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On her regular walk to the research facility, biologist Miriam San José stoops near a shallow pond covered by dense vegetation and collects a compact green sound recorder.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with effects that scientists are starting to comprehend.

Although teeming with unique wildlife – such as centuries-old large turtles, swimming lizards, and the well-known finches that sparked Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had long remained devoid of amphibians.

During the 1990s, this shifted. Some tiny amphibians traveled from continental Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic research indicate that, through time, there have been repeated accidental introductions to the islands, and the frogs now have a strong presence on two islands: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the subsequent week and a half, she could locate only a single tagged frog from time to time, indicating their populations were massive.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the sound disruption they cause. "The amount of frogs and the sound – it's truly insane," comments San José.

For the scientists, their nocturnal mating calls are useful in determining 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.

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

"At first it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started observing their abundance about three years ago when one leaped on her palm as she was stepping out of her house.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the amphibians has been in the islands for almost 30 years, experts still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive organisms to prosper, as they have none of their enemies. The islands counts 1,645 invasive types, many of which are seriously affecting the safety of its native ones.

A 2020 study indicates the invasive amphibians are voracious insect consumers, and might be disproportionately eating uncommon insects found only on the islands, or depleting the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: San José 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 tadpoles could be affecting the islands' clean water, a very scarce commodity in the islands.

Methods to curb the amphibians in the beginning of the century were mostly ineffective. Conservation officers tried collecting large numbers by hand and gradually raising the salinity of lagoons in without success.

Research indicates applying caffeine – which is highly toxic to frogs – or using electrocution could assist, but these methods aren't always secure for other uncommon Galápagos species.

Without solutions to more of the basic questions about their biology and effect, culling the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will assist her team understand of the invader, financial support for the research has been hard to come by.

"Everybody wants to give funding for protecting frogs," says the researcher. "But it's harder to find financial backing for an introduced frog that you might want to control."