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On her regular commute to the scientific station, biologist the researcher stoops near a small water body surrounded by dense vegetation and collects a compact plastic sound device.

She had placed there through the night to record the characteristic croaks of the Scinax quinquefasciatus, known by local researchers as an non-native threat with consequences that experts are just beginning to comprehend.

Although abounding with unique animals – including ancient large turtles, swimming lizards, and the famous finches that inspired Charles Darwin's evolutionary theory – the island chain near the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this changed. Several small tree frogs made their way from continental Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research indicate that, through time, there have been repeated accidental arrivals to the archipelago, and the amphibians now have a firm foothold on two islands: Isabela and Santa Cruz.

The numbers is expanding so quickly that researchers have been struggling to keep track, estimating populations in the millions on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged amphibians and attempted to find them in the following week and a half, she could locate only a single tagged frog occasionally, suggesting their populations were massive.

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

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the acoustic chaos they create. "The number of frogs and the sound – it's really incredible," says San José.

For the scientists, their nightly vocalizations are useful in determining their existence in remote areas, using recorders like the one near the workplace.

But nearby agricultural workers say the sounds are so loud they prevent sleep at night.

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

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

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly 30 years, experts still know very little about its impact on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

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

A 2020 research indicates the non-native frogs are hungry bug eaters, and might be unevenly consuming rare insects found only on the islands, or reducing the food sources of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

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

Their development stage is also extremely variable, with some tadpoles turning into frogs very quickly and others taking a long time: San José witnessed one which remained as a larva in her lab for half a year.

"We truly don't know this part," she says, concerned the larvae could be impacting the islands' freshwater, a very limited commodity in the islands.

Methods to control the frogs in the early 2000s were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly raising the salt content of ponds in vain.

Studies suggests applying coffee – which is highly toxic to frogs – or using electrical methods could assist, but these approaches aren't always safe for other rare island species.

Lacking answers to more of the basic issues about their lifestyle and effect, removing the frogs might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she expects the growing use of eDNA techniques and DNA analysis will help her group understand of the invasive species, financial support for the project has been difficult to come by.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's harder to find funding for an invasive frog that you might want to manage."