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During her daily commute to the research facility, scientist the researcher stoops near a shallow water body surrounded by thick vegetation and retrieves a compact green audio device.

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

Despite abounding with remarkable wildlife – such as centuries-old giant tortoises, swimming lizards, and the famous birds that inspired Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had historically been free of amphibians.

During the 1990s, this shifted. Some small tree frogs made their way from mainland Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic studies suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a firm presence on two islands: multiple locations.

The population is growing so quickly 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 protected Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the subsequent week and a half, she could find only a single tagged frog from time to time, indicating their numbers were massive.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says San José. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the sound chaos they cause. "The number of frogs and the noise – it's really insane," says San José.

For the scientists, their nocturnal vocalizations are useful in determining their presence in far-flung areas, using recorders like the one outside the workplace.

But nearby agricultural workers 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 Jadira Larrea Saltos from Santa Cruz.

"Initially 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 house.

Environmental Consequences Remains Unknown

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly 30 years, scientists still know limited information about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive organisms to thrive, as they have none of their natural predators. The Galápagos has 1,645 introduced types, many of which are seriously disrupting the safety of its native ones.

A 2020 research indicates the invasive frogs are voracious insect eaters, and might be unevenly consuming rare bugs found only on the archipelago, or depleting the food sources of the islands' rare birds, affecting the food chain.

Unique Characteristics and Management Difficulties

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

Their development stage is also highly variable, with some larvae turning into frogs very quickly and others taking a extended period: the researcher witnessed one which stayed as a larva in her lab for half a year.

"We really don't know this aspect," she says, concerned the larvae could be affecting the islands' freshwater, a very limited resource in the islands.

Methods to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried collecting large numbers by manual methods and slowly raising the salt content of lagoons in without success.

Studies suggests applying caffeine – which is extremely poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily safe for other uncommon island species.

Without solutions to more of the basic issues about their lifestyle and impact, removing the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she expects the increasing use of environmental DNA methods and DNA analysis will help her team understand of the invader, funding for the research has been difficult to obtain.

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