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During her daily walk to the scientific station, biologist Miriam San José stoops near a small water body surrounded by dense vegetation and retrieves a small plastic audio device.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native threat with consequences that scientists are starting to comprehend.

Although abounding with remarkable wildlife – such as ancient large turtles, marine iguanas, and the famous birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had long remained free of frogs and toads.

During the 1990s, this shifted. Several tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

Genetic research indicate that, over the years, there have been multiple accidental introductions to the islands, and the amphibians now have a strong foothold on two locations: multiple locations.

The population is expanding so quickly that scientists have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation Galápagos national park.

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

They calculated six thousand frogs in a single pond. "Our estimates are still very conservative," says the researcher. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the sound chaos they create. "The number of frogs and the sound – it's really incredible," comments San José.

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

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

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

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

Environmental Consequences Remains Unknown

The sound isn't the primary problem, though. While the amphibians has been in the islands for nearly 30 years, scientists still know very little about its impact on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very common for non-native organisms to thrive, as they have none of their natural predators. The islands has over sixteen hundred introduced types, many of which are seriously disrupting the safety of its endemic ones.

A recent research indicates the invasive frogs are voracious insect consumers, and might be unevenly consuming rare bugs found only on the islands, or depleting the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development stage is also highly inconsistent, with some tadpoles turning into frogs very rapidly and others taking a long time: the researcher witnessed one which remained as a larva in her laboratory for six months.

"We really don't know this aspect," she says, worried the tadpoles could be impacting the region's clean water, a very scarce commodity in Galápagos.

Methods to curb the frogs in the beginning of the century were largely unsuccessful. Park rangers tried capturing significant quantities by hand and slowly raising the salinity of lagoons in without success.

Studies indicates applying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily secure for other uncommon Galápagos organisms.

Without answers to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles 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, financial support for the project has been difficult to come by.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to control."