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During her daily walk to the research facility, scientist the researcher crouches near a shallow pond surrounded by thick vegetation and collects a small green sound recorder.

She had placed there overnight to record the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive species with effects that experts are just beginning to comprehend.

Although abounding with remarkable animals – including ancient large turtles, marine lizards, and the well-known finches that sparked Darwin's theory of evolution – the island chain near the coast of South America had historically been free of amphibians.

In the late 1990s, this shifted. Several tiny tree frogs made their way from continental Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA research suggest that, through time, there have been multiple accidental introductions to the archipelago, and the amphibians now have a firm foothold on several islands: Isabela and Santa Cruz.

The population is expanding so quickly that scientists have been finding it difficult to monitor, calculating populations in the millions on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José tagged frogs and attempted to recapture them in the subsequent 10 days, she could find only a single tagged frog from time to time, indicating their numbers were enormous.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nightly mating calls are useful in estimating their existence in remote areas, using recorders like the one near San José's workplace.

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

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

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

Ecological Impact Stays Unclear

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

On islands, it is very common for non-native organisms to thrive, as they have none of their enemies. The islands has 1,645 invasive types, many of which are significantly disrupting the survival of its endemic ones.

A recent study suggests the non-native amphibians are hungry bug eaters, and might be disproportionately eating uncommon insects found only on the islands, or depleting the nutrition of the region's rare avian species, disrupting the food chain.

Unusual Traits and Control Challenges

The Galápagos frogs have shown some atypical characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also highly variable, with some tadpoles becoming frogs very quickly and others taking a extended period: San José witnessed one which remained as a tadpole in her lab for six months.

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

Methods to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried capturing significant quantities by manual methods and gradually raising the salinity of lagoons in without success.

Research indicates applying coffee – which is extremely toxic to frogs – or using electrocution could assist, but these methods aren't always secure for other uncommon island organisms.

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

Financial Obstacles for Study

While she expects 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 hard to obtain.

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