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During her regular walk to the research facility, scientist the researcher stoops near a shallow pond surrounded by thick plants and retrieves a small green sound device.

The device was left there through the night to capture the characteristic calls of the Fowler's snouted treefrog, known by local researchers as an non-native threat with consequences that experts are just beginning to understand.

Despite teeming with unique wildlife – including centuries-old large turtles, marine lizards, and the well-known finches that sparked Charles Darwin's evolutionary theory – the island chain off the coast of South America had long remained devoid of amphibians.

In the late 1990s, this shifted. Several small tree frogs traveled from mainland Ecuador to the islands, probably as stowaways on transport vessels.

DNA research suggest that, over the years, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a strong presence on two locations: Isabela and Santa Cruz.

The population is growing so quickly that scientists have been finding it difficult to keep track, calculating populations in the millions 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 marked frog occasionally, suggesting their populations were massive.

They calculated six thousand frogs in a single pond. "Our estimates are still very low," states San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the sound chaos they create. "The number of frogs and the sound – it's really insane," says the scientist.

For the researchers, their nightly mating calls are useful in estimating their existence in far-flung areas, using audio devices like the one near San José's office.

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

"In the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the islands for almost 30 years, experts still know limited information about its impact on the archipelago's delicately balanced land and water ecosystems.

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

A 2020 study indicates the non-native amphibians are hungry insect eaters, and might be disproportionately eating uncommon bugs found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also extremely variable, with some larvae becoming frogs very quickly and others taking a long time: San José 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 impacting the islands' freshwater, a very scarce resource in the islands.

Techniques to curb the amphibians in the early 2000s were largely unsuccessful. Park rangers tried capturing large numbers by hand and slowly raising the salt content of ponds in vain.

Research suggests applying coffee – which is highly toxic to amphibians – or using electrocution could help, but these methods aren't always safe for other rare Galápagos species.

Without solutions to more of the basic issues about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and genetic examination will assist her group understand of the invasive species, funding for the project has been difficult to come by.

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