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During her daily walk to the research facility, biologist Miriam San José crouches near a small pond covered by dense vegetation and retrieves a small green audio recorder.

She had placed there overnight to record the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with effects that experts are just beginning to comprehend.

Despite teeming with remarkable wildlife – such as ancient giant tortoises, swimming lizards, and the well-known finches that sparked Charles Darwin's theory of evolution – the island chain off the coast of South America had long remained devoid of amphibians.

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

DNA studies indicate that, over the years, there have been repeated accidental introductions to the islands, and the amphibians now have a firm foothold on several locations: multiple locations.

The population is growing so quickly that scientists have been finding it difficult to monitor, estimating numbers in the millions on every island, across urban and agricultural areas, but also in the conservation natural reserve.

When the biologist tagged amphibians and attempted to recapture them in the subsequent 10 days, she could locate only a single marked frog occasionally, indicating their numbers were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the acoustic disruption they cause. "The number of frogs and the sound – it's truly incredible," comments the scientist.

For the scientists, their nightly mating calls are useful in estimating their presence in remote areas, using audio devices like the one near San José's office.

But nearby agricultural workers say the sounds are so loud 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.

"Initially it was a surprise, seeing the first 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 Stays Unclear

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

On archipelagos, it is very common for non-native species to thrive, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced types, many of which are significantly affecting the safety of its native ones.

A 2020 study indicates the invasive amphibians are voracious bug eaters, and might be unevenly consuming rare insects found only on the archipelago, or depleting the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

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

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

Techniques to curb the amphibians in the beginning of the century were largely ineffective. Conservation officers tried capturing large numbers by hand and slowly raising the salt content of ponds in without success.

Studies suggests spraying caffeine – which is highly toxic to frogs – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon island organisms.

Without answers to more of the fundamental questions about their lifestyle and effect, removing the frogs might not even be the right way to proceed, says San José.

Financial Obstacles for Study

While she expects the increasing use of environmental DNA techniques and DNA analysis will assist her team make sense of the invader, funding for the project has been difficult to come by.

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