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On her daily walk to the scientific station, biologist the researcher crouches near a small water body covered by dense plants and collects a compact plastic sound recorder.

The device was left there overnight to record the characteristic calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with consequences that scientists are just beginning to understand.

Despite teeming with remarkable wildlife – including ancient giant tortoises, swimming lizards, and the well-known finches that sparked Darwin's evolutionary theory – the Galápagos archipelago near the coast of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this changed. Several small amphibians traveled from mainland the mainland to the archipelago, likely as hitchhikers on cargo ships.

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

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

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could find only a single tagged frog from time to time, suggesting their populations were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' abundance is evident from the sound chaos they create. "The number of frogs and the sound – it's really incredible," says San José.

For the researchers, their nightly vocalizations are helpful in determining their presence in remote 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.

"During the wet season, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a shock, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

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

On archipelagos, it is very common for non-native species to thrive, as they have none of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are seriously disrupting the safety of its native ones.

A 2020 research indicates the invasive amphibians are hungry bug eaters, and might be unevenly eating uncommon insects found only on the archipelago, or depleting the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island frogs have shown some atypical traits, including living in brackish water, which is rare for frogs.

Their metamorphosis process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for half a year.

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

Techniques to control the amphibians in the early 2000s were mostly ineffective. Park rangers tried capturing large numbers by manual methods and slowly raising the salt content of ponds in without success.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrical methods could assist, but these approaches aren't always safe for other rare island organisms.

Without solutions to more of the basic issues about their biology and impact, culling the amphibians might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA methods and genetic analysis will assist her group understand of the invasive species, financial support for the project has been difficult to come by.

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