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On her regular commute to the research facility, biologist Miriam San José crouches near a small water body covered by dense vegetation and retrieves a small green sound device.

The device was left there overnight to record the characteristic calls of the Scinax quinquefasciatus, known by local scientists as an non-native threat with consequences that scientists are starting to understand.

Despite teeming with unique wildlife – including ancient large turtles, swimming lizards, and the well-known birds that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had historically been devoid of amphibians.

In the late 1990s, this changed. Some small amphibians made their way from mainland Ecuador to the islands, likely as hitchhikers on transport vessels.

Genetic studies indicate that, over the years, there have been repeated accidental arrivals to the islands, and the amphibians now have a strong presence on several locations: multiple locations.

The population is growing so rapidly that researchers have been finding it difficult to keep track, estimating populations in the millions on each island, across developed and agricultural areas, but also in the protected Galápagos national park.

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

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

Acoustic Chaos and Rising Worries

The amphibians' proliferation is clear from the acoustic chaos they create. "The amount of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nocturnal mating calls are helpful in estimating their presence in far-flung areas, using audio devices like the one near the workplace.

But nearby agricultural workers say the calls are so loud they keep them up at night.

"During the rainy period, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, seeing the initial frogs in the area," says Larrea Saltos, who started noticing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The noise isn't the primary problem, though. 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 archipelagos, it is very common for non-native species to thrive, as they have few of their natural predators. The islands counts over sixteen hundred invasive types, many of which are seriously disrupting the safety of its native ones.

A 2020 research suggests the invasive amphibians are voracious insect consumers, and might be disproportionately consuming rare bugs found only on the islands, or depleting the nutrition of the region's rare avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

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

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

"We truly don't know this part," she says, concerned the larvae could be impacting the region's clean water, a very scarce commodity in the islands.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried collecting large numbers by manual methods and gradually increasing the salinity of ponds in without success.

Research indicates applying caffeine – which is extremely toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other rare Galápagos organisms.

Lacking answers to more of the fundamental issues about their biology and effect, removing the frogs might not even be the right way to advance, says San José.

Financial Obstacles for Study

While she expects the growing use of environmental DNA methods and DNA analysis will help her group make sense of the invasive species, financial support for the project has been hard to come by.

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