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During her daily commute to the scientific station, biologist Miriam San José stoops near a shallow pond surrounded by dense vegetation and retrieves a small green audio device.

She had placed there through the night to capture the characteristic calls of the Scinax quinquefasciatus, recognized by local scientists as an non-native species with consequences that experts are starting to comprehend.

Despite abounding with unique animals – such as ancient giant tortoises, swimming lizards, and the famous birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had long remained devoid of amphibians.

During the 1990s, this shifted. Some tiny tree frogs made their way from continental the mainland to the archipelago, probably as hitchhikers on cargo ships.

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

The population is expanding so quickly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could locate only a single tagged frog occasionally, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says San José. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

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

For the researchers, their nightly vocalizations are useful in determining their presence in far-flung areas, using recorders like the one near the office.

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

"During the rainy period, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"Initially it was a surprise, observing the first frogs in the area," says Larrea Saltos, who started observing their large numbers about three years ago when one jumped on her hand as she was walking out of her house.

Environmental Consequences Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost 30 years, scientists still know very little about its effect on the archipelago's precariously balanced land and water environments.

On islands, it is very common for non-native species to prosper, as they have few of their enemies. The islands counts over sixteen hundred invasive types, many of which are significantly disrupting the safety of its native ones.

A 2020 research indicates the non-native frogs are voracious insect consumers, and might be disproportionately consuming uncommon bugs found only on the islands, or depleting the food sources of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their development process is also highly variable, with some tadpoles becoming frogs very quickly and others taking a long time: San José observed one which remained as a larva in her laboratory for six months.

"We really don't know this part," she says, concerned the larvae could be impacting the islands' clean water, a very limited resource in the islands.

Methods to curb the amphibians in the early 2000s were mostly ineffective. Conservation officers tried capturing large numbers by hand and gradually increasing the salinity of lagoons in without success.

Studies suggests spraying coffee – which is highly poisonous to amphibians – or using electrical methods could help, but these approaches aren't always secure for other rare Galápagos organisms.

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

Funding Challenges for Study

While she hopes the increasing use of eDNA techniques and genetic analysis will help her team understand of the invasive species, financial support for the research has been hard to come by.

"Everyone wants to give funding for protecting frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to manage."