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During her daily walk to the research facility, biologist Miriam San José crouches near a small water body surrounded by dense plants and retrieves a compact plastic audio device.

She had placed there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, known by local scientists as an non-native species with consequences that scientists are just beginning to comprehend.

Although abounding with unique wildlife – including centuries-old giant tortoises, marine lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some tiny amphibians made their way from mainland the mainland to the archipelago, likely as stowaways on transport vessels.

DNA research suggest that, through time, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong foothold on two locations: Isabela and Santa Cruz.

The population is expanding so quickly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the subsequent week and a half, she could locate just one marked frog from time to time, suggesting their numbers were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic chaos they create. "The number of frogs and the noise – it's truly incredible," comments San José.

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

But local farmers say the calls are so raucous they prevent sleep at night.

"During the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a shock, seeing the initial frogs in the area," says the farmer, who started observing their large numbers about three years ago when one jumped on her hand as she was stepping out of her front door.

Environmental Consequences Remains Unknown

The sound isn't the primary problem, however. While the amphibians has been in the islands for almost three decades, scientists still know limited information about its impact on the islands' delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very common for non-native organisms to prosper, as they have few of their natural predators. The islands counts 1,645 invasive types, many of which are seriously affecting the survival of its endemic ones.

A 2020 study suggests the non-native amphibians are voracious bug eaters, and might be disproportionately consuming rare insects found exclusively on the archipelago, or depleting the nutrition of the region's uncommon birds, affecting the food chain.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual characteristics, including surviving in brackish water, which is rare for frogs.

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

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

Methods to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually raising the salinity of lagoons in vain.

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

Without solutions to more of the basic issues about their lifestyle and effect, removing the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and genetic analysis will assist her group make sense of the invader, funding for the project has been hard to come by.

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