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During her daily walk to the research facility, scientist Miriam San José crouches near a shallow pond surrounded by thick vegetation and collects a compact green sound device.

The device was left there through the night to capture the distinctive croaks of the Fowler's snouted treefrog, known by local scientists as an non-native species with consequences that scientists are just beginning to comprehend.

Although teeming with unique animals – including ancient giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's evolutionary theory – the Galápagos archipelago near the coast of Ecuador had historically been free of amphibians.

In the late 1990s, this changed. Some small amphibians traveled from mainland the mainland to the archipelago, likely as hitchhikers on cargo ships.

DNA studies indicate that, over the years, there have been repeated unintentional arrivals to the islands, and the amphibians now have a firm presence on two locations: multiple locations.

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

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

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are additional numbers."

Deafening Noise and Growing Concerns

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

For the researchers, their nocturnal mating calls are useful in determining their presence in far-flung areas, using recorders like the one outside the office.

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

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

"Initially it was a shock, seeing the initial frogs in the region," says the farmer, who started observing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Stays Unknown

The sound isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On islands, it is very common for non-native organisms to prosper, as they have few of their natural predators. The Galápagos has 1,645 introduced types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study suggests the non-native frogs are voracious bug consumers, and might be disproportionately consuming rare bugs found exclusively on the islands, or reducing the nutrition of the islands' rare birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: San José witnessed one which remained as a tadpole in her lab for half a year.

"We really don't know this aspect," she says, concerned the tadpoles could be affecting the islands' clean water, a very scarce resource in Galápagos.

Methods to curb the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried collecting significant quantities by hand and gradually increasing the salt content of lagoons in without success.

Studies indicates spraying coffee – which is extremely poisonous to frogs – or using electrical methods could help, but these methods aren't always secure for other uncommon island species.

Lacking answers to more of the basic issues about their biology and impact, culling the amphibians might not even be the right way to advance, says San José.

Financial Obstacles for Research

While she expects the growing use of eDNA techniques and genetic examination will assist her team make sense of the invader, financial support for the research has been hard to come by.

"Everyone wants to give funding for protecting frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to control."