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During her regular commute to the research facility, scientist Miriam San José stoops near a shallow pond surrounded by thick plants and retrieves a small green audio device.

The device was left there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by local researchers as an invasive threat with consequences that experts are starting to understand.

Although teeming with unique animals – including centuries-old large turtles, marine lizards, and the well-known finches that sparked Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of South America had historically been free of frogs and toads.

During the 1990s, this changed. Several small amphibians made their way from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

Genetic studies indicate that, over the years, there have been multiple unintentional arrivals to the islands, and the frogs now have a strong presence on several islands: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to monitor, calculating populations in the millions on every island, across developed and agricultural areas, but also in the protected Galápagos national park.

When the biologist tagged frogs and attempted to find them in the subsequent week and a half, she could locate only a single tagged frog from time to time, suggesting their numbers were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," says San José. "I am quite certain there are even more."

Acoustic Chaos and Rising Worries

The frogs' proliferation is clear from the acoustic disruption they cause. "The amount of frogs and the noise – it's really incredible," comments the scientist.

For the scientists, their nightly mating calls are helpful in estimating their presence in remote areas, using audio devices like the one near the workplace.

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

"In the wet season, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

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

Environmental Consequences Remains Unknown

The sound isn't the fundamental problem, however. While the species has been in the islands for almost three decades, experts still know limited information about its effect on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very typical for non-native species to prosper, as they have none of their natural predators. The Galápagos counts over sixteen hundred introduced species, many of which are significantly affecting the safety of its native ones.

A recent research indicates the invasive frogs are voracious insect eaters, and might be disproportionately consuming uncommon insects found exclusively on the islands, or depleting the nutrition of the region's rare birds, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their development process is also highly inconsistent, with some larvae becoming frogs very rapidly and others taking a extended period: San José witnessed one which remained as a tadpole in her laboratory for six months.

"We really don't know this aspect," she says, worried the tadpoles could be affecting the region's clean water, a very scarce resource in the islands.

Techniques to control the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried capturing large numbers by manual methods and slowly increasing the salt content of lagoons in without success.

Studies suggests applying caffeine – which is extremely poisonous to amphibians – or using electrical methods could assist, but these methods aren't always secure for other rare island organisms.

Without answers to more of the basic issues about their lifestyle and effect, removing the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and genetic analysis will help her group understand of the invader, financial support for the research has been hard to come by.

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