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During her daily walk to the scientific station, scientist the researcher stoops near a small water body covered by thick vegetation and collects a compact plastic audio recorder.

The device was left there overnight to record the characteristic calls of the Scinax quinquefasciatus, recognized by local scientists as an non-native species with effects that experts are starting to understand.

Despite abounding with remarkable wildlife – such as centuries-old large turtles, marine iguanas, and the famous birds that inspired Charles Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had historically been free of frogs and toads.

In the late 1990s, this changed. Some tiny amphibians made their way from continental Ecuador to the islands, likely as hitchhikers on transport vessels.

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

The numbers is growing so rapidly that researchers have been struggling to monitor, estimating populations in the millions on each island, across urban and agricultural 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 locate only a single tagged frog from time to time, indicating their populations were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the acoustic chaos they cause. "The number of frogs and the noise – it's truly incredible," comments San José.

For the scientists, their nocturnal vocalizations are helpful in determining their presence in far-flung areas, using audio devices like the one near San José's workplace.

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

"During the wet season, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, observing the first frogs in the region," says the farmer, who started observing 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 noise isn't the fundamental problem, though. While the amphibians has been in the islands for almost 30 years, experts still know very little about its effect on the archipelago's precariously balanced land and water environments.

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

A recent study suggests the non-native amphibians are voracious insect eaters, and might be unevenly consuming uncommon bugs found exclusively on the archipelago, or reducing the nutrition of the islands' uncommon birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos frogs have exhibited some unusual traits, including living in slightly salty water, which is uncommon for frogs.

Their development stage is also extremely inconsistent, with some larvae becoming frogs very rapidly and others taking a long time: the researcher observed one which stayed as a larva in her lab for six months.

"We truly don't know this aspect," she says, worried the larvae could be impacting the islands' freshwater, a very limited commodity in Galápagos.

Techniques to curb the amphibians in the early 2000s were largely ineffective. Park rangers tried collecting large numbers by hand and gradually increasing the salinity of ponds in without success.

Research suggests applying caffeine – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't necessarily secure for other rare island organisms.

Lacking solutions to more of the fundamental issues about their biology and impact, culling the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA methods and genetic analysis will help her group understand of the invader, financial support for the research has been hard to obtain.

"Everyone wants to give funding for protecting frogs," says the researcher. "But it's harder to find funding for an introduced frog that you might want to manage."