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During her daily walk to the scientific station, scientist Miriam San José crouches near a shallow water body covered by thick vegetation and retrieves a compact plastic audio device.

She had placed there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native threat with consequences that experts are just beginning to comprehend.

Although abounding with unique animals – including ancient giant tortoises, marine lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs traveled from mainland Ecuador to the islands, probably as stowaways on cargo ships.

DNA research indicate that, through time, there have been repeated accidental arrivals to the islands, and the frogs now have a strong foothold on several islands: multiple locations.

The population is expanding so quickly 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 Galápagos national park.

When the biologist tagged amphibians and attempted to recapture them in the subsequent 10 days, she could find only a single marked frog occasionally, indicating their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is evident from the acoustic disruption they cause. "The number of frogs and the sound – it's really incredible," says the scientist.

For the researchers, their nocturnal mating calls are useful in determining their existence in remote areas, using recorders like the one near San José's workplace.

But nearby farmers say the sounds are so raucous they keep them up at night.

"In the rainy period, I constantly hear their croaks and they're really loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly three decades, experts still know limited information about its impact on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very typical for non-native species to thrive, as they have none of their enemies. The islands has 1,645 introduced species, many of which are seriously disrupting the survival of its native ones.

A recent study suggests the invasive frogs are hungry insect eaters, and might be unevenly consuming rare bugs found exclusively on the archipelago, or reducing the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also highly variable, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher observed one which stayed as a tadpole in her laboratory for six months.

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

Methods to control the frogs in the beginning of the century were largely ineffective. Park rangers tried collecting large numbers by manual methods and slowly increasing the salinity of ponds in without success.

Research indicates applying caffeine – which is extremely poisonous to amphibians – or using electrocution could help, but these methods aren't necessarily secure for other rare Galápagos species.

Without solutions to more of the fundamental issues about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will help her group make sense of the invader, financial support for the research has been difficult to come by.

"Everyone wants to give funding for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to manage."