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On her daily walk to the research facility, scientist Miriam San José stoops near a small pond covered by thick vegetation and retrieves a small green sound recorder.

She had placed there overnight to record the distinctive croaks of the Scinax quinquefasciatus, known by local scientists as an non-native threat with effects that experts are starting to understand.

Although abounding with remarkable animals – such as ancient large turtles, marine iguanas, and the well-known finches that sparked Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained free of frogs and toads.

In the late 1990s, this changed. Several small tree frogs made their way from mainland Ecuador to the islands, probably as hitchhikers on transport vessels.

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

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

When the biologist marked frogs and attempted to find them in the subsequent week and a half, she could locate only a single marked frog from time to time, indicating their populations were enormous.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states the researcher. "I am quite certain there are even more."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly vocalizations are helpful in estimating their existence in remote areas, using recorders like the one outside San José's workplace.

But nearby agricultural workers say the calls are so raucous they keep them up at night.

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

"Initially it was a surprise, seeing the first frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her hand as she was stepping out of her house.

Ecological Impact Remains Unclear

The noise isn't the primary problem, though. While the amphibians has been in the Galápagos for almost three decades, experts still know very little about its effect on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very common for non-native organisms to prosper, as they have none of their natural predators. The islands counts over sixteen hundred invasive species, many of which are seriously disrupting the survival of its endemic ones.

A recent research indicates the invasive frogs are voracious insect consumers, and might be disproportionately eating uncommon insects found exclusively on the archipelago, or depleting the nutrition of the region's rare birds, affecting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some unusual characteristics, including living in slightly salty water, which is rare for amphibians.

Their development stage is also highly inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a larva in her lab for six months.

"We truly don't know this aspect," she says, worried the larvae could be impacting the islands' freshwater, a very limited resource in the islands.

Techniques to curb the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting significant quantities by hand and slowly raising the salt content of ponds in vain.

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

Without solutions to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Study

While she hopes the growing use of environmental DNA methods and genetic analysis will help her group make sense of the invasive species, financial support for the project has been hard to obtain.

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