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On her regular commute to the scientific station, scientist Miriam San José crouches near a small pond surrounded by dense vegetation and retrieves a small green audio device.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive threat with effects that experts are just beginning to understand.

Despite abounding with unique wildlife – such as ancient large turtles, marine lizards, and the well-known finches that inspired Darwin's evolutionary theory – the island chain near the shoreline of South America 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, likely as stowaways on cargo ships.

DNA research indicate that, through time, there have been repeated accidental arrivals to the archipelago, and the amphibians now have a strong presence on two locations: multiple locations.

The numbers is growing so quickly that researchers have been finding it difficult to monitor, calculating populations in the millions on every island, across developed and farming areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to find them in the following 10 days, she could find just one marked frog occasionally, indicating their populations were massive.

They estimated six thousand frogs in a single pond. "The calculations are still very low," says San José. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the acoustic disruption they cause. "The number of frogs and the sound – it's truly insane," comments the scientist.

For the scientists, their nocturnal vocalizations are helpful in estimating their existence in remote areas, using recorders like the one outside the office.

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

"In the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from the island.

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

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its impact on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very typical for invasive organisms to prosper, as they have few of their natural predators. The Galápagos counts 1,645 introduced types, many of which are significantly disrupting the survival of its endemic ones.

A recent research suggests the non-native amphibians are hungry bug consumers, and might be unevenly eating uncommon insects found exclusively on the archipelago, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

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

Their development process is also extremely inconsistent, with some larvae becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which stayed as a tadpole in her lab for six months.

"We really don't know this part," she says, worried the tadpoles could be affecting the islands' clean water, a very scarce commodity in Galápagos.

Methods to control the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually raising the salinity of lagoons in without success.

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

Lacking answers to more of the fundamental questions about their biology and impact, removing the amphibians might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the growing use of eDNA techniques and DNA examination will help her group make sense of the invader, funding for the project has been hard to obtain.

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