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During her regular commute to the scientific station, biologist the researcher stoops near a shallow pond surrounded by thick plants and retrieves a small green audio recorder.

The device was left there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by local scientists as an non-native species with effects that scientists are starting to understand.

Although abounding with unique animals – such as centuries-old large turtles, swimming lizards, and the well-known birds that sparked Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had historically been free of amphibians.

In the late 1990s, this shifted. Some small amphibians traveled from mainland the mainland to the archipelago, probably as hitchhikers on transport vessels.

Genetic research suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong presence on several islands: multiple locations.

The population is expanding so rapidly that researchers have been finding it difficult to monitor, calculating populations in the millions on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to find them in the subsequent 10 days, she could locate just one marked frog from time to time, indicating their numbers were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," states the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," says San José.

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

But nearby farmers say the sounds are so raucous they keep them up at night.

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

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

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the islands for almost three decades, experts still know very little about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive species to thrive, as they have few of their natural predators. The islands counts over sixteen hundred invasive types, many of which are seriously affecting the safety of its endemic ones.

A 2020 study suggests the invasive amphibians are hungry insect consumers, and might be unevenly consuming rare insects found exclusively on the archipelago, or reducing the food sources of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also highly inconsistent, with some tadpoles turning into frogs very quickly and others taking a long time: San José witnessed one which remained as a tadpole in her laboratory for half a year.

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

Methods to control the frogs in the early 2000s were mostly ineffective. Conservation officers tried capturing significant quantities by hand and slowly raising the salinity of ponds in vain.

Studies indicates spraying caffeine – which is highly poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other uncommon island organisms.

Lacking answers to more of the fundamental issues about their lifestyle and impact, removing the amphibians might not even be the right way to advance, says San José.

Financial Obstacles for Research

While she expects the increasing use of eDNA methods and DNA examination will assist her group understand of the invasive species, financial support for the project has been hard to come by.

"Everybody 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."