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During her daily walk to the research facility, scientist the researcher crouches near a shallow pond covered by dense vegetation and retrieves a small green sound recorder.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native species with effects that scientists are starting to comprehend.

Although abounding with remarkable animals – including ancient giant tortoises, marine iguanas, and the famous birds that inspired Charles Darwin's theory of evolution – the island chain off the coast of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this changed. Several small amphibians traveled from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.

Genetic research indicate that, over the years, there have been repeated accidental arrivals to the islands, and the frogs now have a firm presence on two locations: Isabela and Santa Cruz.

The population is expanding so rapidly that scientists have been finding it difficult to keep track, estimating populations in the millions on each island, across developed and farming areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the following week and a half, she could find just one marked frog from time to time, suggesting their numbers were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says the researcher. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nightly mating calls are helpful in determining their presence in remote areas, using recorders like the one near the office.

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

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

"At first it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her hand as she was stepping out of her front door.

Environmental Consequences Remains Unclear

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly 30 years, experts still know limited information about its effect on the islands' delicately balanced land and water ecosystems.

On archipelagos, it is very typical for non-native species to thrive, as they have few of their natural predators. The Galápagos has over sixteen hundred invasive species, many of which are seriously disrupting the safety of its native ones.

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

Unique Characteristics and Control Challenges

The Galápagos amphibians have shown some atypical traits, including living in slightly salty water, which is uncommon for frogs.

Their metamorphosis process is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: the researcher observed one which stayed as a larva in her lab for six months.

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

Techniques to control the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by hand and slowly raising the salinity of lagoons in without success.

Research indicates spraying coffee – which is highly poisonous to amphibians – or using electrocution could help, but these methods aren't always secure for other rare island species.

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

Funding Challenges for Research

While she expects the growing use of eDNA methods and DNA analysis will help her group understand of the invasive species, financial support for the research has been difficult to come by.

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