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On her daily walk to the scientific station, biologist Miriam San José crouches near a shallow pond surrounded by dense plants and collects a compact plastic sound recorder.

She had placed there through the night to record the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an non-native threat with consequences that scientists are just beginning to understand.

Despite abounding with remarkable wildlife – such as ancient giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's evolutionary theory – the island chain off the coast of Ecuador had long remained free of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from continental Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic research suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the frogs now have a firm foothold on several locations: Isabela and Santa Cruz.

The numbers is growing so quickly that scientists have been struggling to keep track, calculating numbers in the millions on every island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the subsequent 10 days, she could find just one tagged frog occasionally, indicating their populations were massive.

They estimated six thousand frogs in a single pond. "The calculations are still very conservative," says the researcher. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' proliferation is evident from the sound chaos they create. "The amount of frogs and the noise – it's truly incredible," comments the scientist.

For the researchers, their nocturnal mating calls are helpful in estimating their presence in remote areas, using recorders like the one near San José's office.

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

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

"At first 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 leaped on her palm as she was stepping out of her house.

Ecological Impact Remains Unknown

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

On archipelagos, it is very common for invasive species to thrive, as they have none of their enemies. The Galápagos has over sixteen hundred invasive types, many of which are seriously affecting the safety of its endemic ones.

A recent research indicates the invasive frogs are hungry bug consumers, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or reducing the nutrition of the region's rare avian species, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also extremely variable, with some larvae becoming frogs very quickly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for half a year.

"We truly don't know this part," she says, concerned the tadpoles could be affecting the region's freshwater, a very scarce resource in Galápagos.

Methods to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried capturing large numbers by manual methods and gradually raising the salt content of lagoons in vain.

Research suggests applying coffee – which is highly poisonous to amphibians – or using electrocution could help, but these approaches aren't always secure for other rare Galápagos species.

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

Financial Obstacles for Study

While she expects the growing use of environmental DNA techniques and DNA examination will help her team understand of the invader, funding for the research has been hard to come by.

"Everyone wants to give funding for protecting frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to control."