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During her daily commute to the scientific station, biologist the researcher crouches near a shallow pond surrounded by dense vegetation and collects a small green audio device.

She had placed there through the night to record the distinctive croaks of the Fowler's snouted treefrog, recognized by local scientists as an invasive species with consequences that experts are starting to comprehend.

Although teeming with remarkable animals – including centuries-old giant tortoises, swimming iguanas, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this changed. Several small amphibians traveled from mainland Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic research suggest that, over the years, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a strong presence on two islands: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to keep track, estimating populations in the millions on each island, across developed and agricultural areas, but also in the protected natural reserve.

When San José tagged frogs and attempted to find them in the following 10 days, she could locate only a single marked frog from time to time, indicating their numbers were massive.

They calculated 6,000 frogs in a single pond. "Our estimates are still very low," says the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the sound – it's truly insane," says the scientist.

For the researchers, their nocturnal vocalizations are helpful in estimating their presence in remote areas, using recorders like the one outside San José's office.

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

"During the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

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

Environmental Consequences Remains Unclear

The noise isn't the primary problem, however. While the species has been in the islands for nearly 30 years, scientists still know very little about its effect on the archipelago's precariously balanced land and water ecosystems.

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

A 2020 research indicates the invasive amphibians are hungry insect consumers, and might be unevenly eating rare insects found exclusively on the archipelago, or reducing the food sources of the region's rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their development stage is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: the researcher observed one which remained as a larva in her lab for half a year.

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

Methods to control the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried collecting large numbers by manual methods and gradually increasing the salinity of lagoons in vain.

Research indicates spraying caffeine – which is extremely toxic to frogs – or using electrocution could help, but these methods aren't necessarily safe for other rare Galápagos species.

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

Financial Obstacles for Research

While she hopes the increasing use of eDNA methods and genetic analysis will assist her group make sense of the invasive species, funding for the project has been difficult to obtain.

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