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During her daily walk to the scientific station, biologist the researcher crouches near a shallow pond covered by dense plants and collects a compact plastic sound recorder.

She had placed there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, known by Galápagos researchers as an invasive species with consequences that scientists are just beginning to understand.

Although abounding with unique wildlife – including centuries-old large turtles, marine iguanas, and the famous birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of Ecuador had long remained free of frogs and toads.

In the late 1990s, this shifted. Several tiny tree frogs traveled from mainland Ecuador to the archipelago, probably as hitchhikers on cargo ships.

Genetic studies suggest that, through time, there have been multiple accidental arrivals to the islands, and the frogs now have a firm presence on two islands: multiple locations.

The population is growing so rapidly that researchers have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to find them in the subsequent 10 days, she could locate only a single marked frog from time to time, suggesting their populations were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," says San José. "I am quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

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

For the scientists, their nocturnal vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one near San José's office.

But local farmers say the calls are so raucous they prevent sleep at night.

"During the rainy period, 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 area," says the farmer, who started observing their abundance about several years ago when one leaped on her hand as she was stepping out of her house.

Environmental Consequences Remains Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive species to prosper, as they have none of their enemies. The islands has 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A 2020 research indicates the invasive frogs are voracious bug consumers, and might be unevenly consuming uncommon insects found exclusively on the islands, or reducing the nutrition of the region's uncommon birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their metamorphosis process is also extremely variable, with some tadpoles turning into frogs very rapidly and others taking a long time: the researcher witnessed one which remained as a tadpole in her laboratory for six months.

"We truly don't know this aspect," she says, concerned the larvae could be affecting the islands' freshwater, a very scarce resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting large numbers by manual methods and gradually raising the salinity of ponds in without success.

Studies suggests spraying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily safe for other rare island species.

Lacking answers to more of the basic issues about their biology and effect, culling the frogs might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and DNA examination will help her group make sense of the invader, funding for the project has been hard to come by.

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