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During her regular walk to the research facility, biologist the researcher crouches near a small water body covered by thick plants and retrieves a compact plastic audio device.

The device was left there overnight to capture the characteristic calls of the Scinax quinquefasciatus, known by local researchers as an invasive species with effects that scientists are starting to understand.

Although abounding with remarkable wildlife – including centuries-old giant tortoises, swimming lizards, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had long remained devoid of amphibians.

In the late 1990s, this changed. Several small amphibians made their way from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.

DNA studies indicate that, over the years, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm foothold on several locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that researchers have been finding it difficult to monitor, estimating numbers in the millions on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent 10 days, she could find only a single tagged frog occasionally, indicating their numbers were massive.

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

Acoustic Chaos and Rising Worries

The amphibians' proliferation is clear from the sound disruption they cause. "The number of frogs and the noise – it's really incredible," says the scientist.

For the scientists, their nightly mating calls are helpful in estimating their presence in far-flung areas, using recorders like the one outside the workplace.

But nearby farmers say the calls are so raucous they keep them up at night.

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

"At first it was a shock, seeing the initial frogs in the region," says the farmer, who started observing their abundance about several years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly three decades, scientists still know very little about its impact on the islands' precariously balanced land and water environments.

On archipelagos, it is very typical for invasive species to thrive, as they have none of their enemies. The islands counts over sixteen hundred invasive types, many of which are significantly affecting the safety of its endemic ones.

A recent study suggests the invasive amphibians are hungry bug eaters, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or reducing the nutrition of the region's uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

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

Their development stage is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her lab for half a year.

"We really don't know this part," she says, concerned the larvae could be affecting the region's freshwater, a very scarce commodity in the islands.

Techniques to curb the frogs in the beginning of the century were mostly ineffective. Park rangers tried collecting significant quantities by hand and slowly increasing the salt content of lagoons in without success.

Studies suggests applying caffeine – which is highly toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other uncommon island species.

Without answers to more of the fundamental issues about their biology and impact, removing the frogs might not even be the right way to proceed, says San José.

Funding Challenges for Research

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

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