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During her daily commute to the scientific station, biologist the researcher stoops near a small water body surrounded by thick plants and collects a small green audio recorder.

She had placed there overnight to capture the characteristic croaks of the Fowler's snouted treefrog, known by Galápagos scientists as an invasive threat with consequences that scientists are starting to comprehend.

Although teeming with remarkable wildlife – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Darwin's theory of evolution – the island chain off the shoreline of South America had historically been free of amphibians.

In the late 1990s, this changed. Several tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as stowaways on transport vessels.

DNA research indicate that, through time, there have been repeated unintentional arrivals to the archipelago, 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 finding it difficult to monitor, estimating numbers in the millions on every island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to recapture them in the subsequent 10 days, she could locate just one tagged frog occasionally, indicating their populations were massive.

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

Deafening Noise and Rising Worries

The frogs' abundance is evident from the acoustic disruption they create. "The number of frogs and the noise – it's really incredible," says San José.

For the scientists, their nocturnal mating calls are useful in determining their existence in remote areas, using audio devices like the one near the office.

But nearby agricultural workers say the sounds are so loud they prevent sleep at night.

"During the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"At first it was a surprise, observing the initial frogs in the area," says the farmer, who started observing their abundance about several years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, however. While the amphibians has been in the islands for almost three decades, scientists still know very little about its effect on the islands' delicately balanced land and water ecosystems.

On archipelagos, it is very typical for non-native species to thrive, as they have few of their natural predators. The islands has 1,645 invasive species, many of which are seriously disrupting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are hungry bug consumers, and might be unevenly consuming rare bugs found only on the islands, or reducing the food sources of the region's uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

The island frogs have exhibited some atypical characteristics, including living in slightly salty water, which is uncommon for amphibians.

Their metamorphosis process is also extremely variable, with some larvae becoming frogs very quickly and others taking a long time: the researcher observed one which stayed as a larva in her laboratory for half a year.

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

Techniques to control the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually increasing the salt content of ponds in without success.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrocution could assist, but these approaches aren't always safe for other uncommon Galápagos organisms.

Without answers to more of the fundamental issues about their biology and impact, culling the frogs might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the growing use of eDNA techniques and genetic examination will assist her team understand of the invasive species, funding for the project has been hard to come by.

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