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During her daily walk to the research facility, scientist Miriam San José stoops near a small water body surrounded by thick vegetation and collects a compact plastic audio recorder.

She had placed there through the night to capture the characteristic calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native threat with effects that scientists are just beginning to understand.

Although teeming with remarkable wildlife – such as centuries-old giant tortoises, marine lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain off the shoreline of South America had long remained devoid of amphibians.

During the 1990s, this shifted. Several small amphibians traveled from mainland the mainland to the islands, probably as hitchhikers on cargo ships.

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

The population is expanding so rapidly that scientists have been struggling to monitor, calculating populations in the millions on every island, across urban and farming areas, but also in the conservation natural reserve.

When San José tagged amphibians and attempted to find them in the subsequent 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. "The calculations are still very conservative," states San José. "I'm quite certain there are even more."

Deafening Noise and Rising Worries

The amphibians' proliferation is evident from the acoustic disruption they create. "The number of frogs and the sound – it's really incredible," comments San José.

For the researchers, their nightly vocalizations are helpful in determining their existence in remote areas, using audio devices like the one near San José's office.

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

"In the wet season, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, seeing the initial frogs in the area," says the farmer, who started observing their abundance about three years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the primary problem, though. While the species has been in the islands for nearly 30 years, experts still know very little about its impact on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive species to thrive, as they have few of their natural predators. The Galápagos has 1,645 invasive types, many of which are significantly disrupting the safety of its native ones.

A 2020 study indicates the invasive amphibians are hungry bug eaters, and might be unevenly eating rare insects found exclusively on the archipelago, or depleting the nutrition of the region's rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also highly variable, with some larvae turning into frogs very rapidly and others taking a long time: the researcher witnessed one which stayed as a tadpole in her lab for half a year.

"We truly don't know this aspect," she says, worried the larvae could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to control the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and slowly raising the salinity of ponds in vain.

Studies suggests spraying caffeine – which is extremely poisonous to frogs – or using electrocution could assist, but these approaches aren't always secure for other rare island species.

Lacking answers to more of the fundamental questions about their biology and impact, culling the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of eDNA techniques and genetic examination will assist her team make sense of the invasive species, funding for the research has been difficult to come by.

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