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On her regular commute to the research facility, scientist Miriam San José crouches near a small water body surrounded by dense vegetation and retrieves a compact plastic sound recorder.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by local scientists as an non-native species with consequences that experts are starting to understand.

Despite teeming with remarkable wildlife – such as centuries-old large turtles, marine iguanas, and the well-known finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of Ecuador had long remained free of amphibians.

In the late 1990s, this changed. Several tiny tree frogs traveled from mainland the mainland to the islands, likely as stowaways on transport vessels.

DNA studies suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a strong foothold on several locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that researchers have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the subsequent week and a half, she could locate just one tagged frog from time to time, indicating their populations were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very low," states San José. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the acoustic disruption they create. "The number of frogs and the noise – it's really incredible," comments the scientist.

For the researchers, their nightly mating calls are useful in estimating their presence in remote areas, using recorders like the one near the workplace.

But local agricultural workers say the sounds are so raucous they prevent sleep at night.

"In the wet season, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a surprise, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about several years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the species has been in the Galápagos for nearly 30 years, experts still know limited information about its effect on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very typical for invasive species to thrive, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are seriously affecting the safety of its endemic ones.

A recent study indicates the non-native frogs are voracious bug consumers, and might be unevenly consuming uncommon insects found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some unusual traits, including living in brackish water, which is rare for frogs.

Their metamorphosis process is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a long time: San José observed one which stayed as a larva in her laboratory for half a year.

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

Techniques to curb the frogs in the early 2000s were largely ineffective. Conservation officers tried capturing significant quantities by hand and gradually increasing the salinity of lagoons in without success.

Research indicates applying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these approaches aren't necessarily secure for other uncommon Galápagos species.

Without solutions to more of the fundamental questions about their biology and impact, culling the frogs might not even be the right way to proceed, says San José.

Financial Obstacles for Study

While she expects the growing use of environmental DNA techniques and DNA analysis will help her team make sense of the invader, financial support for the project has been difficult to obtain.

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