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During her regular walk to the scientific station, scientist the researcher crouches near a shallow water body covered by dense vegetation and collects a compact plastic sound recorder.

She had placed there overnight to capture the distinctive calls of the Scinax quinquefasciatus, known by Galápagos researchers as an non-native species with consequences that experts are just beginning to comprehend.

Although teeming with unique animals – such as ancient large turtles, marine iguanas, and the famous birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of Ecuador had long remained devoid of amphibians.

In the late 1990s, this changed. Several tiny tree frogs traveled from continental Ecuador to the archipelago, probably as stowaways on transport vessels.

Genetic research indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the frogs now have a firm foothold on two locations: multiple locations.

The numbers is expanding so rapidly that researchers have been finding it difficult to keep track, calculating numbers in the millions on each island, across urban and farming areas, but also in the protected Galápagos national park.

When San José tagged frogs and attempted to recapture them in the following week and a half, she could locate only a single tagged frog occasionally, indicating their numbers were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I am pretty sure there are even more."

Deafening Noise and Growing Concerns

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

For the researchers, their nightly mating calls are helpful in estimating their existence in remote areas, using recorders like the one near the office.

But nearby agricultural workers say the sounds are so loud they keep them up at night.

"In the rainy period, I regularly hear their calls and they're extremely loud," says a local coffee farmer from the island.

"Initially it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, however. While the amphibians has been in the islands for almost 30 years, scientists still know very little about its impact on the archipelago's precariously balanced land and water environments.

On islands, it is very common for invasive organisms to prosper, as they have few of their natural predators. The islands has over sixteen hundred invasive species, many of which are seriously affecting the safety of its native ones.

A 2020 research indicates the invasive amphibians are voracious insect eaters, and might be unevenly eating rare insects found only on the archipelago, or reducing the nutrition of the islands' uncommon birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The island amphibians have exhibited some unusual characteristics, including living in brackish water, which is rare for amphibians.

Their development stage is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher observed one which remained as a tadpole in her lab for six months.

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

Techniques to control the amphibians in the early 2000s were largely unsuccessful. Conservation officers tried collecting large numbers by hand and slowly increasing the salt content of lagoons in vain.

Studies suggests applying coffee – which is highly toxic to frogs – or using electrocution could help, but these methods aren't necessarily safe for other uncommon Galápagos organisms.

Without solutions to more of the fundamental issues about their lifestyle and effect, culling the frogs might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Research

While she expects the increasing use of eDNA methods and DNA examination will help her group make sense of the invader, funding for the research has been hard to obtain.

"Everybody 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 manage."