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On her regular commute to the research facility, scientist the researcher crouches near a small water body covered by dense vegetation and retrieves a compact green sound recorder.

She had placed there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by Galápagos researchers as an invasive species with effects that scientists are just beginning to understand.

Despite abounding with remarkable wildlife – including ancient large turtles, marine iguanas, and the famous birds that inspired Charles Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some small tree frogs made their way from continental the mainland to the archipelago, probably as hitchhikers on transport vessels.

DNA research indicate that, through time, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a firm presence on two islands: multiple locations.

The numbers is growing so quickly that researchers have been struggling to keep track, estimating populations in the millions on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could find only a single marked frog occasionally, suggesting their populations were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am quite certain there are even more."

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the sound disruption they create. "The number of frogs and the sound – it's really incredible," says the scientist.

For the scientists, their nocturnal mating calls are useful in estimating their presence in remote areas, using audio devices like the one near the office.

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

"In the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

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

Ecological Impact Stays Unclear

The noise isn't the primary problem, though. While the species has been in the Galápagos for almost 30 years, experts still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic environments.

On islands, it is very common for non-native species to thrive, as they have few of their enemies. The islands counts 1,645 introduced species, many of which are significantly disrupting the safety of its native ones.

A 2020 study indicates the invasive frogs are voracious insect eaters, and might be unevenly eating rare insects found only on the islands, or reducing the nutrition of the islands' rare birds, affecting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a larva in her laboratory for six months.

"We really don't know this aspect," she says, concerned the tadpoles could be impacting the region's freshwater, a very scarce commodity in Galápagos.

Methods to control the frogs in the early 2000s were mostly ineffective. Park rangers tried capturing large numbers by hand and gradually increasing the salinity of lagoons in vain.

Research suggests spraying caffeine – which is extremely poisonous to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other uncommon island organisms.

Without answers to more of the fundamental issues about their biology and effect, removing the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of environmental DNA methods and genetic examination will help her team make sense of the invader, financial support for the research has been difficult to come by.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."