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During her daily commute to the scientific station, biologist the researcher stoops near a small pond covered by dense vegetation and collects a small green sound recorder.

The device was left there overnight to record the characteristic croaks of the Fowler's snouted treefrog, recognized by local researchers as an invasive species with consequences that experts are starting to understand.

Despite abounding with remarkable animals – including centuries-old giant tortoises, swimming lizards, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this changed. Some small amphibians made their way from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

DNA research indicate that, over the years, there have been repeated unintentional arrivals to the archipelago, and the frogs now have a firm presence on two islands: Isabela and Santa Cruz.

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

When San José marked amphibians and attempted to find them in the following week and a half, she could find only a single marked frog from time to time, indicating their numbers were massive.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

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

For the researchers, their nightly vocalizations are useful in determining their existence in far-flung areas, using audio devices like the one outside San José's office.

But nearby farmers say the sounds are so raucous they prevent sleep at night.

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

"At first it was a shock, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their large numbers about three years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Remains Unknown

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

On archipelagos, it is very common for non-native species to prosper, as they have none of their enemies. The islands has over sixteen hundred introduced species, many of which are seriously disrupting the survival of its endemic ones.

A recent study suggests the non-native frogs are voracious insect eaters, and might be unevenly eating rare bugs found exclusively on the islands, or reducing the food sources of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: San José witnessed one which stayed as a tadpole in her lab for half a year.

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

Techniques to control the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and slowly raising the salt content of lagoons in vain.

Studies suggests applying caffeine – which is highly poisonous to frogs – or using electrocution could assist, but these methods aren't necessarily safe for other rare Galápagos organisms.

Lacking answers to more of the fundamental issues about their lifestyle and impact, culling the amphibians might not even be the correct way to proceed, says San José.

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will assist her group understand of the invader, funding for the project has been hard to come by.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."