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On her regular walk to the research facility, scientist Miriam San José stoops near a shallow water body surrounded by thick vegetation and retrieves a small green audio device.

The device was left there overnight to record the characteristic calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native species with effects that experts are just beginning to understand.

Despite abounding with unique animals – such as centuries-old giant tortoises, swimming iguanas, and the famous birds that sparked Charles Darwin's evolutionary theory – the island chain near the coast of South America had historically been devoid of amphibians.

During the 1990s, this changed. Some small tree frogs made their way from mainland Ecuador to the archipelago, likely as stowaways on transport vessels.

DNA research indicate that, through time, there have been multiple accidental introductions to the archipelago, and the amphibians now have a strong presence on several islands: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been struggling to monitor, estimating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation natural reserve.

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

They calculated 6,000 frogs in a single pond. "Our estimates are still very low," states the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

The amphibians' abundance is clear from the sound disruption they cause. "The number of frogs and the noise – it's truly incredible," comments San José.

For the scientists, their nightly mating calls are helpful in determining their presence in far-flung areas, using audio devices like the one near San José's 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 calls and they're really loud," says Jadira Larrea Saltos from the island.

"Initially it was a shock, observing the first frogs in the region," says Larrea Saltos, who started noticing their large numbers about three years ago when one leaped on her hand as she was stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, though. While the amphibians has been in the islands for nearly three decades, scientists still know limited information about its impact on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very typical for invasive organisms to thrive, as they have few of their natural predators. The islands counts 1,645 invasive types, many of which are seriously disrupting the safety of its native ones.

A recent research suggests the invasive amphibians are voracious bug consumers, and might be unevenly consuming rare bugs found only on the islands, or reducing the food sources of the islands' rare avian species, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some atypical characteristics, including living in slightly salty water, which is uncommon for amphibians.

Their development process is also extremely variable, with some larvae becoming frogs very rapidly and others taking a long time: San José observed one which remained as a tadpole in her lab for six months.

"We really don't know this part," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited resource in the islands.

Methods to control the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried capturing large numbers by hand and gradually increasing the salt content of ponds in vain.

Studies indicates applying coffee – which is highly poisonous to frogs – or using electrocution could help, but these methods aren't necessarily safe for other rare Galápagos species.

Lacking answers to more of the fundamental questions about their biology and impact, removing the frogs might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she hopes the growing use of eDNA methods and genetic analysis will help her team understand of the invasive species, financial support for the project has been hard to come by.

"Everybody 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."