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On her daily commute to the scientific station, scientist the researcher crouches near a small water body surrounded by thick plants and collects a small green audio recorder.

She had placed there through the night to record the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native species with consequences that experts are just beginning to comprehend.

Although teeming with remarkable animals – including ancient large turtles, swimming lizards, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained free of frogs and toads.

During the 1990s, this changed. Several small amphibians traveled from continental Ecuador to the islands, likely as stowaways on transport vessels.

DNA studies indicate that, over the years, there have been multiple accidental arrivals to the islands, and the frogs now have a strong foothold on several locations: Isabela and Santa Cruz.

The population is expanding so quickly that researchers have been struggling to monitor, estimating numbers in the millions on every island, across developed and farming areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the subsequent week and a half, she could locate only a single tagged frog from time to time, indicating their numbers were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the acoustic disruption they create. "The amount of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nightly mating calls are useful in estimating their existence in far-flung areas, using audio devices like the one outside San José's office.

But nearby farmers say the sounds are so loud they prevent sleep at night.

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

"At first it was a shock, seeing the first frogs in the area," says the farmer, who started observing their abundance about several years ago when one leaped on her palm as she was stepping out of her front door.

Ecological Impact Stays Unknown

The sound isn't the primary problem, though. While the amphibians has been in the Galápagos for nearly 30 years, experts still know very little about its impact on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive organisms to thrive, as they have few of their natural predators. The Galápagos has 1,645 invasive types, many of which are seriously disrupting the safety of its endemic ones.

A recent study indicates the invasive frogs are hungry bug eaters, and might be disproportionately consuming rare insects found only on the islands, or reducing the nutrition of the region's uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

The Galápagos amphibians have shown some unusual characteristics, including living in slightly salty water, which is uncommon for frogs.

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

"We really don't know this part," she says, worried the tadpoles could be affecting the region's freshwater, a very limited commodity in Galápagos.

Techniques to control the amphibians in the beginning of the century were largely ineffective. Park rangers tried capturing significant quantities by manual methods and slowly increasing the salt content of lagoons in without success.

Research indicates spraying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these methods aren't always safe for other rare Galápagos organisms.

Lacking solutions to more of the basic questions about their biology and effect, culling the frogs might not even be the right way to proceed, says San José.

Funding Challenges for Research

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

"Everyone wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an introduced frog that you might want to manage."