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During her regular commute to the scientific station, biologist Miriam San José stoops near a small pond covered by thick vegetation and retrieves a compact green audio device.

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

Although teeming with unique wildlife – including centuries-old large turtles, marine lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain near the shoreline of Ecuador had long remained free of amphibians.

In the late 1990s, this changed. Some small amphibians traveled from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic research suggest that, over the years, there have been multiple accidental introductions to the archipelago, and the frogs now have a strong presence on several locations: Isabela and Santa Cruz.

The population is expanding so rapidly that researchers have been finding it difficult to monitor, estimating numbers in the millions on every island, across urban and agricultural areas, but also in the protected Galápagos national park.

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

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

Deafening Noise and Rising Worries

The frogs' abundance is clear from the acoustic chaos they create. "The amount of frogs and the noise – it's truly insane," comments the scientist.

For the scientists, their nocturnal vocalizations are useful in determining their existence in far-flung areas, using audio devices like the one near the office.

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

"During 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 first frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

The noise isn't the primary problem, though. While the amphibians has been in the islands for nearly 30 years, scientists still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On islands, it is very common for invasive organisms to thrive, as they have few of their enemies. The Galápagos has 1,645 introduced types, many of which are seriously affecting the survival of its native ones.

A recent research indicates the non-native amphibians are voracious insect eaters, and might be disproportionately consuming uncommon bugs found exclusively on the archipelago, or reducing the food sources of the region's rare avian species, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some atypical characteristics, including surviving in brackish water, which is uncommon for frogs.

Their development stage is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a long time: San José observed one which stayed as a larva in her laboratory 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 resource in the islands.

Techniques to curb the frogs in the beginning of the century were mostly ineffective. Conservation officers tried collecting large numbers by hand and slowly raising the salt content of lagoons in without success.

Research indicates applying caffeine – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't necessarily safe for other rare Galápagos species.

Lacking answers to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she hopes the growing use of environmental DNA methods and DNA examination will assist her team make sense of the invasive species, funding for the project has been difficult to come by.

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