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On her daily walk to the scientific station, scientist Miriam San José stoops near a shallow pond covered by dense plants and collects a small green sound recorder.

The device was left there through the night to record the distinctive calls of the Scinax quinquefasciatus, known by local researchers as an non-native species with consequences that experts are just beginning to comprehend.

Although abounding with remarkable animals – such as centuries-old giant tortoises, marine iguanas, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this changed. Several small tree frogs made their way from mainland the mainland to the islands, likely as stowaways on cargo ships.

Genetic studies suggest that, over the years, there have been multiple unintentional introductions to the archipelago, and the frogs now have a strong foothold on several islands: multiple locations.

The population is growing so rapidly that researchers have been finding it difficult to monitor, calculating numbers in the millions on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When the biologist marked amphibians and attempted to find them in the subsequent week and a half, she could find just one tagged frog occasionally, suggesting their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very low," states the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

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

For the scientists, their nightly mating calls are helpful in determining their existence in far-flung areas, using audio devices like the one outside the office.

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

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

"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about several years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unknown

The sound isn't the primary problem, however. While the amphibians has been in the islands for almost three decades, experts still know limited information about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for non-native organisms to prosper, as they have few of their natural predators. The islands counts over sixteen hundred introduced species, many of which are significantly affecting the survival of its native ones.

A 2020 study suggests the invasive amphibians are voracious bug eaters, and might be unevenly consuming rare bugs found exclusively on the islands, or reducing the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The Galápagos frogs have shown some unusual characteristics, including surviving in slightly salty water, which is rare for frogs.

Their development stage is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a tadpole in her laboratory for half a year.

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

Techniques to curb the amphibians in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and gradually increasing the salt content of ponds in vain.

Research suggests applying caffeine – which is highly toxic to amphibians – or using electrical methods could help, but these approaches aren't always safe for other uncommon Galápagos species.

Lacking solutions to more of the fundamental questions about their lifestyle and effect, removing the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she hopes the growing use of eDNA methods and genetic examination will help her team understand of the invasive species, financial support for the research has been hard to come by.

"Everyone wants to give funding for preserving frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to manage."