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During her regular commute to the research facility, scientist Miriam San José crouches near a shallow water body covered by thick vegetation and collects a compact plastic sound recorder.

She had placed there overnight to record the characteristic croaks of the Fowler's snouted treefrog, known by Galápagos researchers as an non-native threat with effects that experts are starting to comprehend.

Despite teeming with remarkable wildlife – such as ancient large turtles, swimming lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago off the coast of Ecuador had long remained free of frogs and toads.

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

Genetic studies suggest that, through time, there have been repeated accidental introductions to the islands, and the frogs now have a firm presence on several locations: multiple locations.

The numbers is expanding so rapidly that researchers have been struggling to monitor, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the following 10 days, she could find just one tagged frog occasionally, indicating their populations were massive.

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

Deafening Noise and Growing Concerns

The amphibians' abundance is evident from the sound chaos they cause. "The number of frogs and the sound – it's really insane," comments the scientist.

For the scientists, their nocturnal mating calls are useful in determining their existence in remote areas, using audio devices like the one outside the office.

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

"In the rainy period, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

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

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, however. While the species has been in the islands for almost three decades, experts still know limited information about its impact on the islands' 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 Galápagos has 1,645 invasive types, many of which are significantly affecting the survival of its native ones.

A recent study indicates the non-native frogs are hungry bug consumers, and might be disproportionately consuming rare bugs found exclusively on the archipelago, or reducing the food sources of the islands' uncommon avian species, disrupting the food chain.

Unusual Traits and Management Difficulties

The island frogs have shown some unusual characteristics, including living in slightly salty water, which is rare for frogs.

Their development process is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José witnessed one which remained as a tadpole in her laboratory for six months.

"We really don't know this part," she says, concerned the tadpoles could be impacting the islands' clean water, a very limited commodity in the islands.

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

Research indicates spraying caffeine – which is highly toxic to amphibians – or using electrocution could assist, but these methods aren't always secure for other uncommon Galápagos species.

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

Financial Obstacles for Research

While she expects the increasing use of eDNA techniques and genetic examination will help her team make sense of the invasive species, financial support for the project has been difficult to come by.

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