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During her daily commute to the research facility, scientist Miriam San José stoops near a shallow water body surrounded by dense vegetation and retrieves a compact plastic audio recorder.

The device was left 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.

Despite teeming with unique wildlife – including ancient large turtles, marine iguanas, and the well-known finches that sparked Darwin's evolutionary theory – the island chain near the shoreline of Ecuador had long remained free of amphibians.

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

DNA research indicate that, through time, there have been multiple accidental arrivals to the archipelago, and the amphibians now have a firm presence on two locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been struggling to monitor, calculating numbers in the millions on every island, across urban and farming areas, but also in the conservation Galápagos national park.

When the biologist marked amphibians and attempted to find them in the subsequent week and a half, she could locate just one tagged frog from time to time, indicating their populations were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

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

For the researchers, their nightly vocalizations are helpful in determining their existence in remote areas, using audio devices like the one near the office.

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

"In the rainy period, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"At first it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for non-native organisms to prosper, as they have few of their natural predators. The islands has over sixteen hundred introduced types, many of which are significantly disrupting the survival of its native ones.

A 2020 study suggests the non-native frogs are hungry bug eaters, and might be disproportionately consuming rare bugs found only on the islands, or depleting the nutrition of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The island frogs have exhibited some atypical traits, including living in slightly salty water, which is uncommon for amphibians.

Their metamorphosis process is also highly variable, with some tadpoles turning into frogs very quickly and others taking a long time: the researcher observed one which remained as a larva in her laboratory for half a year.

"We really don't know this aspect," she says, worried the larvae could be impacting the region's clean water, a very limited commodity in the islands.

Techniques to control the amphibians in the beginning of the century were largely ineffective. Park rangers tried collecting large numbers by hand and slowly increasing the salinity of lagoons in without success.

Research suggests spraying coffee – which is highly toxic to amphibians – or using electrocution could help, but these approaches aren't always safe for other rare island species.

Without solutions to more of the basic issues about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and DNA examination will assist her group make sense of the invasive species, funding for the research has been hard to obtain.

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