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During her daily walk to the research facility, biologist the researcher stoops near a small pond covered by thick vegetation and retrieves a compact green audio recorder.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that scientists are just beginning to understand.

Although teeming with unique wildlife – such as ancient giant tortoises, swimming lizards, and the famous birds that inspired Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained free of amphibians.

In the late 1990s, this changed. Some small amphibians traveled from continental the mainland to the islands, likely as hitchhikers on transport vessels.

Genetic research indicate that, over the years, there have been multiple accidental arrivals to the islands, and the frogs now have a strong foothold on two locations: multiple locations.

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

When the biologist marked frogs and attempted to recapture them in the subsequent 10 days, she could find just one marked frog occasionally, indicating their numbers were enormous.

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," says San José. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' proliferation is clear from the acoustic disruption they create. "The amount of frogs and the noise – it's truly incredible," says the scientist.

For the scientists, their nocturnal vocalizations are helpful in estimating their existence in remote areas, using recorders like the one near San José's workplace.

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

"In the wet season, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, seeing the initial frogs in the area," says the farmer, who started observing 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 Unclear

The sound isn't the primary problem, however. While the species has been in the islands for nearly three decades, experts still know very little about its effect 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 natural predators. The Galápagos counts over sixteen hundred invasive types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 research indicates the invasive amphibians are voracious insect consumers, and might be unevenly consuming rare insects found exclusively on the islands, or depleting the nutrition of the region's rare avian species, disrupting the food chain.

Unusual Traits and Control Challenges

The island frogs have exhibited some atypical characteristics, including surviving in brackish water, which is rare for amphibians.

Their development stage is also extremely variable, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her lab for half a year.

"We truly don't know this aspect," she says, worried the larvae could be affecting the region's freshwater, a very scarce commodity in the islands.

Techniques to control the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried collecting large numbers by manual methods and slowly raising the salt content of ponds in without success.

Studies suggests spraying coffee – which is highly poisonous to amphibians – or using electrocution could help, but these methods aren't always secure for other uncommon Galápagos organisms.

Lacking solutions to more of the fundamental issues about their biology and impact, 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 environmental DNA methods and genetic examination will assist her team understand of the invasive species, financial support for the research has been difficult to obtain.

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