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On her daily walk to the research facility, biologist the researcher crouches near a small water body surrounded by thick plants and collects a small plastic audio recorder.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, known by Galápagos scientists as an non-native species with effects that experts are just beginning to comprehend.

Despite teeming with remarkable animals – including ancient large turtles, marine lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the island chain off the shoreline of Ecuador had historically been free of amphibians.

In the late 1990s, this changed. Several small tree frogs traveled from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA research suggest that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong presence on two islands: multiple locations.

The population is expanding so quickly that researchers have been struggling to monitor, estimating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the protected Galápagos national park.

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

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

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the acoustic chaos they cause. "The number of frogs and the noise – it's really incredible," says the scientist.

For the researchers, their nightly mating calls are helpful in determining their existence in remote areas, using recorders like the one near San José's workplace.

But local farmers say the sounds are so loud they prevent sleep at night.

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

"At first it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for almost three decades, experts still know limited information about its effect on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very typical for non-native organisms to prosper, as they have few of their natural predators. The islands has over sixteen hundred introduced species, many of which are seriously affecting the safety of its native ones.

A recent study suggests the non-native amphibians are voracious insect consumers, and might be disproportionately consuming rare bugs found exclusively on the archipelago, or reducing the nutrition of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

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

Their metamorphosis stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José witnessed one which stayed as a larva in her laboratory for six months.

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

Techniques to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried collecting significant quantities by hand and gradually raising the salt content of lagoons in without success.

Research indicates applying coffee – which is highly poisonous to amphibians – or using electrical methods could assist, but these methods aren't always secure for other uncommon island species.

Lacking solutions to more of the basic questions about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says San José.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and DNA examination will assist her team make sense of the invader, financial support for the research has been hard to come by.

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