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During her regular commute to the scientific station, biologist the researcher stoops near a shallow water body surrounded by thick vegetation and retrieves a compact plastic audio recorder.

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, known by Galápagos scientists as an invasive threat with effects that experts are just beginning to comprehend.

Although abounding with remarkable wildlife – including ancient large turtles, swimming lizards, and the well-known finches that sparked Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had historically been free of frogs and toads.

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

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

The population is expanding so rapidly that researchers have been finding it difficult to keep track, estimating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to find them in the subsequent week and a half, she could find only a single marked frog occasionally, suggesting their populations were massive.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," states the researcher. "I'm quite certain there are even more."

Deafening Noise and Growing Concerns

The frogs' abundance is evident from the sound disruption they cause. "The amount of frogs and the noise – it's truly insane," says the scientist.

For the scientists, their nightly vocalizations are helpful in determining their presence in far-flung areas, using audio devices like the one near San José's office.

But nearby farmers say the calls are so loud they prevent sleep at night.

"In the wet season, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unclear

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

On islands, it is very typical for invasive organisms to thrive, as they have few of their enemies. The islands counts 1,645 introduced species, many of which are significantly affecting the survival of its native ones.

A recent study suggests the non-native frogs are voracious bug eaters, and might be unevenly eating uncommon insects found exclusively on the islands, or depleting the food sources of the islands' uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their development process is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: 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 larvae could be affecting the islands' freshwater, a very scarce commodity in the islands.

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

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

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

Funding Challenges for Study

While she hopes the increasing use of eDNA methods and DNA examination will assist her team understand of the invasive species, funding for the research has been hard to obtain.

"Everyone wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."