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On her regular walk to the scientific station, biologist the researcher crouches near a small water body surrounded by thick plants and retrieves a small green sound device.

The device was left there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with consequences that scientists are starting to understand.

Although teeming with unique animals – including centuries-old giant tortoises, swimming lizards, and the famous birds that inspired Darwin's evolutionary theory – the island chain near the shoreline of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this changed. Several small amphibians traveled from mainland Ecuador to the archipelago, probably as hitchhikers on transport vessels.

Genetic research indicate that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong foothold on two islands: multiple locations.

The numbers is growing so quickly that scientists have been struggling to keep track, calculating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the conservation natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent 10 days, she could locate only a single tagged frog from time to time, suggesting their populations were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very low," states the researcher. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the sound disruption they cause. "The number of frogs and the sound – it's truly insane," says San José.

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

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

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

"At first it was a surprise, seeing the initial frogs in the region," says the farmer, who started observing their large numbers about three years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Stays Unknown

The sound isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, scientists still know very little about its effect on the archipelago's precariously balanced land and water ecosystems.

On islands, it is very typical for non-native species to prosper, as they have none of their enemies. The Galápagos has 1,645 introduced types, many of which are significantly disrupting the safety of its endemic ones.

A recent research indicates the invasive amphibians are voracious bug eaters, and might be disproportionately eating rare insects found only on the archipelago, or reducing the nutrition of the region's rare avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

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

Their development stage is also extremely variable, with some tadpoles turning into frogs very quickly and others taking a long time: the researcher observed one which stayed as a tadpole in her laboratory for six months.

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

Techniques to control the frogs in the beginning of the century were mostly ineffective. Park rangers tried collecting large numbers by hand and slowly increasing the salinity of ponds in without success.

Research indicates spraying coffee – which is extremely toxic to frogs – or using electrocution could assist, but these approaches aren't always secure for other uncommon island organisms.

Lacking solutions to more of the fundamental issues about their lifestyle and impact, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of eDNA techniques and genetic examination will assist her team make sense of the invasive species, financial support for the project has been difficult to obtain.

"Everybody wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to manage."