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During her daily walk to the research facility, biologist the researcher stoops near a small water body surrounded by thick vegetation and retrieves a compact green audio recorder.

She had placed there overnight to record the distinctive calls of the Scinax quinquefasciatus, known by local scientists as an non-native threat with consequences that scientists are just beginning to comprehend.

Although abounding with remarkable animals – including centuries-old giant tortoises, marine iguanas, and the well-known birds that inspired Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been free of frogs and toads.

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

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

The population is growing so rapidly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to recapture them in the following week and a half, she could locate just one tagged frog from time to time, suggesting their numbers were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic disruption they create. "The amount of frogs and the noise – it's truly insane," comments the scientist.

For the scientists, their nocturnal vocalizations are helpful in determining their presence in far-flung areas, using recorders like the one outside the workplace.

But local agricultural workers say the sounds are so raucous they keep them up at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

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

On archipelagos, it is very typical for non-native species to prosper, as they have none of their natural predators. The Galápagos has 1,645 introduced species, many of which are significantly disrupting the safety of its endemic ones.

A recent research indicates the invasive amphibians are hungry bug consumers, and might be unevenly consuming rare insects found only on the islands, or reducing the nutrition of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos amphibians have exhibited some atypical traits, including surviving in slightly salty water, which is uncommon for amphibians.

Their development stage is also highly variable, with some larvae turning into frogs very quickly and others taking a extended period: the researcher observed one which stayed as a larva in her laboratory for half a year.

"We really don't know this aspect," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited commodity in the islands.

Methods to control the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly raising the salt content of lagoons in without success.

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

Lacking solutions to more of the basic questions about their biology and effect, culling the frogs 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 DNA examination will assist her team make sense of the invasive species, financial support for the project has been hard to obtain.

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