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On her regular walk to the scientific station, scientist Miriam San José stoops near a shallow pond surrounded by thick vegetation and retrieves a compact plastic audio device.

The device was left there through the night to capture the characteristic calls of the Scinax quinquefasciatus, known by Galápagos scientists as an invasive species with consequences that experts are starting to understand.

Although abounding with unique wildlife – such as centuries-old giant tortoises, marine lizards, and the famous birds that inspired Charles Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained free of frogs and toads.

During the 1990s, this shifted. Some small amphibians made their way from continental the mainland to the islands, likely as hitchhikers on transport vessels.

Genetic research indicate that, over the years, there have been repeated accidental introductions to the islands, and the amphibians now have a firm presence on several islands: multiple locations.

The population is expanding so quickly that researchers have been struggling to monitor, estimating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the protected natural reserve.

When San José marked amphibians and attempted to recapture them in the following 10 days, she could find just one marked frog occasionally, indicating their numbers were enormous.

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

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the sound chaos they cause. "The amount of frogs and the sound – it's really incredible," says the scientist.

For the scientists, their nocturnal mating calls are helpful in estimating their presence in far-flung areas, using audio devices like the one near the office.

But local farmers say the sounds are so raucous 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.

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started noticing their large numbers about three years ago when one jumped on her hand as she was stepping out of her front door.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, though. While the species has been in the islands for almost three decades, experts still know limited information about its impact on the archipelago's precariously balanced land and water environments.

On islands, it is very common for non-native organisms to thrive, as they have few of their natural predators. The Galápagos has 1,645 introduced types, many of which are significantly affecting the survival of its endemic ones.

A recent study suggests the invasive frogs are voracious bug eaters, and might be unevenly consuming uncommon bugs found exclusively on the islands, or reducing the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have shown some atypical traits, including living in slightly salty water, which is rare for amphibians.

Their development process is also highly variable, with some tadpoles turning into frogs very rapidly and others taking a extended period: the researcher observed one which remained as a larva in her lab for six months.

"We truly 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 early 2000s were mostly unsuccessful. Park rangers tried capturing large numbers by hand and slowly increasing the salt content of ponds in without success.

Research indicates spraying caffeine – which is extremely toxic to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon island organisms.

Lacking solutions to more of the basic issues about their biology and impact, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she expects the increasing use of eDNA techniques and genetic examination will help her group understand of the invader, financial support for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."