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During her daily walk to the scientific station, biologist the researcher crouches near a shallow water body surrounded by thick vegetation and retrieves a small green audio device.

The device was left there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos researchers as an invasive species with effects that experts are just beginning to understand.

Despite teeming with unique animals – including centuries-old giant tortoises, swimming lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs traveled from mainland the mainland to the islands, likely 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 locations: multiple locations.

The numbers is growing so rapidly that scientists have been finding it difficult to keep track, calculating numbers in the millions on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When San José tagged frogs and attempted to recapture them in the following 10 days, she could find just one marked frog occasionally, suggesting their numbers were massive.

They estimated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

The frogs' abundance is evident from the sound disruption they cause. "The number of frogs and the noise – it's truly incredible," says the scientist.

For the researchers, their nightly mating calls are useful in estimating their presence in far-flung areas, using audio devices like the one near the workplace.

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

"In the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, observing the first frogs in the region," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Environmental Consequences Stays Unclear

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

On islands, it is very typical for non-native organisms to prosper, as they have few of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are significantly disrupting the survival of its endemic ones.

A 2020 study suggests the invasive frogs are voracious bug eaters, and might be unevenly eating rare insects found only on the islands, or depleting the food sources of the region's rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have exhibited some unusual traits, including living in brackish water, which is uncommon for frogs.

Their development process is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a long time: San José witnessed one which stayed as a tadpole in her lab for half a year.

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

Methods to control the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and slowly raising the salinity of ponds in vain.

Studies indicates spraying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't necessarily safe for other uncommon Galápagos species.

Lacking answers to more of the basic questions about their biology and effect, removing the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she hopes the increasing use of eDNA techniques and genetic examination will assist her group make sense of the invasive species, funding for the project 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."