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On her daily walk to the research facility, biologist Miriam San José stoops near a small pond covered by dense vegetation and collects a small plastic sound recorder.

She had placed there through the night to capture the characteristic calls of the Fowler's snouted treefrog, known by local researchers as an non-native species with consequences that scientists are just beginning to understand.

Although teeming with remarkable wildlife – including ancient giant tortoises, marine iguanas, and the famous birds that sparked Darwin's theory of evolution – the island chain near the shoreline of South America had historically been free of frogs and toads.

During the 1990s, this shifted. Some small amphibians traveled from mainland the mainland to the archipelago, probably as stowaways on transport vessels.

DNA research 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: Isabela and Santa Cruz.

The numbers is growing so quickly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the protected Galápagos national park.

When San José tagged amphibians and attempted to find them in the subsequent week and a half, she could find just one tagged frog from time to time, suggesting their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

The amphibians' proliferation is clear from the acoustic chaos they create. "The amount of frogs and the noise – it's really incredible," comments San José.

For the researchers, their nightly mating calls are helpful in estimating their presence in remote areas, using recorders like the one near the workplace.

But nearby agricultural workers say the sounds are so raucous they prevent sleep at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Remains Unclear

The noise isn't the primary problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its effect on the archipelago's precariously balanced land and water environments.

On islands, it is very typical for invasive species to thrive, as they have none of their enemies. The islands has over sixteen hundred introduced species, many of which are significantly disrupting the survival of its native ones.

A 2020 research indicates the invasive frogs are hungry bug eaters, and might be disproportionately eating rare bugs found exclusively on the archipelago, or depleting the food sources of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also highly variable, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which remained as a larva in her lab for half a year.

"We truly don't know this aspect," she says, worried the tadpoles could be impacting the islands' freshwater, a very limited commodity in Galápagos.

Techniques to curb the amphibians in the beginning of the century were largely ineffective. Conservation officers tried collecting significant quantities by hand and gradually raising the salinity of ponds in vain.

Studies suggests spraying coffee – which is highly poisonous to amphibians – or using electrical methods could assist, but these approaches aren't always secure for other rare Galápagos species.

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

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and genetic analysis will help her team understand of the invader, funding for the project has been hard to obtain.

"Everyone wants to give support for protecting frogs," says the researcher. "But it's harder to find funding for an introduced frog that you might want to control."