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During her regular walk to the scientific station, biologist the researcher crouches near a small water body surrounded by dense vegetation and collects a compact plastic sound device.

She had placed there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with consequences that scientists are starting to comprehend.

Despite teeming with unique animals – including ancient large turtles, swimming iguanas, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had historically been free of amphibians.

In the late 1990s, this changed. Some tiny tree frogs traveled from continental the mainland to the archipelago, probably as stowaways on transport vessels.

Genetic research suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong presence on two islands: multiple locations.

The population is growing so rapidly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on every island, across urban and agricultural areas, but also in the protected Galápagos national park.

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

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," says San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the sound – it's really incredible," comments San José.

For the researchers, 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 prevent sleep at night.

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

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

Environmental Consequences Stays Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost three decades, experts still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for non-native organisms to prosper, as they have none of their natural predators. The Galápagos has 1,645 invasive types, many of which are seriously affecting the safety of its endemic ones.

A recent study suggests the non-native frogs are hungry bug consumers, and might be unevenly consuming uncommon bugs found only on the islands, or reducing the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The island amphibians have shown some unusual characteristics, including living in brackish water, which is rare for amphibians.

Their metamorphosis stage is also extremely variable, with some tadpoles becoming 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 truly don't know this part," she says, concerned the larvae could be impacting the region's freshwater, a very limited resource in Galápagos.

Methods to control the amphibians in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by hand and slowly raising the salinity of lagoons in vain.

Research suggests spraying coffee – which is extremely poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily safe for other uncommon Galápagos organisms.

Without solutions to more of the basic questions about their lifestyle and effect, culling the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she hopes the growing use of eDNA methods and genetic examination will help her group understand of the invasive species, financial support for the project has been hard to come by.

"Everyone wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to manage."