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During her daily commute to the research facility, scientist the researcher stoops near a shallow water body covered by thick vegetation and retrieves a compact green audio recorder.

The device was left there through the night to record the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive threat with consequences that experts are starting to understand.

Despite teeming with remarkable animals – such as centuries-old large turtles, swimming iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had long remained devoid of frogs and toads.

In the late 1990s, this shifted. Some tiny tree frogs made their way from mainland Ecuador to the archipelago, probably as stowaways on transport vessels.

DNA studies suggest that, through time, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm presence on several locations: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to monitor, estimating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged frogs and attempted to find them in the subsequent 10 days, she could locate just one marked frog from time to time, suggesting their populations were enormous.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' abundance is evident from the acoustic disruption they create. "The amount of frogs and the noise – it's truly insane," comments San José.

For the scientists, their nightly mating calls are useful in determining their presence in remote areas, using audio devices like the one outside the workplace.

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

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

"At first it was a surprise, observing 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 stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for non-native organisms to thrive, as they have none of their enemies. The Galápagos has 1,645 introduced species, many of which are seriously affecting the survival of its endemic ones.

A 2020 research suggests the invasive amphibians are hungry bug eaters, and might be disproportionately consuming rare insects found only on the islands, or reducing the food sources of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The island amphibians have exhibited some unusual traits, including living in brackish water, which is uncommon for frogs.

Their development stage is also highly variable, with some tadpoles becoming frogs very quickly and others taking a extended period: the researcher 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 tadpoles could be affecting the region's clean water, a very scarce resource in the islands.

Techniques to control the frogs in the early 2000s were largely unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly increasing the salt content of ponds in vain.

Studies indicates applying caffeine – which is extremely poisonous to frogs – or using electrocution could help, but these approaches aren't always secure for other uncommon island species.

Without answers to more of the fundamental questions about their lifestyle and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Study

While she expects the growing use of environmental DNA methods and genetic examination will help her group make sense of the invasive species, financial support for the project has been hard to come by.

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