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During her daily walk to the research facility, biologist the researcher crouches near a shallow pond covered by dense plants and retrieves a small green audio recorder.

She had placed there through the night to record the distinctive croaks of the Scinax quinquefasciatus, known by local researchers as an invasive species with consequences that experts are just beginning to understand.

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

During the 1990s, this shifted. Some small amphibians traveled from continental the mainland to the archipelago, probably as stowaways on transport vessels.

DNA studies suggest that, through time, there have been repeated accidental arrivals to the islands, and the frogs now have a firm foothold on two locations: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been struggling to monitor, estimating numbers in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When the biologist marked frogs and attempted to find them in the subsequent 10 days, she could locate just one tagged frog occasionally, suggesting their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I'm quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' abundance is clear from the acoustic chaos they create. "The amount of frogs and the noise – it's really insane," comments the scientist.

For the scientists, their nocturnal mating calls are useful in determining their presence in remote areas, using audio devices like the one outside San José's workplace.

But nearby farmers say the sounds are so raucous they prevent sleep at night.

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

"Initially it was a surprise, seeing the initial frogs in the area," says the farmer, who started noticing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, though. While the species has been in the islands for almost three decades, experts still know limited information about its impact on the archipelago's precariously balanced land and water environments.

On islands, it is very typical for non-native species to prosper, as they have few of their enemies. The Galápagos has 1,645 introduced types, many of which are seriously affecting the safety of its endemic ones.

A 2020 study indicates the invasive amphibians are hungry bug consumers, and might be disproportionately consuming rare insects found only on the islands, or reducing the food sources of the region's uncommon avian species, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their development process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for half a year.

"We really don't know this aspect," she says, concerned the tadpoles could be affecting the islands' freshwater, a very scarce resource in Galápagos.

Techniques to control the frogs in the beginning of the century were mostly ineffective. Conservation officers tried collecting large numbers by hand and slowly increasing the salinity of lagoons in vain.

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

Without answers to more of the fundamental issues about their biology and impact, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Research

While she expects the growing use of eDNA methods and genetic examination will assist her group understand of the invader, financial support for the research has been hard to obtain.

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