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During her daily commute to the research facility, biologist the researcher stoops near a shallow pond covered by dense plants and collects a small plastic sound recorder.

She had placed there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native species with consequences that experts are starting to comprehend.

Although teeming with remarkable wildlife – including ancient large turtles, marine iguanas, and the famous birds that inspired Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained free of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs traveled from mainland Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a strong foothold on two islands: Isabela and Santa Cruz.

The population is growing so quickly that scientists have been struggling to monitor, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the subsequent week and a half, she could locate only a single marked frog occasionally, indicating their populations were enormous.

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

The frogs' proliferation is evident from the sound disruption they cause. "The amount of frogs and the noise – it's truly incredible," comments the scientist.

For the researchers, their nocturnal vocalizations are helpful in estimating their presence in far-flung areas, using audio devices like the one outside the workplace.

But local agricultural workers say the sounds are so raucous they keep them up at night.

"In the rainy period, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.

"Initially it was a shock, observing the first frogs in the area," says Larrea Saltos, who started observing their abundance about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the Galápagos for nearly three decades, scientists still know very little about its effect on the islands' delicately balanced land and water environments.

On islands, it is very common for invasive species to thrive, as they have few of their natural predators. The islands counts 1,645 invasive types, many of which are significantly affecting the survival of its native ones.

A 2020 study indicates the invasive frogs are hungry insect eaters, and might be unevenly consuming rare bugs found only on the archipelago, or reducing the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have shown some atypical characteristics, including surviving in slightly salty water, which is rare for frogs.

Their metamorphosis stage is also extremely inconsistent, with some larvae becoming frogs very rapidly and others taking a long time: San José observed one which stayed as a larva in her laboratory for half a year.

"We truly don't know this aspect," she says, worried the larvae could be impacting the region's freshwater, a very scarce resource in the islands.

Techniques to control the frogs in the early 2000s were mostly ineffective. Conservation officers tried collecting significant quantities by hand and gradually raising the salt content of lagoons in vain.

Research indicates applying coffee – which is highly toxic to frogs – or using electrical methods could help, but these approaches aren't always secure for other rare island species.

Lacking solutions to more of the basic questions about their lifestyle and effect, culling the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and genetic examination will assist her team understand of the invader, funding for the research has been hard to come by.

"Everybody wants to give funding for protecting frogs," says San José. "But it's more difficult to find funding for an introduced frog that you might want to manage."