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During her regular walk to the scientific station, scientist the researcher stoops near a shallow water body surrounded by dense vegetation and retrieves a small plastic audio device.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native species with consequences that experts are just beginning to comprehend.

Although teeming with remarkable wildlife – including ancient giant tortoises, swimming lizards, and the famous finches that inspired Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had historically been devoid of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA studies indicate that, through time, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm foothold on several islands: multiple locations.

The population is growing so quickly 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 Galápagos national park.

When the biologist tagged amphibians and attempted to recapture them in the subsequent week and a half, she could find only a single tagged frog occasionally, indicating their populations were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," states the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

The frogs' proliferation is clear from the acoustic disruption they cause. "The number of frogs and the noise – it's really insane," comments San José.

For the researchers, their nightly vocalizations are useful in estimating their existence in far-flung areas, using audio devices like the one near San José's office.

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

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

"At first it was a surprise, observing the initial frogs in the region," says the farmer, who started observing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the islands for nearly three decades, scientists still know limited information about its impact on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very typical for invasive species to prosper, as they have none of their natural predators. The islands has over sixteen hundred invasive types, many of which are seriously affecting the safety of its endemic ones.

A 2020 study suggests the invasive amphibians are hungry bug eaters, and might be disproportionately eating uncommon insects found only on the islands, or reducing the food sources of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

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

Their development stage is also highly variable, with some larvae becoming frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a larva in her lab for half a year.

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

Methods to control the frogs in the early 2000s were mostly unsuccessful. Park rangers tried capturing significant quantities by hand and slowly raising the salt content of ponds in without success.

Studies suggests applying coffee – which is highly poisonous to frogs – or using electrocution could assist, but these approaches aren't always safe for other rare Galápagos species.

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

Financial Obstacles for Study

While she hopes the increasing use of environmental DNA methods and DNA analysis will assist her group understand of the invasive species, funding for the research has been hard to obtain.

"Everybody wants to give support 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."