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During her daily commute to the research facility, biologist the researcher crouches near a small pond covered by thick vegetation and collects a small green sound recorder.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive species with effects that experts are just beginning to comprehend.

Despite teeming with remarkable animals – including centuries-old giant tortoises, marine iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had historically been free of amphibians.

During the 1990s, this shifted. Several small tree frogs made their way from continental Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA research indicate that, through time, there have been repeated unintentional arrivals to the archipelago, and the amphibians now have a strong presence on two islands: Isabela and Santa Cruz.

The numbers is expanding so quickly that scientists have been struggling to monitor, calculating numbers in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When the biologist marked frogs and attempted to find them in the following week and a half, she could find only a single tagged frog from time to time, indicating their populations were massive.

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

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the sound disruption they cause. "The number of frogs and the noise – it's really insane," says San José.

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

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

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

"At first it was a surprise, seeing the first frogs in the region," says the farmer, who started observing their large numbers about three years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Remains Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for almost 30 years, experts still know very little about its impact on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive species to thrive, as they have few of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are seriously disrupting the safety of its native ones.

A 2020 study indicates the invasive frogs are hungry insect consumers, and might be unevenly consuming uncommon insects found exclusively on the islands, or reducing the nutrition of the islands' uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have exhibited some atypical characteristics, including surviving in slightly salty water, which is rare for amphibians.

Their development stage is also highly inconsistent, with some tadpoles becoming frogs very quickly and others taking a extended period: the researcher witnessed one which remained as a tadpole in her laboratory for half a year.

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

Methods to curb the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried capturing large numbers by hand and slowly increasing the salt content of lagoons in vain.

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

Lacking answers to more of the basic questions about their biology and effect, culling the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Research

While she hopes the growing use of eDNA techniques and DNA analysis will assist her group understand of the invasive species, funding for the research has been hard to obtain.

"Everybody wants to give funding for protecting frogs," says San José. "But it's more difficult to find financial backing for an introduced frog that you might want to control."