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On her regular walk to the research facility, biologist the researcher stoops near a shallow water body surrounded by thick plants and retrieves a compact green sound recorder.

She had placed there through the night to capture the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native threat with effects that experts are starting to comprehend.

Despite abounding with remarkable wildlife – such as centuries-old large turtles, swimming lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this changed. Several tiny amphibians made their way from continental Ecuador to the archipelago, likely as stowaways on cargo ships.

DNA studies suggest that, over the years, there have been repeated accidental arrivals to the archipelago, and the amphibians now have a firm foothold on two islands: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been struggling to monitor, estimating numbers in the millions on each island, across developed and agricultural areas, but also in the protected Galápagos national park.

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

They estimated six thousand frogs in a single pond. "The calculations are still very low," says San José. "I'm quite certain there are even more."

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the acoustic disruption they create. "The number of frogs and the noise – it's really insane," says the scientist.

For the scientists, their nocturnal vocalizations are useful in determining their existence in remote areas, using recorders like the one outside San José's workplace.

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

"In the rainy period, I constantly hear their calls and they're really loud," says a local coffee farmer from the island.

"At first it was a surprise, seeing the initial frogs in the area," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

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

On islands, it is very typical for non-native organisms to thrive, as they have few of their enemies. The Galápagos has 1,645 invasive species, many of which are seriously disrupting the survival of its endemic ones.

A 2020 research suggests the non-native amphibians are voracious bug consumers, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or reducing the food sources of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

The Galápagos frogs have exhibited some atypical characteristics, including surviving in slightly salty water, which is rare for amphibians.

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

"We really don't know this aspect," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited commodity in Galápagos.

Techniques to curb the amphibians in the beginning of the century were mostly ineffective. Park rangers tried capturing significant quantities by manual methods and slowly raising the salt content of lagoons in vain.

Research suggests spraying caffeine – which is highly poisonous to frogs – or using electrical methods could help, but these methods aren't always safe for other rare Galápagos organisms.

Without answers to more of the fundamental questions about their lifestyle and impact, culling the amphibians might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she expects the growing use of environmental DNA methods and DNA examination will help her group understand of the invader, financial support for the research 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 manage."