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On her daily walk to the research facility, scientist the researcher crouches near a shallow pond covered by thick vegetation and collects a compact green sound device.

She had placed there through the night to record the characteristic calls of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that experts are starting to understand.

Although teeming with remarkable wildlife – such as centuries-old giant tortoises, marine lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had long remained devoid of amphibians.

During the 1990s, this shifted. Some tiny tree frogs made their way from continental Ecuador to the islands, probably as stowaways on transport vessels.

DNA studies suggest that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong foothold on several islands: Isabela and Santa Cruz.

The numbers is growing so rapidly that researchers have been finding it difficult to monitor, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation natural reserve.

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

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," states the researcher. "I am quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is evident from the sound chaos they create. "The amount of frogs and the sound – it's really incredible," says the scientist.

For the scientists, their nocturnal vocalizations are useful in estimating their existence in far-flung areas, using recorders like the one near San José's workplace.

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

"In the rainy period, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, however. While the species has been in the Galápagos for almost three decades, scientists still know limited information about its impact on the islands' precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very common for invasive species to thrive, as they have none of their natural predators. The Galápagos counts over sixteen hundred invasive species, many of which are significantly affecting the survival of its endemic ones.

A 2020 study indicates the non-native frogs are hungry insect eaters, and might be disproportionately eating rare bugs found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which stayed as a larva in her lab for half a year.

"We truly don't know this part," she says, concerned the larvae could be impacting the islands' freshwater, a very scarce commodity in Galápagos.

Techniques to control the frogs in the beginning of the century were mostly ineffective. Park rangers tried capturing significant quantities by manual methods and gradually increasing the salinity of ponds in vain.

Research indicates applying coffee – which is extremely toxic to frogs – or using electrocution could help, but these approaches aren't always safe for other uncommon Galápagos species.

Lacking answers to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the right way to advance, says San José.

Financial Obstacles for Study

While she hopes the increasing use of eDNA techniques and genetic analysis will assist her team understand of the invasive species, financial support for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to control."