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On her regular commute to the research facility, biologist Miriam San José crouches near a small water body surrounded by thick vegetation and collects a compact green audio device.

She had placed there through the night to capture the distinctive croaks of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with effects that experts are starting to understand.

Although teeming with remarkable wildlife – including ancient large turtles, swimming lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had historically been free of amphibians.

During the 1990s, this shifted. Several small amphibians made their way from mainland the mainland to the islands, likely as stowaways on transport vessels.

DNA studies indicate that, over the years, there have been multiple accidental introductions to the archipelago, and the frogs now have a firm presence on several islands: Isabela and Santa Cruz.

The numbers is expanding so rapidly that researchers have been struggling to keep track, calculating populations in the millions on every island, across developed and farming areas, but also in the protected natural reserve.

When the biologist tagged frogs and attempted to recapture them in the subsequent 10 days, she could find only a single marked frog occasionally, suggesting their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states the researcher. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The frogs' proliferation is evident from the sound disruption they cause. "The amount of frogs and the sound – it's really insane," comments San José.

For the scientists, their nocturnal vocalizations are useful in estimating their existence in far-flung areas, using recorders like the one near the workplace.

But nearby agricultural workers say the calls are so loud they prevent sleep at night.

"In the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

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

Environmental Consequences Stays Unclear

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

On archipelagos, it is very typical for non-native species to prosper, as they have few of their enemies. The islands has over sixteen hundred introduced species, many of which are seriously disrupting the safety of its native ones.

A 2020 study suggests the non-native frogs are hungry insect eaters, and might be unevenly eating rare bugs found exclusively on the archipelago, or depleting the food sources of the region's uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

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

"We truly don't know this part," she says, concerned the larvae could be affecting the region's freshwater, a very limited commodity in the islands.

Methods to control the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried collecting significant quantities by manual methods and gradually raising the salinity of ponds in vain.

Studies suggests applying caffeine – which is extremely poisonous to amphibians – or using electrical methods could help, but these methods aren't always safe for other uncommon island organisms.

Without answers to more of the fundamental issues about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA techniques and DNA examination will help her team make sense of the invasive species, funding for the project has been hard to obtain.

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