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During her regular walk to the research facility, scientist the researcher stoops near a small pond covered by thick plants and retrieves a compact green audio device.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive threat with consequences that scientists are starting to understand.

Although teeming with remarkable animals – such as centuries-old large turtles, marine lizards, and the famous birds that inspired Darwin's theory of evolution – the island chain near the coast of South America had long remained free of amphibians.

During the 1990s, this shifted. Some small tree frogs traveled from continental Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA studies indicate that, over the years, there have been multiple accidental arrivals to the archipelago, and the amphibians now have a firm presence on several locations: multiple locations.

The population is expanding so quickly that researchers have been struggling to monitor, calculating populations in the millions on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

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

They calculated 6,000 frogs in a solitary pond. "The calculations are still very low," says San José. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the acoustic disruption they cause. "The number of frogs and the noise – it's really incredible," says San José.

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

But local farmers say the calls are so raucous they prevent sleep at night.

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

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

Environmental Consequences Remains Unclear

The noise isn't the primary problem, however. While the amphibians has been in the islands for almost three decades, scientists still know very little about its impact on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very typical for invasive species to thrive, as they have none of their natural predators. The islands has 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A 2020 study indicates the invasive amphibians are voracious bug eaters, and might be disproportionately eating rare insects found exclusively on the islands, or reducing the nutrition of the islands' uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have shown some atypical traits, including living in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also highly variable, with some larvae becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a larva in her lab for six months.

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

Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and gradually increasing the salinity of lagoons in vain.

Research indicates applying caffeine – which is extremely poisonous to amphibians – or using electrocution could assist, but these methods aren't always secure for other rare island organisms.

Without answers to more of the fundamental issues about their biology and effect, removing the amphibians 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 DNA analysis will help her group make sense of the invasive species, financial support for the research has been hard to come by.

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