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On her regular walk to the research facility, scientist the researcher crouches near a shallow pond surrounded by thick plants and collects a small plastic audio device.

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

Although teeming with unique animals – such as ancient giant tortoises, marine lizards, and the well-known finches that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had long remained devoid of amphibians.

In the late 1990s, this shifted. Some small amphibians made their way from continental the mainland to the islands, probably as stowaways on cargo ships.

DNA studies suggest that, through time, there have been repeated accidental introductions to the islands, and the amphibians now have a firm presence on two islands: Isabela and Santa Cruz.

The numbers is expanding so rapidly that researchers have been finding it difficult to monitor, calculating populations in the millions on every island, across urban and farming areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to find them in the following 10 days, she could locate only a single marked frog occasionally, indicating their populations were massive.

They calculated six thousand frogs in a single pond. "The calculations are still very low," states the researcher. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly vocalizations are helpful in estimating their existence in remote areas, using audio devices like the one outside San José's office.

But local farmers say the sounds are so raucous they keep them up at night.

"In the wet season, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from the island.

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

Environmental Consequences Stays Unknown

The noise 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 effect on the islands' delicately balanced land and water ecosystems.

On islands, it is very typical for non-native organisms to thrive, as they have none of their natural predators. The islands counts 1,645 introduced species, many of which are significantly disrupting the survival of its native ones.

A recent research suggests the invasive amphibians are voracious bug consumers, and might be disproportionately eating uncommon bugs found exclusively on the archipelago, or reducing the nutrition of the islands' uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a long time: 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 larvae could be impacting the region's freshwater, a very scarce resource in Galápagos.

Techniques to curb the frogs in the early 2000s were mostly ineffective. Conservation officers tried capturing significant quantities by manual methods and slowly raising the salinity of lagoons in without success.

Studies suggests spraying caffeine – which is highly toxic to frogs – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos organisms.

Lacking solutions to more of the basic issues about their biology and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she expects the growing use of environmental DNA techniques and genetic examination will assist her group make sense of the invasive species, funding for the project has been difficult to obtain.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to manage."