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On her regular walk to the research facility, biologist the researcher crouches near a small water body covered by dense plants and retrieves a small plastic audio device.

She had placed there through the night to capture the distinctive calls of the Scinax quinquefasciatus, known by local scientists as an non-native species with consequences that scientists are starting to comprehend.

Despite abounding with remarkable animals – including ancient giant tortoises, swimming iguanas, and the famous finches that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had long remained free of amphibians.

In the late 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the islands, likely as stowaways on cargo ships.

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

The numbers is growing so quickly that researchers have been struggling to keep track, calculating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could find only a single tagged frog occasionally, suggesting their populations were massive.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

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

For the researchers, their nocturnal mating calls are helpful in determining their existence in remote areas, using audio devices like the one near the workplace.

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

"During the rainy period, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a shock, seeing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about three years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Remains Unknown

The sound isn't the fundamental problem, though. While the species has been in the islands for almost 30 years, experts still know very little about its impact on the islands' delicately balanced land and water ecosystems.

On islands, it is very common for invasive species to thrive, as they have few of their enemies. The islands has over sixteen hundred introduced types, many of which are significantly disrupting the safety of its native ones.

A 2020 research indicates the non-native amphibians are hungry insect eaters, and might be unevenly consuming rare bugs found only on the islands, or reducing the food sources of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

The Galápagos amphibians have exhibited some atypical traits, including surviving in slightly salty water, which is rare for frogs.

Their development stage is also highly inconsistent, with some tadpoles turning into frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for six months.

"We really don't know this aspect," she says, concerned the larvae could be impacting the islands' freshwater, a very scarce commodity in Galápagos.

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

Research indicates applying caffeine – which is extremely toxic to frogs – or using electrocution could help, but these methods aren't necessarily safe for other uncommon island species.

Lacking solutions to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Study

While she expects the growing use of environmental DNA methods and DNA examination will help her team make sense of the invasive species, financial support for the research 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 manage."