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On her daily walk to the research facility, biologist Miriam San José crouches near a shallow pond surrounded by thick vegetation and retrieves a compact green audio device.

She had placed there overnight to record the characteristic calls of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with effects that experts are just beginning to comprehend.

Although abounding with unique wildlife – including ancient large turtles, marine iguanas, and the well-known birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had long remained free of frogs and toads.

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

DNA research indicate that, over the years, there have been repeated unintentional arrivals to the islands, and the frogs now have a strong foothold on two locations: Isabela and Santa Cruz.

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

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

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is clear from the sound chaos they cause. "The amount of frogs and the noise – it's really incredible," comments San José.

For the scientists, their nocturnal vocalizations are helpful in determining their presence in far-flung areas, using audio devices like the one outside the office.

But nearby farmers say the sounds are so loud they prevent sleep at night.

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

"Initially it was a surprise, seeing the first frogs in the region," says the farmer, who started observing their large numbers about several years ago when one leaped on her palm as she was stepping out of her front door.

Environmental Consequences Stays Unclear

The sound isn't the fundamental problem, however. While the amphibians has been in the islands for nearly 30 years, experts still know limited information about its impact on the islands' delicately balanced land and water ecosystems.

On archipelagos, it is very common for invasive organisms to thrive, as they have none of their enemies. The islands has over sixteen hundred invasive types, many of which are significantly disrupting the survival of its endemic ones.

A 2020 research suggests the invasive frogs are voracious insect eaters, and might be disproportionately consuming uncommon bugs found only on the islands, or reducing the nutrition of the islands' rare birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some atypical traits, including surviving in slightly salty water, which is rare for amphibians.

Their metamorphosis process is also highly variable, with some tadpoles turning into 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 tadpoles could be affecting the region's freshwater, a very scarce resource in the islands.

Techniques to curb the frogs in the beginning of the century were mostly ineffective. Park rangers tried collecting large numbers by hand and slowly increasing the salt content of lagoons in without success.

Studies indicates applying caffeine – which is extremely poisonous to frogs – or using electrical methods could assist, but these methods aren't always safe for other rare island organisms.

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

Financial Obstacles for Research

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

"Everybody wants to give funding for preserving frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to control."