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During her regular commute to the research facility, scientist the researcher crouches near a small water body surrounded by dense plants and collects a small plastic audio recorder.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, known by local researchers as an non-native species with consequences that scientists are starting to comprehend.

Although teeming with remarkable animals – including centuries-old large turtles, swimming lizards, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of Ecuador had long remained free of amphibians.

In the late 1990s, this changed. Some small tree frogs traveled from mainland Ecuador to the islands, likely as hitchhikers on cargo ships.

DNA research suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the amphibians now have a firm foothold on two islands: Isabela and Santa Cruz.

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

When San José marked amphibians and attempted to recapture them in the following week and a half, she could find just one marked frog from time to time, suggesting their populations were enormous.

They calculated six thousand frogs in a single pond. "Our estimates are still very conservative," states the researcher. "I'm quite certain there are even more."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic chaos they cause. "The number of frogs and the sound – it's really incredible," says the scientist.

For the researchers, their nocturnal mating calls are useful in determining their presence in remote areas, using audio devices like the one near the office.

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

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

"Initially it was a surprise, observing the first frogs in the area," says the farmer, who started observing their large numbers about three years ago when one jumped on her palm as she was walking out of her front door.

Ecological Impact Stays Unclear

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

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

A 2020 research indicates the non-native frogs are hungry bug consumers, and might be unevenly consuming uncommon bugs found exclusively on the islands, or reducing the nutrition of the islands' rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher observed one which stayed as a tadpole in her lab for half a year.

"We really don't know this part," she says, worried the larvae could be impacting the islands' clean water, a very scarce resource in Galápagos.

Techniques to control the amphibians in the early 2000s were largely ineffective. Park rangers tried collecting large numbers by manual methods and gradually raising the salinity of ponds in without success.

Research suggests spraying caffeine – which is extremely poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily safe for other rare Galápagos organisms.

Without answers to more of the basic questions about their lifestyle and impact, culling the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Research

While she hopes the growing use of environmental DNA methods and genetic analysis will assist her group make sense of the invader, funding for the research has been hard to obtain.

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