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During her regular commute to the scientific station, biologist the researcher crouches near a shallow water body covered by dense vegetation and collects a small green sound device.

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

Although abounding with unique wildlife – including ancient giant tortoises, swimming iguanas, and the famous birds that sparked Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this shifted. Several tiny tree frogs traveled from continental the mainland to the archipelago, likely as stowaways on cargo ships.

DNA studies suggest that, over the years, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a firm foothold on several islands: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been struggling to keep track, calculating numbers in the millions on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged amphibians and attempted to find them in the subsequent week and a half, she could locate only a single tagged frog occasionally, indicating their numbers were massive.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says the researcher. "I'm pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

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

For the scientists, their nightly vocalizations are useful in estimating their presence in far-flung areas, using audio devices like the one near the workplace.

But local 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 extremely loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Remains Unknown

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

On archipelagos, it is very common for invasive species to prosper, as they have few of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study suggests the non-native frogs are voracious bug eaters, and might be disproportionately eating uncommon insects found only on the islands, or reducing the nutrition of the islands' rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island amphibians have exhibited some unusual characteristics, including surviving in brackish water, which is rare for amphibians.

Their metamorphosis process is also highly variable, with some tadpoles turning into frogs very rapidly and others taking a long time: San José witnessed one which remained as a tadpole in her laboratory for half a year.

"We truly don't know this aspect," she says, worried the tadpoles could be affecting the region's freshwater, a very scarce resource in the islands.

Techniques to control the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting large numbers by manual methods and slowly raising the salinity of ponds 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 secure for other rare Galápagos organisms.

Without solutions to more of the fundamental issues about their biology and impact, removing the frogs might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she hopes the increasing use of eDNA methods and DNA analysis will help her group make sense of the invader, financial support for the research has been difficult to come by.

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