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During her regular commute to the research facility, biologist the researcher crouches near a shallow water body covered by thick vegetation and collects a compact plastic audio recorder.

She had placed there overnight to capture the distinctive croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive threat with effects that scientists are starting to understand.

Although abounding with remarkable animals – including ancient large turtles, marine iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained free of amphibians.

In the late 1990s, this changed. Several small amphibians made their way from mainland Ecuador to the islands, probably as stowaways on cargo ships.

DNA studies suggest that, over the years, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm foothold on several locations: Isabela and Santa Cruz.

The numbers is growing so rapidly that scientists have been finding it difficult to keep track, calculating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to recapture them in the following week and a half, she could find just one marked frog occasionally, indicating their populations were enormous.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they create. "The number of frogs and the noise – it's truly insane," says San José.

For the researchers, their nocturnal vocalizations are helpful in determining their presence in remote areas, using audio devices like the one outside the office.

But nearby agricultural workers say the calls are so raucous they prevent sleep at night.

"In the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

"Initially it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started observing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unknown

The noise isn't the primary problem, though. While the amphibians has been in the islands for almost three decades, experts still know very little about its impact on the islands' precariously balanced land and water ecosystems.

On islands, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos counts 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A recent study indicates the non-native frogs are hungry insect consumers, and might be unevenly eating rare bugs found exclusively on the islands, or reducing the nutrition of the region's uncommon avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have exhibited some atypical traits, including surviving in brackish water, which is uncommon for frogs.

Their development stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José witnessed one which remained as a larva in her lab for six months.

"We truly don't know this aspect," she says, worried the larvae could be impacting the islands' freshwater, a very limited commodity in the islands.

Techniques to control the frogs in the early 2000s were largely ineffective. Conservation officers tried capturing large numbers by hand and gradually increasing the salt content of ponds in without success.

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

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

Funding Challenges for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will assist her team make sense of the invasive species, financial support for the project has been difficult to obtain.

"Everybody wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to manage."