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

The device was left there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by local researchers as an non-native species with consequences that experts are just beginning to comprehend.

Despite teeming with unique wildlife – including centuries-old large turtles, swimming lizards, and the famous finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had historically been free of amphibians.

During the 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as stowaways on transport vessels.

Genetic studies suggest that, over the years, there have been multiple accidental arrivals to the islands, and the frogs now have a firm foothold on two islands: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been finding it difficult to keep track, estimating numbers in the millions on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the following 10 days, she could locate just one tagged frog occasionally, suggesting their populations were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says San José. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nocturnal mating calls are useful in estimating their presence in remote areas, using audio devices like the one outside the office.

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

"During the rainy period, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, observing 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.

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, scientists still know limited information about its impact on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive species to prosper, as they have none of their natural predators. The islands counts over sixteen hundred introduced types, many of which are significantly disrupting the survival of its native ones.

A recent study indicates the invasive frogs are hungry bug eaters, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or depleting the food sources of the islands' uncommon avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos amphibians have exhibited some unusual characteristics, including surviving in brackish water, which is rare for amphibians.

Their development process is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher observed one which remained as a larva in her lab for six months.

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

Methods to control the amphibians in the early 2000s were largely unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly increasing the salt content of lagoons in without success.

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

Lacking answers to more of the basic issues about their lifestyle and effect, culling the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Study

While she expects the increasing use of eDNA methods and genetic analysis will help her team understand of the invasive species, funding for the project has been difficult to obtain.

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