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On her regular walk to the scientific station, scientist Miriam San José crouches near a shallow pond surrounded by thick vegetation and retrieves a compact plastic audio device.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native threat with consequences that experts are starting to comprehend.

Although teeming with unique animals – including ancient large turtles, swimming iguanas, and the well-known birds that sparked Darwin's evolutionary theory – the island chain near the coast of South America had long remained devoid of amphibians.

During the 1990s, this shifted. Some tiny tree frogs traveled from mainland Ecuador to the islands, probably as hitchhikers on transport vessels.

Genetic studies indicate that, through time, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm foothold on two islands: multiple locations.

The population is growing so quickly that scientists have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation natural reserve.

When San José tagged frogs and attempted to find them in the subsequent 10 days, she could find just one tagged frog from time to time, indicating their numbers were enormous.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the sound disruption they create. "The number of frogs and the sound – it's really insane," comments San José.

For the scientists, their nightly vocalizations are helpful in estimating their existence in remote areas, using recorders like the one near the workplace.

But nearby agricultural workers say the calls are so loud they keep them up at night.

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

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

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know limited information about its impact on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very common for non-native organisms to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are significantly affecting the safety of its native ones.

A recent research suggests the non-native frogs are hungry bug eaters, and might be unevenly eating uncommon insects found exclusively on the archipelago, or reducing the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: San José witnessed one which remained as a tadpole in her laboratory for six months.

"We really don't know this part," she says, worried the larvae could be impacting the region's freshwater, a very scarce resource in Galápagos.

Methods to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried collecting large numbers by hand and slowly raising the salt content of ponds in vain.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrical methods could assist, but these approaches aren't always safe for other rare Galápagos organisms.

Without solutions to more of the fundamental issues about their lifestyle and effect, culling the frogs might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she expects the growing use of environmental DNA techniques and DNA examination will assist her team make sense of the invasive species, funding for the research has been difficult to come by.

"Everyone wants to give support for preserving frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to manage."