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During her daily walk to the scientific station, scientist Miriam San José stoops near a small water body covered by thick plants and collects a compact plastic audio device.

The device was left there overnight to record the distinctive croaks of the Scinax quinquefasciatus, known by local scientists as an invasive species with consequences that scientists are just beginning to comprehend.

Although teeming with remarkable animals – such as ancient large turtles, marine iguanas, and the well-known birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had historically been free of amphibians.

In the late 1990s, this shifted. Some small amphibians made their way from continental Ecuador to the islands, probably as stowaways on cargo ships.

Genetic studies indicate that, through time, there have been multiple unintentional arrivals to the islands, and the frogs now have a firm foothold on two locations: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been finding it difficult to keep track, estimating populations in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to find them in the following 10 days, she could find only a single marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very low," states the researcher. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the sound disruption they create. "The number of frogs and the sound – it's truly incredible," says the scientist.

For the researchers, their nocturnal vocalizations are helpful in determining their presence in remote areas, using audio devices like the one outside the office.

But nearby farmers say the calls are so loud they keep them up at night.

"In the rainy period, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Remains Unclear

The sound isn't the primary problem, however. While the species has been in the Galápagos for nearly 30 years, scientists still know very little about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very typical for invasive species to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are significantly disrupting the safety of its native ones.

A recent research suggests the invasive amphibians are hungry bug eaters, and might be disproportionately consuming rare bugs found only on the islands, or reducing the food sources of the islands' rare avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some atypical traits, including surviving in slightly salty water, which is uncommon for amphibians.

Their development stage is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a extended period: the researcher witnessed one which stayed as a tadpole in her laboratory for six months.

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

Techniques to curb the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried capturing large numbers by manual methods and slowly raising the salt content of ponds in vain.

Studies suggests spraying coffee – which is highly toxic to frogs – or using electrocution could assist, but these methods aren't necessarily secure for other uncommon Galápagos species.

Without solutions to more of the fundamental questions about their biology and impact, culling the frogs might not even be the right way to proceed, says San José.

Funding Challenges for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will assist her team understand of the invader, funding for the research has been hard to come by.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."