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On her regular walk to the research facility, scientist the researcher stoops near a shallow pond surrounded by dense vegetation and collects a compact green sound recorder.

The device was left there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive species with effects that experts are just beginning to understand.

Although abounding with remarkable wildlife – such as centuries-old giant tortoises, marine lizards, and the well-known finches that inspired Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained free of frogs and toads.

During the 1990s, this shifted. Several tiny amphibians made their way from mainland Ecuador to the islands, likely as stowaways on transport vessels.

Genetic studies suggest that, through time, there have been multiple unintentional introductions to the islands, and the frogs now have a strong foothold on several locations: multiple locations.

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

When the biologist marked frogs and attempted to recapture them in the subsequent 10 days, she could locate only a single tagged frog from time to time, suggesting their populations were enormous.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the sound disruption they cause. "The number of frogs and the sound – it's really insane," comments the scientist.

For the scientists, their nightly mating calls are helpful in determining their existence in remote areas, using recorders like the one near the workplace.

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

"In the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Ecological Impact Stays Unknown

The noise isn't the primary problem, though. While the species has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the islands' delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for non-native species to prosper, as they have none of their enemies. The Galápagos has over sixteen hundred invasive species, many of which are seriously affecting the survival of its endemic ones.

A recent research suggests the invasive frogs are hungry insect consumers, and might be unevenly eating uncommon bugs found only on the islands, or depleting the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos amphibians have shown some unusual traits, including surviving in brackish water, which is uncommon for frogs.

Their development stage is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her lab for half a year.

"We really don't know this aspect," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited resource in Galápagos.

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried collecting large numbers by manual methods and slowly increasing the salt content of lagoons in vain.

Studies suggests applying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these methods aren't necessarily secure for other rare Galápagos species.

Lacking answers to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she expects the growing use of eDNA techniques and genetic analysis will assist her group understand of the invader, funding for the research has been difficult to obtain.

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