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On her daily walk to the scientific station, biologist Miriam San José stoops near a small pond covered by dense vegetation and collects a small green audio recorder.

The device was left there overnight to capture the characteristic calls of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive threat with consequences that experts are just beginning to comprehend.

Despite teeming with unique wildlife – such as ancient giant tortoises, swimming iguanas, and the well-known birds that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of Ecuador had long remained devoid of amphibians.

During the 1990s, this shifted. Several small tree frogs traveled from mainland Ecuador to the islands, likely as stowaways on cargo ships.

Genetic research suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a firm presence on two locations: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the protected Galápagos national park.

When the biologist marked amphibians and attempted to find them in the following 10 days, she could find only a single tagged frog occasionally, suggesting their numbers were enormous.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' proliferation is clear from the acoustic chaos they create. "The amount of frogs and the sound – it's truly insane," comments San José.

For the scientists, their nocturnal vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one near San José's office.

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

"During the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from the island.

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started noticing their large numbers about several years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Remains Unclear

The sound isn't the primary problem, however. While the amphibians has been in the islands for nearly 30 years, experts still know limited information about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for invasive organisms to thrive, as they have few of their natural predators. The islands has 1,645 introduced species, many of which are significantly affecting the safety of its native ones.

A recent study suggests the invasive amphibians are voracious bug consumers, and might be disproportionately eating rare bugs found only on the islands, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Management Difficulties

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

Their development stage is also extremely variable, with some larvae becoming frogs very rapidly and others taking a long time: San José witnessed one which stayed as a larva in her lab for six months.

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

Methods to control the amphibians in the early 2000s were mostly ineffective. Park rangers tried capturing large numbers by hand and slowly increasing the salinity of ponds in vain.

Research suggests spraying caffeine – which is extremely poisonous to frogs – or using electrical methods could assist, but these methods aren't always secure for other uncommon Galápagos organisms.

Without answers to more of the fundamental issues about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she hopes the growing use of eDNA techniques and DNA analysis will help her team understand of the invasive species, funding for the research has been hard to come by.

"Everyone wants to give funding for preserving frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to manage."