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During her daily walk to the scientific station, scientist the researcher crouches near a small water body covered by dense plants and collects a compact plastic sound recorder.

She had placed there overnight to capture the distinctive croaks of the Scinax quinquefasciatus, recognized by local researchers as an invasive threat with effects that experts are starting to understand.

Despite abounding with remarkable animals – including centuries-old large turtles, swimming iguanas, and the famous finches that sparked Charles Darwin's evolutionary theory – the island chain near the coast of South America had long remained free of amphibians.

In the late 1990s, this shifted. Several tiny tree frogs made their way from continental Ecuador to the islands, probably as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a strong foothold on several locations: multiple locations.

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

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

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is evident from the sound chaos they create. "The number of frogs and the noise – it's truly incredible," says San José.

For the researchers, their nocturnal mating calls are useful in estimating their presence in far-flung areas, using audio devices like the one near the office.

But local farmers say the calls are so raucous they keep them up at night.

"In the rainy period, I regularly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, observing the initial frogs in the area," says Larrea Saltos, who started observing their large numbers about three years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Stays Unknown

The sound isn't the primary problem, though. While the species has been in the islands for almost 30 years, scientists still know very little about its impact on the archipelago's delicately balanced land and water environments.

On islands, it is very common for invasive organisms to thrive, as they have none of their natural predators. The islands has 1,645 invasive species, many of which are significantly affecting the survival of its native ones.

A 2020 research indicates the invasive amphibians are voracious insect eaters, and might be unevenly eating uncommon bugs found only on the archipelago, or depleting the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

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

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

"We really don't know this aspect," she says, worried the larvae could be affecting the region's clean water, a very limited commodity in the islands.

Techniques to control the frogs in the beginning of the century were mostly ineffective. Conservation officers tried capturing significant quantities by hand and gradually raising the salinity of ponds in vain.

Research suggests applying caffeine – which is extremely toxic to frogs – or using electrocution could help, but these approaches aren't always safe for other rare Galápagos species.

Lacking answers to more of the basic questions about their lifestyle and impact, culling the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of eDNA techniques and genetic analysis will help her group make sense of the invasive species, funding for the research has been difficult to obtain.

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