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During her regular walk to the research facility, biologist the researcher crouches near a shallow water body surrounded by dense plants and retrieves a small green audio recorder.

She had placed there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos researchers as an non-native species with effects that scientists are starting to comprehend.

Although teeming with remarkable wildlife – including ancient large turtles, marine iguanas, and the famous finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had long remained free of amphibians.

In the late 1990s, this changed. Several small tree frogs made their way from continental the mainland to the archipelago, likely as stowaways on transport vessels.

Genetic studies suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the amphibians now have a strong foothold on several locations: multiple locations.

The numbers is expanding so quickly that scientists have been struggling to keep track, estimating numbers in the millions on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could locate only a single marked frog occasionally, indicating their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states San José. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is clear from the acoustic disruption they create. "The amount of frogs and the noise – it's really insane," says the scientist.

For the researchers, their nightly vocalizations are helpful in determining their existence in far-flung areas, using audio devices like the one outside San José's workplace.

But nearby agricultural workers say the calls are so loud they keep them up at night.

"In the wet season, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a surprise, seeing the initial frogs in the area," says the farmer, who started noticing their large numbers about several years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for almost 30 years, scientists still know limited information about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive organisms to prosper, as they have few of their natural predators. The islands counts over sixteen hundred invasive types, many of which are significantly disrupting the survival of its native ones.

A 2020 study suggests the invasive amphibians are voracious bug eaters, and might be unevenly consuming rare insects found only on the archipelago, or depleting the food sources of the islands' rare avian species, affecting the food chain.

Unique Characteristics and Control Challenges

The Galápagos amphibians have shown some atypical traits, including surviving in brackish water, which is uncommon for amphibians.

Their development process is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José witnessed one which stayed as a larva in her lab for half a year.

"We truly don't know this aspect," she says, worried the larvae could be impacting the islands' clean water, a very scarce commodity in Galápagos.

Techniques to control the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually raising the salinity of ponds in without success.

Research suggests applying caffeine – which is extremely poisonous to frogs – or using electrocution could help, but these methods aren't always safe for other rare island organisms.

Without answers to more of the fundamental questions about their biology and impact, removing the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Study

While she expects the growing use of eDNA techniques and genetic examination will help her team make sense of the invasive species, funding for the project has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's harder to find funding for an invasive frog that you might want to control."