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During her daily commute to the scientific station, scientist Miriam San José crouches near a small water body covered by thick plants and retrieves a small green sound device.

The device was left there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an invasive threat with consequences that scientists are starting to understand.

Despite abounding with unique animals – including ancient large turtles, marine lizards, and the well-known finches that inspired Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of Ecuador had historically been free of frogs and toads.

During the 1990s, this shifted. Some small amphibians made their way from mainland Ecuador to the archipelago, probably as stowaways on cargo ships.

Genetic studies indicate that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm foothold on several locations: multiple locations.

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

When the biologist marked amphibians and attempted to recapture them in the following 10 days, she could find just one tagged frog from time to time, indicating their numbers were enormous.

They estimated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

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

For the scientists, their nocturnal mating calls are useful in determining their presence in remote areas, using audio devices like the one outside San José's workplace.

But nearby agricultural workers say the sounds are so raucous they prevent sleep at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

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

Environmental Consequences Remains Unknown

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost 30 years, experts still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for non-native species to thrive, as they have none of their enemies. The islands has 1,645 invasive species, many of which are significantly disrupting the survival of its endemic ones.

A recent study suggests the invasive frogs are voracious bug consumers, and might be unevenly eating uncommon bugs 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 island frogs have exhibited some atypical traits, including living in brackish water, which is rare for frogs.

Their metamorphosis process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José observed one which remained as a tadpole in her laboratory for six months.

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

Techniques to curb the amphibians in the beginning of the century were mostly ineffective. Park rangers tried collecting significant quantities by hand and gradually increasing the salinity of lagoons in without success.

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

Lacking answers to more of the basic issues about their biology and impact, removing the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she expects the increasing use of eDNA methods and genetic examination will help her group understand of the invasive species, funding for the research has been difficult to obtain.

"Everyone wants to give support for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to control."