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On her regular commute to the scientific station, scientist Miriam San José stoops near a small water body covered by thick plants and retrieves a compact green audio recorder.

The device was left there overnight to record the distinctive croaks of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native species with effects that experts are just beginning to comprehend.

Despite teeming with unique animals – including ancient giant tortoises, marine lizards, and the famous birds that inspired Darwin's theory of evolution – the island chain off the coast of South America had long remained free of amphibians.

In the late 1990s, this changed. Several tiny amphibians made their way from mainland Ecuador to the archipelago, probably as stowaways on cargo ships.

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

The population is expanding so rapidly that scientists have been struggling to keep track, estimating numbers in the millions on every 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 following 10 days, she could locate only a single tagged frog from time to time, indicating their numbers were enormous.

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

Deafening Noise and Growing Concerns

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

For the scientists, their nightly mating calls are helpful in estimating their existence in far-flung areas, using recorders like the one outside San José's workplace.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

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

"At first it was a shock, seeing the initial frogs in the area," says Larrea Saltos, who started noticing their abundance about three years ago when one jumped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unclear

The noise isn't the primary problem, though. While the amphibians has been in the islands for nearly three decades, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive species to thrive, as they have few of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are significantly affecting the survival of its endemic ones.

A 2020 study indicates the invasive frogs are hungry insect eaters, and might be unevenly consuming uncommon insects found only on the islands, or reducing the food sources of the region's rare avian species, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some atypical traits, including surviving in brackish water, which is uncommon for amphibians.

Their development stage is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which stayed as a tadpole in her lab for six months.

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

Techniques to control the amphibians in the beginning of the century were largely ineffective. Conservation officers tried collecting large numbers by manual methods and gradually increasing the salt content of ponds in without success.

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

Lacking solutions to more of the fundamental questions about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she expects the increasing use of environmental DNA methods and DNA analysis will help her group understand of the invasive species, funding for the project has been difficult to come by.

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