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On her regular commute to the research facility, scientist the researcher stoops near a shallow water body surrounded by thick plants and retrieves a compact green audio recorder.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by local researchers as an invasive species with consequences that scientists are just beginning to comprehend.

Although abounding with unique wildlife – such as ancient large turtles, swimming iguanas, and the well-known birds that sparked Charles Darwin's evolutionary theory – the island chain off the coast of South America had historically been free of amphibians.

During the 1990s, this shifted. Several tiny amphibians traveled from continental the mainland to the archipelago, probably as hitchhikers on cargo ships.

DNA research suggest that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong presence on several locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on each island, across developed and agricultural areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to find them in the subsequent 10 days, she could locate only a single marked frog occasionally, suggesting their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm quite certain there are even more."

Deafening Noise and Growing Concerns

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

For the scientists, their nocturnal vocalizations are helpful in determining their existence in remote areas, using audio devices like the one near the workplace.

But nearby agricultural workers say the calls are so loud they prevent sleep at night.

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

"Initially it was a shock, observing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her palm as she was walking out of her front door.

Ecological Impact Stays Unclear

The noise isn't the primary problem, however. While the amphibians has been in the islands for almost 30 years, scientists still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very common for non-native organisms to prosper, as they have few of their enemies. The islands has 1,645 introduced species, many of which are seriously disrupting the safety of its native ones.

A 2020 study suggests the invasive amphibians are hungry bug consumers, and might be unevenly consuming rare bugs found exclusively on the archipelago, or reducing the food sources of the region's uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos frogs have exhibited some unusual characteristics, including living in slightly salty water, which is uncommon for frogs.

Their metamorphosis process is also highly variable, with some larvae becoming frogs very quickly and others taking a long time: San José witnessed one which remained as a tadpole in her laboratory for half a year.

"We really don't know this aspect," she says, worried the tadpoles could be impacting the islands' clean water, a very limited commodity in the islands.

Techniques to curb the frogs in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by manual methods and gradually raising the salt content of lagoons in without success.

Research suggests spraying caffeine – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't necessarily safe for other rare island species.

Lacking answers to more of the fundamental questions about their biology and effect, culling the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the increasing use of eDNA methods and DNA analysis will help her group make sense of the invasive species, financial support for the research has been hard to come by.

"Everyone wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an introduced frog that you might want to control."