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During her regular commute to the scientific station, biologist Miriam San José crouches near a small water body covered by thick plants and retrieves a compact green sound recorder.

The device was left there overnight to record the distinctive croaks of the Fowler's snouted treefrog, recognized by local scientists as an invasive threat with effects that experts are starting to understand.

Despite abounding with remarkable wildlife – including ancient large turtles, marine lizards, and the famous finches that sparked Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had long remained devoid of amphibians.

During the 1990s, this shifted. Some tiny tree frogs traveled from mainland Ecuador to the islands, probably as stowaways on cargo ships.

DNA studies indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm foothold on two islands: multiple locations.

The numbers is growing so rapidly that researchers have been finding it difficult to keep track, calculating populations in the millions on each 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 subsequent 10 days, she could find only a single tagged frog from time to time, suggesting their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," says San José. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic disruption they cause. "The number of frogs and the noise – it's really incredible," comments the scientist.

For the scientists, their nightly mating calls are useful in estimating their presence in far-flung areas, using recorders like the one outside the workplace.

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

"During the wet season, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

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

Ecological Impact Stays Unknown

The noise isn't the primary problem, though. While the species has been in the Galápagos for almost three decades, experts still know limited information about its impact on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for invasive species to prosper, as they have few of their enemies. The Galápagos counts 1,645 invasive types, many of which are seriously disrupting the safety of its native ones.

A recent research indicates the invasive frogs are hungry insect consumers, and might be unevenly consuming rare insects found exclusively on the islands, or depleting the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos frogs have shown some unusual characteristics, including living in slightly salty water, which is uncommon for amphibians.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her lab for six months.

"We really don't know this aspect," she says, concerned the larvae could be affecting the region's freshwater, a very scarce resource in the islands.

Methods to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried capturing significant quantities by hand and slowly increasing the salt content of lagoons in vain.

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

Without solutions to more of the fundamental issues about their biology and impact, removing the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she hopes the growing use of eDNA techniques and DNA examination will assist her team make sense of the invasive species, financial support for the project has been difficult to obtain.

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