela frog is found in the spray zones of waterfalls. Image by Becca Brunner.

“Another example of convergent evolution is flight,” she added. “So birds and bats both fly, but they’re not very related to each other [since] one’s a mammal and one’s a bird. But they still have evolved these separate ways to do it but for the same reasons.”

The paper also provides the first known description of the audial call of S. orejuela, Brunner said.

“It’s super high pitched,” she said. “It’s hard to hear, which is probably one of the reasons why it hasn’t been recorded before, beyond the fact that you have to get really wet to record it.”


Before the publication of this study, very little was known about this particular species of glass frog, which was first described in a study published in 1989. The species, which is found in forests and wetlands in Ecuador and Colombia, is classified as a species of “least concern” by the IUCN, although populations are believed to be decreasing mainly due to water pollution from chemicals used in illegal crops.

Study co-author Juan Guayasamin, a glass frog expert and professor at Universidad San Francisco in Quito, Ecuador, said he was thrilled when he first saw Brunner’s video.

“We (batrachologists) always wondered how frogs communicate in environments where noise is extremely loud, like cascades,” Guayasamin told Mongabay in an email. “It takes a very committed person to actually find out. Observing glassfrogs under those conditions (tons of water falling on your head) is almost impossible. Becca managed to observe them and, somehow, even record them.”

He said this discovery was somewhat surprising since “waving” behaviors are usually seen in diurnal species, not nocturnal ones like S. orejuela.

Researcher Becca Brunner scaling a waterfall to capture footage of the waving glass frog. Image by Becca Brunner.

“[We] always worked under the assumption that the [species] just had a very high-pitched call to communicate,” he said. “Sometimes it is really nice when you are wrong.”

He added: “I think that the main take-home message is that in-depth field work always turns out in finding the unexpected. In a time where most students spend their time in laboratories, we should make an effort to explore and understand nature.”

Citation:

Brunner, R. M., & Guayasamin, J. M. (2020). Nocturnal visual displays and call description of the cascade specialist glassfrog Sachatamia orejuela. Behaviour, 157(14-15), 1257-1268. doi:10.1163/1568539x-bja10048

Banner image caption: Sachatamia orejuela. Image by Becca Brunner.

Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.

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This story first appeared on Mongabay

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