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During her daily walk to the scientific station, scientist the researcher crouches near a small water body covered by thick vegetation and collects a small green sound device.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos researchers as an non-native threat with effects that scientists are just beginning to understand.

Despite abounding with unique wildlife – such as centuries-old giant tortoises, marine iguanas, and the well-known birds that sparked Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of Ecuador had historically been devoid of amphibians.

In the late 1990s, this changed. Several tiny amphibians made their way 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 archipelago, and the amphibians now have a strong presence on two locations: multiple locations.

The population is growing so rapidly that researchers have been finding it difficult to keep track, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José tagged amphibians and attempted to recapture them in the following 10 days, she could locate only a single tagged frog from time to time, suggesting their numbers were massive.

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," states San José. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the sound chaos they create. "The number of frogs and the sound – it's really insane," comments San José.

For the scientists, their nocturnal mating calls are helpful in determining their presence in far-flung areas, using recorders like the one near the workplace.

But local agricultural workers say the sounds are so loud they keep them up at night.

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

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

Environmental Consequences Stays Unknown

The noise isn't the primary problem, though. While the amphibians has been in the islands for almost 30 years, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive organisms to thrive, as they have none of their enemies. The islands counts 1,645 invasive species, many of which are seriously affecting the survival of its endemic ones.

A 2020 study suggests the non-native frogs are voracious bug eaters, and might be unevenly consuming uncommon bugs found only on the islands, or reducing the nutrition of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some unusual characteristics, including surviving in slightly salty water, which is rare for amphibians.

Their metamorphosis process is also extremely inconsistent, with some larvae turning into frogs very quickly and others taking a extended period: San José observed one which remained as a tadpole in her lab for six months.

"We truly don't know this aspect," she says, worried the larvae could be impacting the islands' freshwater, a very limited resource in Galápagos.

Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried collecting large numbers by manual methods and gradually raising the salt content of ponds in vain.

Research indicates spraying coffee – which is extremely poisonous to frogs – or using electrocution could assist, but these methods aren't necessarily secure for other uncommon island species.

Without solutions to more of the basic questions about their biology and effect, culling the amphibians might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she hopes the increasing use of environmental DNA techniques and genetic examination will help her team understand of the invader, funding for the research has been hard to obtain.

"Everyone wants to give support for protecting frogs," says the researcher. "But it's harder to find funding for an invasive frog that you might want to control."