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During her daily commute to the scientific station, scientist Miriam San José stoops near a shallow pond covered by dense vegetation and collects a compact plastic sound recorder.

She had placed there through the night to record the distinctive calls of the Fowler's snouted treefrog, known by local researchers as an invasive threat with effects that scientists are just beginning to understand.

Although abounding with unique animals – such as ancient large turtles, swimming lizards, and the famous birds that sparked Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been free of frogs and toads.

During the 1990s, this shifted. Some small amphibians traveled from mainland Ecuador to the islands, likely as hitchhikers on cargo ships.

DNA research indicate that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a strong presence on several islands: multiple locations.

The numbers 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 agricultural areas, but also in the protected Galápagos national park.

When San José tagged amphibians and attempted to find them in the subsequent week and a half, she could find just one marked frog occasionally, indicating their populations were enormous.

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

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly mating calls are useful in determining their presence in remote areas, using recorders like the one near the office.

But nearby farmers say the sounds are so raucous they keep them up at night.

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

"Initially it was a shock, observing the first frogs in the region," says the farmer, who started noticing their abundance about several years ago when one jumped on her palm as she was walking out of her front door.

Ecological Impact Remains Unclear

The sound isn't the primary problem, however. While the amphibians has been in the Galápagos for almost three decades, scientists still know very little about its effect on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very common for invasive species to prosper, as they have none of their enemies. The Galápagos counts 1,645 invasive types, many of which are significantly disrupting the survival of its native ones.

A recent study suggests the non-native frogs are hungry bug eaters, and might be disproportionately eating uncommon bugs found only on the archipelago, or reducing the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The island frogs have shown some atypical traits, including living in brackish water, which is rare for frogs.

Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which stayed as a tadpole in her laboratory for six months.

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

Techniques to control the amphibians in the beginning of the century were mostly ineffective. Conservation officers tried collecting large numbers by manual methods and gradually increasing the salt content of lagoons in vain.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrical methods could help, but these methods aren't necessarily safe for other uncommon Galápagos organisms.

Lacking solutions to more of the basic questions about their biology and impact, removing the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she expects the growing use of eDNA methods and DNA analysis will assist her team make sense of the invasive species, funding for the research has been hard to obtain.

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