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During her regular walk to the scientific station, scientist the researcher crouches near a small water body covered by thick plants and retrieves a small green audio device.

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

Despite teeming with remarkable animals – including ancient giant tortoises, marine lizards, and the well-known finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had long remained free of frogs and toads.

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

DNA research suggest that, through time, there have been repeated unintentional introductions to the archipelago, and the frogs now have a strong foothold on several islands: multiple locations.

The numbers is expanding so rapidly that scientists have been struggling to keep track, calculating populations in the millions on each island, across developed and farming areas, but also in the protected natural reserve.

When San José marked frogs and attempted to find them in the following 10 days, she could locate just one marked frog occasionally, indicating their numbers were massive.

They calculated 6,000 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 frogs' proliferation is evident from the sound disruption they create. "The amount of frogs and the sound – it's truly insane," comments San José.

For the researchers, their nightly mating calls are useful in determining their presence in remote areas, using audio devices like the one outside the workplace.

But nearby farmers say the calls are so raucous they keep them up at night.

"During the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

"At first it was a surprise, seeing the first frogs in the area," says Larrea Saltos, who started noticing their abundance about three years ago when one leaped on her palm as she was walking out of her front door.

Environmental Consequences Stays Unclear

The sound isn't the primary problem, however. While the amphibians has been in the Galápagos for almost 30 years, experts still know very little about its effect 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 few of their enemies. The Galápagos counts 1,645 invasive species, many of which are significantly affecting the safety of its native ones.

A recent research suggests the non-native frogs are hungry bug eaters, and might be unevenly consuming uncommon insects found exclusively on the islands, or depleting the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos amphibians 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 becoming frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a larva in her laboratory for half a year.

"We truly don't know this part," she says, concerned the tadpoles could be affecting the region's clean water, a very scarce commodity in the islands.

Methods to control the amphibians in the early 2000s were largely ineffective. Park rangers tried capturing significant quantities by manual methods and gradually raising the salinity of lagoons in without success.

Research suggests applying coffee – which is extremely poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon Galápagos organisms.

Without solutions to more of the fundamental issues about their lifestyle and impact, culling the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she hopes the growing use of eDNA methods and genetic analysis will assist her team understand of the invader, funding for the research has been difficult to obtain.

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