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On her regular commute to the research facility, biologist Miriam San José crouches near a shallow water body covered by thick plants and retrieves a compact plastic audio device.

The device was left there overnight to record the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive threat with consequences that scientists are starting to comprehend.

Although abounding with remarkable wildlife – such as centuries-old large turtles, swimming lizards, and the well-known finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had long remained free of frogs and toads.

In the late 1990s, this changed. Some small amphibians traveled from mainland the mainland to the archipelago, probably as stowaways on transport vessels.

Genetic research indicate that, over the years, there have been repeated unintentional arrivals to the archipelago, and the amphibians now have a strong presence on several locations: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to monitor, estimating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation Galápagos national park.

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

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I'm quite certain there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nocturnal mating calls are helpful in determining their presence in remote areas, using recorders like the one near the workplace.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

"During the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started observing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Environmental Consequences Remains Unclear

The noise isn't the primary problem, however. While the amphibians has been in the islands for almost 30 years, scientists still know very little about its impact on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very common for invasive organisms to thrive, as they have none of their natural predators. The Galápagos has over sixteen hundred introduced types, many of which are seriously disrupting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are voracious bug consumers, and might be unevenly consuming rare insects found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

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

Their development stage is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José witnessed one which remained as a tadpole in her laboratory for half a year.

"We really don't know this part," she says, concerned the tadpoles could be affecting the islands' freshwater, a very scarce commodity in the islands.

Techniques to curb the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried capturing significant quantities by hand and slowly increasing the salinity of lagoons in vain.

Studies suggests applying coffee – which is extremely poisonous to frogs – or using electrocution could help, but these approaches aren't always secure for other uncommon island species.

Without answers to more of the fundamental questions about their lifestyle and effect, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and DNA analysis will help her team understand of the invader, financial support for the project has been hard to obtain.

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