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On her daily walk to the research facility, scientist the researcher crouches near a small pond covered by thick vegetation and collects a compact green sound recorder.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, known by local researchers as an non-native species with effects that experts are starting to understand.

Despite teeming with remarkable animals – such as centuries-old large turtles, marine iguanas, and the famous birds that sparked Charles Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained devoid of amphibians.

During the 1990s, this changed. Several tiny amphibians made their way from continental the mainland to the islands, probably as stowaways on transport vessels.

DNA studies indicate that, through time, there have been repeated accidental arrivals to the islands, and the amphibians now have a strong foothold on two locations: multiple locations.

The numbers is expanding so quickly that researchers have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the conservation natural reserve.

When San José tagged amphibians and attempted to recapture them in the following week and a half, she could find only a single tagged frog occasionally, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states the researcher. "I am pretty sure there are even more."

Deafening Noise and Growing Concerns

The amphibians' proliferation is clear from the sound chaos they cause. "The amount of frogs and the noise – it's really incredible," comments the scientist.

For the researchers, their nocturnal vocalizations are helpful in estimating their presence in far-flung areas, using recorders like the one outside the office.

But nearby farmers say the sounds are so raucous they keep them up at night.

"In the wet season, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.

"At first it was a shock, seeing the initial frogs in the region," says the farmer, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the primary problem, however. While the species has been in the islands for almost 30 years, scientists still know limited information about its impact on the islands' precariously balanced land and water environments.

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

A 2020 study suggests the invasive amphibians are voracious insect eaters, and might be unevenly consuming rare bugs found only on the archipelago, or reducing the nutrition of the region's uncommon birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also highly inconsistent, with some larvae becoming frogs very rapidly and others taking a long time: San José witnessed one which remained as a larva in her lab for half a year.

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

Techniques to curb the amphibians in the beginning of the century were largely ineffective. Park rangers tried collecting large numbers by manual methods and gradually increasing the salinity of lagoons in vain.

Research indicates applying caffeine – which is highly toxic to amphibians – or using electrical methods could help, but these methods aren't necessarily safe for other rare island species.

Without answers to more of the basic questions about their lifestyle and effect, culling the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Study

While she expects the growing use of eDNA methods and DNA examination will assist her team understand of the invader, financial support for the research has been difficult to come by.

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