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On her regular walk to the research facility, scientist Miriam San José crouches near a small water body covered by dense plants and retrieves a compact green audio recorder.

She had placed there through the night to record the distinctive croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native species with effects that experts are just beginning to comprehend.

Although abounding with remarkable animals – such as centuries-old large turtles, swimming iguanas, and the well-known finches that inspired Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had historically been devoid of frogs and toads.

In the late 1990s, this changed. Several tiny amphibians traveled from continental Ecuador to the archipelago, likely as hitchhikers on transport vessels.

Genetic studies suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm foothold on two islands: multiple locations.

The population is growing so rapidly that researchers have been finding it difficult to monitor, calculating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the subsequent week and a half, she could find only a single marked frog from time to time, suggesting their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are even more."

Deafening Noise and Growing Concerns

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

For the researchers, their nocturnal mating calls are useful in estimating their existence in far-flung areas, using recorders like the one outside the office.

But nearby agricultural workers say the calls are so raucous they prevent sleep at night.

"In the wet season, I constantly hear their calls and they're extremely loud," says a local coffee farmer from the island.

"At first it was a shock, observing the initial frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unclear

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

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

A recent research suggests the invasive amphibians are voracious bug consumers, and might be disproportionately consuming rare bugs found only on the archipelago, or depleting the nutrition of the region's rare birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos amphibians have exhibited some unusual characteristics, including surviving in brackish water, which is uncommon for frogs.

Their metamorphosis stage is also extremely inconsistent, with some tadpoles turning into frogs very quickly and others taking a extended period: the researcher observed one which stayed as a tadpole in her lab for half a year.

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

Techniques to curb the amphibians in the beginning of the century were largely ineffective. Conservation officers tried capturing significant quantities by manual methods and slowly increasing the salinity of ponds in vain.

Research indicates applying coffee – which is highly poisonous to frogs – or using electrocution could assist, but these methods aren't always secure for other uncommon Galápagos species.

Lacking solutions to more of the basic issues about their lifestyle and impact, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

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

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